For example, hunter-gatherers are far more physically active than modern humans, and this prompts us to ask whether this accounts for their superior metabolic and cardiovascular health (Pontzer et al., 2018). And indeed, when we look at the evidence, we see a significant body of research finding correlations between physical activity level and health, and a large number of physiological mechanisms suggesting the relationship is causal.

Another interesting difference is the distribution of movement throughout the day. Children and hunter-gatherers tend to move all day long at relatively low to moderate intensity. Modern humans who achieve similar levels of total physical activity tend to move at higher intensity for a shorter time. For example, one hard hour at the gym, then ten hours of sedentary time in a chair. This is quite different from the natural pattern, where physical activity is more distributed, with less extended periods of inactivity (Raichlen et al., 2020).

Does this make a difference? Is extended sitting harmful in some way that can't be compensated by exercising later? Conversely, what is the potential value of getting up to stand and walk intermittently, or incorporating short movement snacks (two to five minutes of exercise) throughout your day?

In this post I’ll look at several lines of evidence that bear on these questions, including the the physiology of extended sitting as it relates to metabolic health, observational studies comparing time spent sitting to health outcomes, and RCTs examining the effects of “exercise snacks.”

The quick summary: for people who are already hitting the gym, breaking up extended sitting with short movement snacks probably has real but small benefits on top of what you’re already doing. For inactive people, the costs of extended sitting (and the benefits of movement snacks to break it up) are much higher. Read on for details and practical tips.

Metabolic health and the physiology of extended sitting

Metabolic health is basically how well your body stores and uses fuel, which includes managing blood sugar and lipid levels, making good choices about whether to burn fat or carbs, and stabilizing energy. It depends on communication between muscles, liver, pancreas, and fat tissue about what fuel is being used, what’s available, and what the blood sugar level is. When that communication works well, blood sugar is balanced, fat is burned when it should be, and hunger is regulated. This is sometimes called metabolic flexibility. The opposite condition is insulin resistance, and eventually metabolic syndrome — the cluster of problems that includes high blood sugar, high blood pressure, and obesity.

It’s well established that 30 to 60 minutes of moderate or vigorous exercise per day is very beneficial for keeping this system well-regulated (Bull et al., 2020). But some scientists wonder whether activity level during the rest of the day matters as well. Part of the concern is that sitting for a few hours creates a physiological state that resembles metabolic syndrome. It measurably increases post-meal blood glucose and insulin response, and reduces blood vessel function (Saunders et al., 2018). It’s normal for the body to drift into this state and then recover when physical activity resumes. The worry is that excessive time in a sedentary state, repeated day after day over years, gradually dysregulates the metabolic system, biasing it toward unhealthy patterns.

It’s also notable that the metabolic system is sensitive to even small changes in physical activity. Simply shifting from sitting to standing measurably changes heart rate, blood flow, muscle enzyme activity, and how quickly sugar is cleared from the blood. Even very small movements matter: in one randomized trial, people who intermittently fidgeted their legs during three hours of sitting had meaningfully lower blood sugar and insulin responses to a glucose drink than people who sat completely still (Pettit-Mee et al., 2021).

Given how sensitive the system is to small inputs, it’s reasonable to ask whether there are negative effects associated with prolonged states of inactivity.

Observational trials on extended sitting

One way to test whether long sedentary time is bad for you is to follow large groups of people, measure how much they sit, and see what happens to them. About a decade ago, this kind of research started producing alarming headlines like “Sitting is the new smoking.” According to the studies, prolonged sitting raised the risk of metabolic health problems, and this risk was independent of how much you exercised. This lead to the purchase of many standing desks.

More recent research presents a more nuanced picture. A large study pooled accelerometer data from more than 44,000 adults. (Ekelund et al., 2020), and found that the link between sitting and mortality depended heavily on physical activity during the rest of the day. Sitting a lot was clearly associated with higher mortality in less active people, but the association faded in those who engaged in 30 to 40 minutes a day of moderate-to-vigorous activity. (See also Sagelv et al., 2023; and Rezende et al., 2024).

Other data suggests that small changes in physical activity can affect health. A 2026 meta-analysis using device-measured data (Ekelund et al., 2026) estimates that a 5-minute-per-day increase in moderate or vigorous activity could prevent at least 6% of deaths. Reductions in sedentary time were also associated with substantial but somewhat smaller mortality benefits, independent of moderate or vigorous activity levels. In both cases, the least active and most sedentary people received the greatest benefit.

A related line of observational evidence comes from work on “vigorous intermittent lifestyle physical activity,” or VILPA — the brief vigorous bursts that happen during daily life, like hurrying across an intersection or carrying heavy groceries up a flight of stairs. A UK Biobank study of tens of thousands of self-described non-exercisers found that just three short bouts a day of one to two minutes each was associated with roughly 40 percent lower all-cause mortality and nearly 50 percent lower cardiovascular mortality compared with none (Stamatakis et al., 2022).

Of course, these observational studies can only show associations, not causation. It may be that people sit longer and have fewer bursts of energy because they’re less healthy to begin with. I suspect the causal arrow runs in both directions. Either way, I think it’s a good idea to notice how much you’re moving when you’re not at the gym, and to take opportunities to get moving when you have them.

RCTs on exercise snacks

Another interesting line of research involves the potential benefits of exercise snacks — short bouts of activity lasting five minutes or less, performed multiple times per day. Examples include brisk walking, climbing stairs, or doing bodyweight squats.

A 2026 meta-analysis of eleven RCTs (Rodríguez et al., 2026) found moderate-certainty evidence that exercise snacks produce large improvements in cardiorespiratory fitness in people who are relatively inactive. The gains were comparable to the effect sizes seen for traditional high-intensity interval training, despite a significantly smaller volume of total exercise per week. It should be noted that the meta-analysis found no beneficial changes in other measures of metabolic health (body composition, blood pressure, or blood lipid profiles). But this might be explained by the relatively short intervention period (6 to 12 weeks) and the fact that participants had fairly good metabolic profiles at baseline.

Another point worth noting is that adherence and compliance with exercise snack protocols were higher than typically seen in trials of more traditional continuous or high-intensity interval training. The likely explanation is that short bouts of exercise at home are more convenient than long trips to the gym.

The research on exercise snacks generally involves sedentary people, so it doesn’t directly address the potential benefits of exercise snacks for people who are already hitting the gym. Nor does it prove that the distribution of movement throughout the day matters in itself. Perhaps the benefit of exercise snacks is simply that they increase the total volume of physical activity per day, regardless of how that volume is distributed. In any event, the research suggests that multiple short bouts of exercise can have significant health benefits, especially for people who aren’t otherwise moving very much.

Takeaways

Based on the research, I think short movement breaks throughout the day are an underrated tool for better health that most people neglect.

Perhaps this is because people tend to think of “exercise” as something that requires an extended block of hard work, sweat, special clothes and equipment, and probably a trip to the gym. The above research suggests that’s wrong. You can get substantial fitness and metabolic benefits from short, simple movements done at home — a quick burst of stair climbing, a few sets of squats, or even just getting up to stand and walk around.

The benefits are especially large for people who are otherwise sedentary. There is a negligible difference between exercising for 60 and 65 minutes, but the difference between zero minutes and five is enormous. It’s like drinking a glass of water when you’re stranded in the desert — a small dose provides a huge benefit.

For more active people, a similar logic applies to specific types of movement: if there's a certain component of fitness that you’re not challenging, there is a huge benefit from getting just a little bit of it. A runner who never does any strength work might gain a lot from a few sets of push-ups and bodyweight split-squats spread through the day, at minimal cost. Someone who only lifts weights can obtain substantial benefits from adding some walking to their daily schedule. If mobility work is not done at the gym, its easy to check that box with a few stretching breaks done throughout the day. And it feels good.

This points to another benefit of movement snacks: they help you feel better throughout the day, often having the effect of adding rather than subtracting energy. My own experience is that 2-3 bouts of walks, stretches, hangs, or crawls leaves me feeling fresh, alert, and relaxed. Extended sitting creates the opposite feelings: stiff, sluggish, and sleepy.

I’ll close with another shameless plug for my ongoing online book: it includes exercises designed with exactly these considerations in mind — simple, equipment-free, and focused on movements that modern adults most commonly lose or neglect, and which therefore tend to provide large benefits in small doses: squatting, hanging, bodyweight strength work, crawling, overhead reaching, and rolling.

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References

Bull FC, Al-Ansari SS, Biddle S, et al. (2020). World Health Organization 2020 guidelines on physical activity and sedentary behaviour. British Journal of Sports Medicine. 54:1451–1462.

Ekelund U, Tarp J, Fagerland MW, et al. (2020). Joint associations of accelerometer-measured physical activity and sedentary time with all-cause mortality: a harmonised meta-analysis in more than 44,000 middle-aged and older individuals. British Journal of Sports Medicine. 54:1499–1506.

Ekelund U, Tarp J, Ding D, et al. (2026). Deaths potentially averted by small changes in physical activity and sedentary time: an individual participant data meta-analysis of prospective cohort studies. The Lancet. 407(10526):339–349.

Pettit-Mee RJ, Ready ST, Padilla J, Kanaley JA. (2021). Leg fidgeting during prolonged sitting improves postprandial glycemic control in people with obesity. Obesity. 29(7):1146–1154.

Pontzer H, Wood BM, Raichlen DA. (2018). Hunter-gatherers as models in public health. Obesity Reviews. 19 Suppl 1:24–35.

Raichlen DA, Pontzer H, Zderic TW, et al. (2020). Sitting, squatting, and the evolutionary biology of human inactivity. Proceedings of the National Academy of Sciences. 117(13):7115–7121.

Rezende LFM, Ahmadi M, Ferrari G, del Pozo Cruz B, Lee IM, Ekelund U, Stamatakis E. (2024). Device-measured sedentary time and intensity-specific physical activity in relation to all-cause and cardiovascular disease mortality: the UK Biobank cohort study. International Journal of Behavioral Nutrition and Physical Activity. 21:68.

Rodríguez MÁ, Quintana-Cepedal M, Cheval B, Thøgersen-Ntoumani C, Crespo I, Olmedillas H. (2026). Effect of exercise snacks on fitness and cardiometabolic health in physically inactive individuals: systematic review and meta-analysis. British Journal of Sports Medicine. 60(3):133–141.

Sagelv EH, Hopstock LA, Morseth B, et al. (2023). Device-measured physical activity, sedentary time, and risk of all-cause mortality: an individual participant data analysis of four prospective cohort studies. British Journal of Sports Medicine. 57(22):1457–1463.

Saunders TJ, Atkinson HF, Burr J, MacEwen B, Skeaff CM, Peddie MC. (2018). The acute metabolic and vascular impact of interrupting prolonged sitting: a systematic review and meta-analysis. Sports Medicine. 48:2347–2366.

Stamatakis E, Ahmadi MN, Gill JMR, et al. (2022). Association of wearable device-measured vigorous intermittent lifestyle physical activity with mortality. Nature Medicine. 28(12):2521–2529.

How strong is strong enough? The answer depends on your goal. A football lineman, a runner, and an elderly person hoping to stay independent all need strength in different amounts and forms. But if your goal is to be a generally capable and healthy human animal, a short answer might be this: strong enough to climb a tall tree.

Climbing demands that the arms and legs control and move the body against the force of gravity at a wide variety of angles and leverages. There are many climbing movements, but the key building blocks are fundamental pushing and pulling movements: pulldowns, rows, and dips for the arms; squats and step-ups for the legs. These are the same movements that form the basis of most gym training, and that’s no coincidence. Gym exercises work because they approximate the demands that shaped human anatomy over 50 million years in the trees. If climbing were an exercise class, it might be called variable single-limb bodyweight resistance training. Such a class would provide baseline functional strength, balance, mobility, and overall body coordination.

In this chapter, we’ll explore the evolutionary and developmental history of climbing, examine how it appears in hunter-gatherer populations and children, and consider the physical and coordinative demands it places on the body. We’ll also compare climbing with lifting and carrying — the other primal movements most associated with strength — and make a case that climbing-style movements deserve priority. Finally, we’ll look at some simple ways to modify common bodyweight exercises to capture more of the variability and challenge that climbing naturally provides.

Evolution of climbing

Locomotion in the trees is far more complex than locomotion on the ground. In Ground World, a quadruped can go wherever it wants by repeating the same basic crawling gait cycle. Each step looks rather like the one before, with only minor variations needed to change direction and speed. Locomotion is cyclical, repetitive, and rhythmic.

Tree World is different, because the substrate is highly irregular, three-dimensional, and in most places isn’t even there. Every other step is a gap you can fall into. The branches that support body weight can be thick or thin, stiff or flexible, angled horizontally or vertically. To navigate this environment, primates evolved a wide variety of climbing techniques, along with the coordination to execute them and the perception to determine which ones are necessary when. These demands probably account for much of the explosion in primate intelligence.

The following sections review some of the major climbing techniques identified by primatologists, arranged roughly in the order they emerged. We’ll note which ones our ancestors relied on, and which remain relatively natural for human bodies today.

Pronograde quadrupedalism

This means crawling on all fours on top of a branch, with the spine horizontal. This was the main climbing technique of the earliest primates, who were roughly the size of squirrels, and therefore relatively small compared to branches. This allowed them to walk safely on top of branches using movement patterns that were not much different from the way they crawled over flat ground.

But these techniques became less useful with increasing body size. Larger primates are too heavy to walk confidently on top of most branches, and they began relying on a different approach: reaching overhead and hanging on branches to support their weight.

Suspensory Climbing

Suspension promotes a more extended, vertical posture compared to the more compact horizontal position used in crawling-style climbing. It also opens up new possibilities for sideways movement, including pendulum-like swinging and brachiation. Human ancestors certainly engaged in a lot of suspensory behavior and were capable of at least some brachiation, as discussed in the previous chapter.

Vertical climbing

Vertical climbing involves a wide variety of movements, but here we will distinguish two basic skills: (1) climbing with the aid of horizontal branches, and (2) ascending a vertical trunk without any horizontal branches for support. This is essentially the difference between climbing a ladder and climbing a pole. Humans are quite good at climbing ladders but struggle with poles. This reveals something interesting about how our anatomy changed since our ancestors descended from the trees. To understand these changes, we can consider why chimps climb poles better than humans.

Ascending a pole requires the climber to press inward against the trunk from opposing sides with the hands or feet or both. The climber is essentially pinching the tree and creating friction. Chimps can maintain this pinch with one hand and the opposite foot while using the other diagonal to reach upward and pull down. This results in a climbing pattern that looks somewhat like crawling.

Chimps can do this because of several anatomical features: long arms, short legs and flexible ankles keep their center of mass close to the trunk; prehensile feet grip the bark like hands (chimps basically have four hands); bowed legs allow the knees to spread wide and direct forces inward with the feet. Chimps are also strong, about 1.5 times as strong as humans.

Humans have traded most of these features for bipedal efficiency. Our legs are long, our arms are short, our ankles are stiff, our feet don’t grasp, and our hips and knees are configured to apply forces straight down into the ground, rather than inward against a vertical trunk. Our muscles have also evolved to be less powerful than chimps but better adapted for endurance activities like long-distance walking and running. As a result, climbing a bare vertical trunk is difficult for humans.

Human climbers who need to climb poles often replace some of these lost adaptations with tools, such as shoes that provide friction and straps that effectively lengthen our arms.

Clambering

Clambering means climbing at variable angles — horizontally, vertically, or diagonally — with movements that are irregular, relatively slow, and changing with each step. When humans climb trees or rocks, they are usually clambering, because each movement differs from the previous one.

This requires planning and perception to determine the right path and the right series of movements to navigate it. This cognitive demand may have been one of the pressures that drove the evolution of primate intelligence.

The transition (back) to the ground

After about fifty million years in the trees, our ancestors began transitioning to bipedal locomotion on the ground. The transition started about 7 million years ago, but proceeded slowly. After about 4 million years, the australopithecines were walking upright, but they still had long arms, curved fingers, and other features of a climbing anatomy. They probably continued to sleep in the trees. A full commitment to ground-based life probably didn’t occur until the emergence of Homo erectus, around two million years ago.

In adapting to bipedalism, our legs lengthened, our feet stiffened, and our arms shortened. These changes made us better walkers and runners but worse climbers. However, as we’ll see in the next section, modern hunter-gatherers still climb frequently, and children take to trees and climbing structures easily. Thus, although we think of ourselves as ground-based creatures, our bodies still “expect” regular visits to the trees, or at least activities that simulate the demands of doing so.

Climbing in hunter-gatherers

A recent cross-cultural analysis of over fifty hunter-gatherer societies found that nearly nine in ten engaged in tree climbing, and most of those did so with considerable skill. Climbing happens in a wide variety of environments, and is used to collect fruits, nuts, hunt arboreal animals, and to ambush prey from above. Perhaps most importantly, climbing is a way to collect honey, which is a significant food source for hunter-gatherers across the world.

Honey accounts for fifteen to twenty percent of the yearly calories of the Hadza in Tanzania. The Mbuti consume roughly eighty percent of their calories from honeycomb during the 3-month honey season in the Congo. The Efe, also of the Congo, devote a third of their foraging time to honey acquisition and regularly climb to heights exceeding 20 meters. Batek men in Malaysia climb trees over fifty meters tall on a daily basis in pursuit of honey and fruit. Among the Semai, also of Malaysia, traditional marriage nuptials involved three questions of the groom, one of which was: “are you a good climber?”

From this evidence, some researchers have concluded that the biological and adaptive significance of human climbing has been underestimated.

Children and climbing

Human infants acquire climbing skills quite early compared to other physical abilities. Before age two, babies can barely walk and cannot yet run or jump. But they can climb. YouTube has numerous videos of toddlers in diapers scaling vertical walls in bouldering gyms.

Kids of all ages climb whenever they see an opportunity, scrambling up furniture, playground structures, or trees. Many of their games involve the idea that the ground is hot lava. Among hunter-gatherers, children begin contributing to real climbing tasks by around age six.

Children climb well compared to modern adults. An athletic adult would have a clear advantage over an eight-year-old in contests of speed, strength, agility, or endurance. But in a test of climbing ability in trees, on playground structures, or a bouldering gym, the adult would not be nearly so confident. This suggests that modern adults are doing less climbing than is natural.

The biomechanics of climbing

What kind of fitness does tree climbing develop? A quick summary might be that it challenges the body in ways similar to variable unilateral bodyweight strength training.

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Semantic debates can be useful. Good science requires a system of terms which correspond well to the relevant facts, are self-consistent, and establish conventions about how experts communicate. For pain physiology, we need terms that identify important phenomena, distinguish between them, have some internal logic, and get everyone on the same page when they communicate and write about these topics. For this reason, efforts by the IASP to develop a uniform set of terms is useful.

Unfortunately, the debates about pain terminology that I see on social media are generally not useful. Most are just ways to declare opponents “wrong” based on legalistic analysis of language, rather than substantive discussions of pain physiology. The result is confusion and people talking past each other.

Some of these problems are evident in the recent debate about whether “pain” can occur in the absence of “nociception.” A recent paper by Weisman, Quintner, and Cohen addresses this question by arguing that the common aphorism “nociception is neither necessary nor sufficient for pain” is false, and should be replaced with: “nociception is necessary but not sufficient for pain.”

The paper contains some discussion of relevant facts, but its arguments are primarily semantic, and these are confused and self-contradictory. The authors argue that current IASP terminology implies, as a matter of logic, that nociception is necessary for pain. But they also argue that the definitions of both “pain” and “nociception” should be changed to state this. And they stated specifically in an earlier paper that under current definitions, nociception is not necessary for pain. Thus, the paper is not really an attack on the aphorism, but on IASP terminology.

This is like arguing that Pluto is a planet because it would be a planet if we changed the definition of "planet." Here’s a detailed analysis.

The definition of “pain”

Weisman et al. argue that pain requires nociception by definition. Specifically, that the definition of pain proposed by the IASP logically implies that all pain must involve nociception.1 This argument is wrong. Here’s the IASP definition of pain:

An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage.

There’s nothing in this definition that states that pain requires nociception. The only requirement is an unpleasant conscious experience that feels like tissue is being damaged.

Weisman et al. argue that nociception is logically implied in the definition because it references “tissue damage”, and tissue damage implies nociception.2 However, the definition also refers to “potential tissue damage”, and uses the word “resembling” and the phrase “associated with.” These words make clear that the phrase “tissue damage” is there to describe what pain feels like (e.g pain feels like tissue is damaged), not to state a requirement about what causes the feeling.

The authors seem to recognize the point, arguing in various places that the IASP definition of pain is flawed and would need to be “recast” to support their claim that pain requires nociception.3 As detailed in the section below, the same pattern appears in how they use the term “nociception.” They cite the IASP definition of this term, but have previously admitted that it does not support their argument, and would need to be changed to show that pain requires nociception.

The definition of “nociception”

Weisman et al. analyze a list of pain phenomena, including phantom limb pain and experimental brain stimulation, and conclude that all of them involve “nociception.” Therefore, they argue, it is impossible for there to be pain without nociception.

But how are they defining “nociception” here? Are they using the IASP definition, or some other definition they would prefer? Although the paper refers to the IASP definition, this can’t be the basis for the argument that pain requires nociception. How do we know this? Because Weisman, Quintner, and Cohen wrote a previous paper in 2023 stating that under the IASP definition, nociception is not necessary for pain. Here are some details and background.

The term “nociception” was coined by Sherrington more than 100 years ago, but it wasn't formally defined by the IASP until 2008. In the interim, the word was used to mean different things in different contexts.

Sometimes the word is used to convey a broad meaning, encompassing all neural events involved in processing noxious stimuli. For Sherrington, it even included top-down modulation of those signals. In other contexts, the meaning of nociception is narrower, intended to distinguish sensory signaling that arises from detection of noxious stimuli at nerve endings in the periphery, from sensory signaling that originates from “ectopic firing” in nerve trunks as a result of neuropathy. This is an important distinction: in the first case, sensory signals are “encoding” a noxious “stimulus”, but in neuropathy, sensory signals are firing by mistake and not accurately reflecting any stimulus.4

Neither usage is right or wrong in an absolute sense, only right or wrong within a particular context. So what context was the aphorism using when it said you can have pain without nociception? As Weisman et al. themselves point out, the aphorism was first stated by John Loeser in 1980. And Loeser himself has clarified that the word nociception in the aphorism means peripheral nociception.

In 2008, the IASP tried to standardize terminology by defining nociception as: “the neural process of encoding noxious stimuli.” My reading of this language, along with the IASP’s distinction between “neuropathic” and “nociceptive” pain, suggests that the narrow meaning was intended, i.e nociception means sensory signaling originating in the periphery. But I acknowledge this isn’t clear.

More importantly, Weisman and co-authors have themselves conceded that the narrow interpretation of this definition is correct. In a 2023 paper addressing IASP pain terminology, they explicitly stated that the IASP definition of nociception requires transduction in the peripheral nervous system, thus excluding sensory signaling caused by neuropathy. In fact, they specifically stated that under the current IASP definition, nociception is “neither necessary nor sufficient for pain.” In other words, they have already conceded that under IASP definitions, the aphorism is correct. Here are the relevant quotes:

This codification of nociception occurred in 2008, even though the term had been in use for a long time. However, this definitional focus is solely on the transduction and encoding of a noxious stimulus, that is, on the function of the nociceptor and the newly-defined nociceptive neuron.

…

NACD [nociception as currently defined by the IASP] posits that nociception relates only to the recognition of a noxious stimulus via nociceptors, defined in the singular as “a high-threshold sensory receptor of the peripheral somatosensory nervous system that is capable of transducing and encoding noxious stimuli.

…

the concept of NACD [nociception as currently defined] is too narrow. Indeed, this should come as no surprise, given that [nociception as current defined by the IASP] is neither necessary nor sufficient for pain.

I was surprised to find this. I wasn’t expecting that, in my research to find papers that take the opposite position of Weisman, Quintner and Cohen, I would find one written by …. Weisman, Quintner and Cohen. What exactly is going on here?

Let’s review the timeline:

In 2023, they explicitly state that under current IASP definitions, nociception is not necessary for pain. In 2025, they state that nociception is necessary for pain, citing the IASP definitions as authority.

How do we resolve this conflict? A careful read of both papers shows that the authors want to redefine both “pain” and “nociception.”5 They want “pain” changed so that it specifically requires nociception. And they want “nociception” broadened significantly. This can be seen from their references to “nociception-in-some-form” and a “nociceptive apparatus,” terms that they do not define.6 This is a good example of how debates about pain terminology can create more confusion than they resolve.

So is the aphorism correct?

I’m not sure there’s a right or wrong answer in the absolute sense. It depends on the context and how you define nociception. It’s also worth noting that aphorisms are not intended to be precise statements about specific facts. They are short, memorable ways to describe general principles. As such, they lack specific context and do not express precise meanings. Legalistic analysis of their accuracy is therefore unlikely to be informative.

That doesn’t mean we can’t improve the way we talk about pain. Perhaps a better aphorism would be something like: “tissue damage is neither necessary nor sufficient for pain.” Or scientists could stop using it altogether. What would be the effect of this change?

Contrary to suggestions I’ve seen on social media, the aphorism is not a foundational premise upon which other facts and theories are based. It’s an eight-word summary of decades of research on hundreds of separate topics. Changing or “refuting” the aphorism wouldn’t overturn the research illustrating the disconnect between pain and tissue damage, or the role of psychosocial factors in modulating pain. To do that, you need to engage in analysis of research, not argue over definitions.

To their credit, Weisman and colleagues do discuss a variety of factual topics in their paper. These shed light on pain physiology, including phantom limb pain, the thermal grill illusion, and the anecdote about the nail in the boot. These analyses are part of a larger argument that appears in their work, which is that central factors in pain (especially the role of the brain, thoughts, and emotions) have been overrated, and that more peripheral factors such as inflammation have been underrated.

These are legitimate arguments, and I would not be surprised if Weisman and colleagues are correct about some of them. Perhaps the thermal grill illusion will be shown to result from demand characteristics. Perhaps thoughts, emotions, and expectancies have less effect on pain than we think. Perhaps we’ll learn that fibromyalgia is far more peripheral than central, or that the immune system is more powerful than the nervous system in modulating pain. Or that treatments aimed at changing thoughts and emotions (e.g. CBT, CFT, PRP or PNE) are not as effective as advertised.

These are open empirical questions about the relationship between peripheral and central factors in pain. The answers will come from detailed examination of specific evidence in specific contexts, not from redefining terms (and developing long lists of questionable fallacies7) so that the distinction between central and peripheral is blurred, and the role of the brain can no longer be conceived.

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Footnotes

Human babies can hang from overhead supports within months after birth. This surprising ability hints at something fundamental about our species: grasping objects and pulling the body toward them is one of our most basic physical skills.

This is because our primate ancestors spent tens of millions of years hanging from branches while living in the trees. For them, suspension was a routine resting posture, especially for feeding.

Children show an innate attraction to hanging from overhead supports, as shown by their interest in climbing trees or playground simulations of trees like monkey bars. Hanging and swinging from them develops grip strength, upper body mobility, and functional pulling strength.

And yet modern adults rarely hang as an exercise. They may do pull-ups or rows, but these more complex movements can miss some of the specific benefits available from simply hanging out. It’s a bit like practicing squats without ever spending any time simply standing.

This chapter explores the evolutionary and developmental history of hanging, how it appears in natural settings versus modern life, and provides exercises to reintroduce this fundamental movement.

The evolution of hanging

Many of the evolutionary adaptations that allow hanging (such as grasping hands, mobile shoulders, and upright trunk posture) were discussed in the previous chapter on reaching. This chapter focuses on the specific anatomical changes that allowed hanging.

The first primates didn’t need to hang because they were very small (about the size of squirrels) and could obtain food by simply walking along small branches of trees. However, as some primate lineages evolved into the first apes, their bodies became too heavy to walk safely on the thin outer branches where most fruits were located. So they developed a new strategy to help support their body weight: hanging from overhead branches.

Suspension created a new relationship to gravity, and opened a whole new world of possible movements and postures. Body weight could now be supported by pulling from above instead of just pushing from below. Several anatomical specializations evolved to make this possible.

The hand

In primates that hang frequently, the finger bones are elongated and curved, and the joints naturally bend into the shape of a hook.

Although human hands eventually shortened and straightened to allow more skilled manipulation of objects, their original hook-like design remains evident. Even with the hand at rest, it looks ready to grab a branch.

This shape explains why the handles we design for maximum grip security—barbells, pull-up bars, suitcases, hammers—are shaped like tree branches.

Grip strength and endurance

Maintaining a hook-shaped hand against the pull of gravity requires sustained work from the muscles that flex the fingers, which are located in the forearm. Suspensory primates evolved well-developed forearm flexor muscles for this purpose.

The wrist also became more mobile to allow the body to shift position under a stable grip. Suspensory primates have far more wrist mobility than quadrupeds, especially into rotation, but also in flexion, extension, and both radial and ulnar deviation. As with the shoulder, this enhanced mobility means that control must be provided actively by muscles, further increasing demands on forearm strength.

The elbow

Hanging is most efficient when the elbow is straight, which allows body weight to be supported more passively. Most quadrupedal mammals can’t fully extend the elbow because there is a large bony projection at the back (the olecranon process). This gives the triceps leverage to extend the arm. Primates evolved a shortened olecranon process, sacrificing some strength into extension, but allowing a full straightening of the elbow to make hanging more efficient.

The lats

The lats tend to be stronger in tree-dwelling mammals like gibbons, chimpanzees, and orangutans. In ground-based mammals, the lats work mainly as a forelimb retractor, pulling the arm backward during walking or running. But in suspensory primates, it becomes a sling that connects the arms to the back and pelvis.

Humans retain large and powerful lats, even though we no longer brachiate for a living. As such, it plays a major role in movements that integrate the shoulder and pelvis, including walking, running, throwing, and climbing.

Swinging and brachiation

Hanging originated as a static posture for feeding, but it eventually opened the door to new forms of locomotion. When the body is suspended from above, the lower half is free to swing like a pendulum, which is an efficient way to move the body through space.

The simplest version is swinging with both hands, like a trapeze artist, to bring the feet into contact with a distant branch. Brachiation is more complex, and involves the tarzan-like movement of swinging with one hand while the other reaches for the next branch.

Human ancestors were likely capable of at least some brachiation, and modern humans retain at least some of this ability. Children commonly brachiate across monkey bars on playgrounds without any formal instruction.

Development of hanging

As noted in the intro, babies can hang from overhead supported at astonishingly young ages.

This ability depends on the palmar grasp reflex, which causes babies to close their fingers around objects that are stroked across the palm. This reflex is present in other primates, and probably evolved to help babies hold onto Mom’s fur as she climbs through the canopy.

The naturalness of hanging and swinging is easily seen by watching young children on playgrounds, who start doing these movements spontaneously, and develop skills without instruction. If there is a bar within reach, they will start hanging from it, often while bringing the knees up into a position that aligns and stabilizes the trunk.

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In the previous chapters, we explored primal movement patterns that involve close proximity to the ground, such as rolling, crawling, and squatting. Now we shift our focus from Ground World to Tree World, looking at the movement patterns that first emerged when our ancestors adapted to life in the trees: reaching, hanging, and climbing. This chapter focuses on the most primal of these movements, which is reaching.

The ability to extend the hand far from the center of the body to grasp distant branches was an essential survival skill for our primate ancestors. Adapting to this challenge reshaped their entire anatomy, especially the upper body. Overhead reaching was especially transformative, leading to the evolution of vertical spines. Where the hand went, the body followed.

For human infants, reaching to grasp objects is one of their first intentional movements and a key developmental milestone that coordinates the hand with the eye and upper spine. It precedes even rolling and crawling, indicating its status as one of our most fundamental movement patterns.

Because reaching is so central to human function, it’s one of the easiest ways to evoke full-body coordination. The hand acts like a conductor’s baton, organizing distant parts of the body into unified action. Depending on its direction, a reach draws the whole body into flexion, extension, side-bending, or rotation. This makes reaching one of the simplest ways to develop coordinated spinal mobility, particularly into the extended positions that characterize upright posture.

However, the modern world is engineered to place everything within easy reach. We reach forward and slightly down hundreds of times daily to access laptops, phones and coffee mugs, but rarely up, back, or to the sides. The body follows the hand, and in the modern world, the hand is always directly in front of us. It’s no surprise that our bodies are following—head and shoulders forward, chest collapsed. The easiest way to address this deficiency is to engage in varied reaching, especially upward.

In this chapter, we’ll explore how reaching emerged as our ancestors adapted to arboreal life, examine its role in infant development, and provide exercises that restore varied reaching patterns. It is one of the simplest ways to develop functional upper body and spinal mobility. Combined with the variable squat sitting discussed in the previous chapter, these movements provide nearly everything you need for full-body functional mobility.

The evolution of reaching

The great majority of animals that climb trees (e.g., squirrels, bears, raccoons) use claws to grip bark. This allows them to climb in a way that is not much different from how they walk over the ground. For them, climbing is much like vertical crawling.

Our ancestors, however, evolved a different locomotive strategy when they moved into the trees about 55 million years ago: grasping hands and feet with flattened nails instead of claws. This technique, called frictional gripping, is almost unique to primates among mammals. Grasping hands allowed an extraordinary diversity of postural and locomotor behaviors, such as reaching for distant branches and fruits, hanging while resting, and swinging hand-to-hand. These abilities were made possible by major transformations of the upper body, especially the shoulder.

Terrestrial quadrupeds have shoulders designed to absorb the compressive forces of walking. Their shoulder sockets point downward and forward, and the humeral head sits in a deep socket for stability. The head is shaped like a cylinder, which favors movement forward and back while limiting motion side to side.

Primates evolved a different design that allowed reaching in many directions, especially overhead. The humeral head became more round, and the socket shallower, increasing freedom of movement. The socket also rotated upward and outward, facilitating overhead and lateral reaching. With less bony stability, primate shoulders relied more on the rotator cuff muscles for support.

As apes evolved, the thorax became broader and flatter, allowing the scapula to migrate from the side of the ribcage toward the back, where it could move more freely in support of varied reaching movements. The scapula also gained greater range into elevation, upward rotation, and posterior tilt—all of which improved upward reach. Meanwhile, the thoracic and lumbar spine, along with the hip joints, gained additional range into extension and rotation, further enhancing the reach of the hand.

Importantly, these gains in mobility were not just about range of motion, but also variability in how that range could be achieved. Unlike hinge joints like the knee or elbow - which offer large ranges of motion but few degrees of freedom - the shoulder complex is capable of thousands of different combinations of movements at the shoulder joint, scapula, and spine. This means that a particular target can be hit with precision from different postures, using different trajectories, and different rotations of the hand.

This freedom of movement created a corresponding challenge for the nervous system. Primate eyes moved forward and closer together, improving depth perception for judging distances to branches and fruits. The visual areas of the brain expanded, enhancing hand–eye coordination. Primates also developed dedicated brain circuits for guiding the hand through space.

The result is that reaching to a target became one of the most coordinated and precise movements that humans make. When you reach for an object on a high shelf, the thoracic and lumbar spine, pelvis, knees, and ankles extend in a smooth sequence. When you reach across a table for a glass of wine, the hips flex to push the shoulder forward. Accuracy requires orchestration of nearly every joint in the body—wrist, elbow, shoulder, scapula, spine, ribs, and even hips and ankles. Of all the intentional movements humans perform, few so effortlessly recruit the entire body into coordinated action.

Development of reaching

Reaching appears far earlier on the developmental timescale than on the evolutionary timescale. Our ancestors spent millions of years perfecting quadrupedal locomotion before they climbed trees and began reaching overhead. But infants start extending the hand away from the body to reach objects at about 3-4 months, well before they can roll efficiently or crawl. This reveals how fundamental reaching is to human function. The nervous system prioritizes the ability to extend the hand toward targets above nearly every other movement skill. And it uses a wide variety of patterns to accomplish this task.

When babies reach forward while lying on their stomach, the spine and hips extend; reaching while sitting requires flexion; reaching to the sides or at diagonals incorporates rotation and side-bending. Each variation teaches the nervous system how different body segments—shoulder, scapula, ribs, spine, and pelvis—must organize around the simple intention of placing the hand on a target.

Reaching also drives other developmental milestones. Infants often roll for the first time in response to the impulse to reach a toy that sits just beyond their grasp. The first attempts at crawling emerge when reaching while prone. Even the transition to standing begins with upward reaching—pulling to stand on a couch or crib rail (as discussed in the previous chapter on squatting).

The challenge of reaching

To understand the benefits of reaching as an exercise, we need to examine what it demands from the body. Reaching primarily challenges mobility and coordination. Here are some relevant details.

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Most approaches to teaching movement are “corrective” in nature - the client is told they’re moving the “wrong” way, shown the “right” way, and asked to repeat what they’re shown. This strategy has at least two weaknesses. First, there’s rarely just one correct way to move, and therefore what works for one person might not work for someone else. Second, people learn to move best through trial and error, not being told what to do. The Feldenkrais Method® has concepts and practices that can help avoid both problems, and make motor learning more exploratory and individualized.

In this webinar I will talk about some key principles from Feldenkrais, and do some short movement explorations based on Feldenkrais lessons. We’ll take familiar exercises like cat-cows, bird dogs, squats, or bridges, and demonstrate how incorporating Feldenkrais-style strategies can make them more exploratory, individualized, variable, and effective.

Details for Beyond Corrective Exercise: A Feldenkrais Approach to Motor Learning

• Price: 75 CAD ($53).

• Date and Time: October 29, 19:00 (EDT).

• Duration: Two hours

• Recording: Available for download if you can’t attend live.

• CEU Credits: Available in approved states.

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For more information on Feldenkrais, click here for an FAQ.

We tend to think of squatting as being about going down, but from an evolutionary and developmental perspective, it's more about going up. For both babies and our terrestrial ancestors, the story of movement begins with the spine flat on the ground, and nothing interesting happens until the limbs push the body up. For humans, the most powerful way to accomplish this fundamental task is the squat.

​​Squats push the body upward with “triple extension” - the coordinated straightening of the ankle, knee, and hip. Triple extension provides the power for almost every explosive movement that humans make, including vertical jumps, sprints, or throws. And it occurs in subtler form with every step we take. The simplest and most primitive expression of this pattern is simply rising from a deep squat to standing.

This is a long distance in functional terms—from a position that is low and flexed to one that is tall and straight. In terms of the “four worlds” concept discussed in preceding chapters, squats move us back and forth from Ground World and Bipedal World. It is the quickest, smoothest, and most powerful connection between sitting and standing, the two stable endpoints of the human postural landscape. If movements were roads, the squat would be the main highway with the biggest and most powerful vehicles.

Unfortunately, modern humans don't visit Ground World very often, and when they do, they are unlikely to spend much time resting in a deep squat position. Instead, they squat up and down from chairs and couches, cutting the squat highway in half, and depriving themselves of dozens of movements per day that could be helping to build mobility, strength and coordination in the lower body.

In this chapter, we'll consider the evolutionary and developmental history of squatting, discuss how squats appear in natural settings versus modern life and the gym, and provide exercises to practice squatting in ways that provide the highest return on health and performance with minimal investment of time and effort.

Evolution of squatting: the road from sitting to standing

To understand the evolution of squatting, let's examine how it manifests in three different stages of our evolutionary history – the quadrupedal stage (Ground World), the primate stage (Tree World) and the human stage (Bipedal World). The general trend is that over time (about 350 million years!) the distance between sitting and standing becomes longer, and the legs do more of the work of crossing it. 

Quadrupeds and triple extension 

The first land animals established the basic method for raising and lowering the body from the ground that is used by almost every other land animal – coordinated extension of three joints in the front and back limbs (the ankle, knee, and hip in the hindlimbs, and the wrist, elbow, and shoulder in the forelimbs.) When these joints flex, the limbs fold and the body lowers; when they extend, the limb lengthens and pushes against the ground.

When quadrupeds "squat," they simply drop their pelvis toward their heels through triple flexion while keeping their front limbs extended for support. 

Some quadrupeds can rise from a squat to stand tall on two legs (like a bear rearing up to fight). But they can't do this with much efficiency or stability because this isn't a neutral position for their spine or pelvis. This starts to change with the first primates, who gained functional range of motion into more extended postures.

Primates and squatting movements  

When our ancestors moved to the trees, reaching overhead and climbing upward became key skills. The hips evolved to produce force over a larger range of motion, including deeply flexed positions to step onto branches and pull the body upward, and fully extended positions that brought the spine in line with the legs and allowed the arms to reach higher. Further, the spine became "orthograde", meaning its neutral position was vertical, not horizontal. 

These adaptations changed how our ancestors could move between sitting and standing on two feet. Apes can sit in deep squats with their hands completely free and their spine comfortably vertical, then rise smoothly through triple extension all the way to standing tall. 

Human squatting 

Although non-human apes can walk on two legs, they do so with bent hips and knees. Humans became much more efficient at walking by straightening and lengthening their legs, increasing power into hip extension, and shortening the arms. 

The tradeoff was that squatting became more of a challenge. The distance between standing and sitting became greater, our arms became less able to help with the transition, and we became slightly weaker at rising from a deeply flexed position. But we retained the ability to sit in deep squats as a fundamental rest posture. We see this in hunter-gatherers, children, and many populations where sitting on the floor is a cultural norm.

Development of squatting 

Children sit in deep squats with ease, and move in and out of them all day as they interact with the ground. 

They start to develop this ability around 9-12 months. Their first efforts to stand involve reaching upward onto couches or cribs and then trying to extend the legs while the hands provide support and balance. These are called “pull to stand” movements. Like the first primates, the arms assist the transition from Ground World to Bipedal World by reaching upwards. 

The pull-to-stand movement is often performed from a half-kneeling position, with one leg in front and the other resting on the knee (resembling a "marriage proposal" pose). This develops triple extension coordination and strength in the front leg.

Descending from standing into a deep squat is a more difficult skill and involves many falls. The first clean transitions involve the hands moving to the ground first, while the pelvis remains higher in the air, so the hands can provide balance as the pelvis lowers to the heels.

After a few months of practice, infants learn to rise from and descend to deep squats without assistance from the hands. At this point, the deep squat becomes a frequent rest position that is used during play time with toys. As such, it is constantly being modified to allow reaching forward, back, and to the sides. There are fluid transitions to crawling, and other sitting positions like side-sitting, kneeling, or half-kneeling. In this sense, the deep squat serves as the hub of a movement network that connects sitting to standing and crawling. Thus, if squatting is the main highway between the world of the ground and standing, the deep squat is the intersection that connects the local side streets.

Squatting in hunter-gatherers

Squatting is easier for kids than for adults for several reasons: they have body proportions that provide better leverage (shorter legs, longer torsos and bigger heads) and they have higher levels of joint mobility (which allows deep flexion at the ankles and hips.) But adult humans who regularly spend time on the ground retain the ability to sit easily in deep squats even into old age. I can recall visiting Viet Nam and seeing 80-year old people on the sidewalk sitting and rising from deep squats with fluidity and ease.

A study of the movement behaviors of the Hadza tribe in Tanzania found that they spend substantial time resting in deep squats each day (close to 2 hours) and make an average of 37 sit to stand transitions per day, the majority of which would be performed through squatting-like movements. This video shows an example of their impressive mobility (filmed by Frank Forencich):

Notice the fluency of their movement in and out of the squat position. They can easily reach forward or to the side, and even take small steps in variable directions.

Let’s consider in more detail the physical challenge of this lifestyle and compare it to one where the “ground” has been raised to the level of a chair.

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I think disgust helps to explain some of the obsessive-compulsive, quasi-religious, polarized, and not very smart commentary on nutrition that we see on the internet.

Disgust defined

Disgust is an aversive reaction to potential toxins. It is experienced by almost all organisms, even very primitive ones, and evolved to provide protection against ingesting potentially harmful substances. As such, it is considered part of the “behavioral immune system” - a way to avoid pathogens instead of battling them inside the body.

The expression of disgust involves a strong sense of visceral revulsion and a characteristic facial expression.

Different human societies are disgusted by different things. But although disgust can be learned and modified by culture, some things seem to be universally disgusting, which are:

• bodily fluids (e.g. blood, spit, feces, urine, vomit)

• spoiled meats (dead animals)

• live organisms that are common carriers of disease (cockroaches, fleas, rats);

• visible signs of infection.

Did you notice what all these disgusting substances have in common? The essential quality of an inherently disgusting object seems to be that it is a potential carrier of microscopic pathogens.

Germs have some very particular characteristics that are relevant to understanding the nature of disgust. First is that they are too small to see. Second is that contact with even the tiniest amount of a pathogen can cause a deadly disease, because they can multiply exponentially.

Thus, in order to effectively promote safe behavior in the presence of potential pathogens, disgust should encourage an animal to completely and totally avoid contact with potential carriers, even without strong confirming evidence that they are actually contaminated. It’s not good enough to just limit your contact, or eat some of it. Even the smallest morsel of contaminated meat can be as bad as a whole steak. So you need to be an extremist when it comes to germs, and that is what a sense of disgust will encourage you to be.

Here’s a fun passage from the excellent book The Blank Slate by Steven Pinker, where he describes how disgust can be powerfully antirational:

People won’t eat soup if it is served in a brand-new bedpan or if it has been stirred with a new comb or flyswatter. You can’t pay most people to eat fudge baked in the shape of dog feces or to hold rubber vomit from a novelty store between their lips. One’s own saliva is not disgusting as long as it is in one’s own mouth, but most people won’t eat from a bowl of soup into which they have spat.

Are you starting to see how the experience of disgust might discourage moderate stances in a debate about nutritional toxins?

Nothing in moderation

A staple of solid nutritional advice is “everything in moderation.” While this is rather simplistic and does not rise to the level of universal truth, there is some logic here. Many nutrients that are good for you in moderation are actually deadly at large doses. And some toxins that are deadly at moderate doses are actually beneficial in very small doses.

For example, water is very beneficial if you are dehydrated, but adds very little additional value after that, and can actually kill you if you drink too much. On the other hand, excessive exposure to X-rays can cause cancer, but small amounts seem to prevent it, probably by upregulating anticancer processes (hormesis). Many experts believe that veggies are good for you precisely because their toxins cause a hormetic effect. So the dose makes the cure, and the dose makes the poison. It is therefore often a mistake to completely avoid a food you think may be toxic. But that is exactly what a sense of disgust will encourage you to do.

Many vegetarians or vegans will go to great lengths to avoid consuming even the tiniest quantities of meat. I recall a vegan friend almost puking after eating a meal she later discovered was made with beef bullion as a flavor base. Paleo dieters will sometimes get OCD worrying about whether a food is "primal." At the Whole Foods where I shop, the organic and nonorganic bulk spices have separate scooping spoons! As if one grain of inorganic turmeric will somehow spoil my curry. The residents of a town near Portland Oregon elected to have their entire eight million gallon reservoir of drinking water drained, at the cost of $50,000, after discovering video of a man peeing in the lake. (Even though other animals are basically pooping in the lake all the time.)

I could go on and on about this - there are as many irrational avoidances as there are people. Fat, carbs, sugar, HFCS, GMOs, squats with the knees past the toes, Crossfit, stretching, running, these are all alleged toxins that many people will try to limit completely, even though there is no rational reason to do so.

The evolution of disgust

Because disgust is such a primal and basic emotion that emerged so early in our evolution, the neural structures which create it became a building block for many other more sophisticated emotions and thought patterns that have an aversive nature.

For example, moral disgust is a revulsion to associating with individuals who violate group norms. Sexual disgust discourages mating with a biologically costly partner. In fact, artistically sensitive people experience the same basic reaction to bad art as a dog would to rotting meat.

Jonathan Haidt thinks that disgust is the foundation for religious ideas about purity, sacredness, sin, and defilement. Many religions such as Judaism, Islam, and Hinduism have extensive rules for keeping classically disgusting objects such as bodily fluids and meats separate from sacred objects and practices.

Research has discovered some interesting connections between the sense of disgust and seemingly unrelated emotions or behaviors. People with a stronger sense of disgust to food are more likely to have obsessive or anxiety disorders such as OCD, anorexia, and certain phobias like fear of spiders and needles. They are also more likely to be fear people outside their cultural group, and to have negative attitudes towards obese people. Deciding that a particular food is unhealthy often leads to moralizing about consumption of the food - others who consume it are deemed to be morally inferior.

I think this research sheds light on many irrational behaviors we see in regard to food (and other health related behaviors such as exercise) - the idea that it has spiritual significance, the polarization between different nutritional camps, and problems like anorexia and orthorexia. Is it any wonder that intelligent rational debate is difficult?

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In the previous chapter, we explored how rolling challenges a fundamental postural skill: controlling the spine as it tilts, bends, and rotates. Crawling builds on that foundation by adding a new layer of complexity - coordinating spinal alignment with precise movements of the four limbs to create locomotion.

Together with squatting (covered in the next chapter), rolling and crawling form the foundation for moving with agility while close to the earth. These “ground flow” movements build the basics of overall body coordination. They fit into exercise programs as corrective work, warm-ups or brief movement snacks during the day.

Crawling is especially valuable for overall coordination because it engages our most deeply rooted movement patterns. Our ancestors spent almost 400 million years perfecting quadrupedal locomotion before learning to walk upright just 4 million years ago. Almost everything about the structure and function of human bodies - the spine, shoulders, hips, and all the major muscle groups connecting them - was originally designed for movement on four limbs, not two. Thus, walking is essentially crawling with some minor updates to the software and hardware.

This means crawling serves as an excellent “reminder” to the nervous system about how to coordinate all the major joints and muscles of the body. This may be useful to modern humans who rarely challenge themselves to move skillfully with their hands on the ground and their spine horizontal. 

In this chapter, we’ll examine the evolutionary history of crawling, how it develops in human infants, and provide a series of videos demonstrating crawling exercises.

The development of crawling in infants

Human infants start trying to crawl around four months while lying on their stomachs. They wriggle and flail their limbs, but they can’t really go anywhere because their chest stays pressed to the ground.

The first breakthrough involves pushing the head and chest away from the floor with the hands and forearms. This may allow the forearms to pull the body forward in some “commando”-style crawling, with the belly on the floor and the knees splayed out to the side. 

By 7-10 months, most infants progress to supporting their chest with their hands and moving their knees underneath their hips, elevating the belly away from the floor. This posture allows the classic hands and knees crawling, where the right arm works with the left knee and vice versa.

As noted in the earlier History of Movement chapter, this developmental progression has striking parallels with the evolutionary progression of quadruped locomotion in our ancestors, starting with the first creatures who emerged from the ocean 375 million years ago. It starts with a push-up by the front limbs, proceeds to reptilian-style crawling with the limbs splayed out to the sides and the belly low to the ground, and becomes far more efficient with mammalian-style locomotion, with the hands and feet directly under the shoulders and hips, the belly away from the ground, and the limbs free to swing directly forward and back under the spine.

The takeaway is that there are relatively few solutions to the problem of moving a vertebrate body with four limbs over the ground, and most of them look similar across the animal kingdom. Nearly every vertebrate animal that cannot fly carries a deep heritage of quadrupedal locomotion encoded in their DNA, and humans are no exception.

The challenge of crawling

Crawling seems simple, but it requires coordination from all the major muscles and joints connecting the shoulder and hips. 

One key requirement is reciprocal limb movement, meaning the limbs move in alternation. For example, as the right hand lifts and swings forward, the left hand is pushing into the ground and extending backward. Another requirement is “cross-lateral” patterning between the arms and legs - when the right hand reaches forward, so does the left knee. This diagonal pairing ensures the body remains balanced as supporting limbs are continually removed from the ground. 

The more difficult challenge is controlling the spine, which needs to be mobile enough to allow reaching, yet stable enough to avoid collapse as the body transitions its points of support. The human spine contains 24 vertebrae, each allowing motion in multiple directions - flexion, extension, lateral bending, and rotation. This means the spine can be in a vast number of configurations at any given moment. But only a narrow subset of these will result in efficient, stable crawling. 

To move and stabilize the spine in useful patterns, every muscle between the hips and the shoulders needs to cooperate. The deep stabilizers of the spine (such as the multifidus and transverse abdominis) fire at precise times when stiffness is needed. Many of the larger muscles organize into chains that fire in diagonal patterns across the front and back of the body  - these include the glutes, lats and spinal erectors in the back, and the pectorals and obliques in the front. These diagonal chains create a dynamic bracing system that stabilizes the torso while transmitting force efficiently from the ground to the body.

The nervous system coordinates this muscle activity by using reflexive neural structures in the spinal cord. For example, the crossed extensor reflex links flexion of one leg to extension on the other. You can easily feel this: if you actively lift one knee toward your chest, the opposite leg will reflexively extend.

This reflex is part of a broader class of neural circuits called central pattern generators (CPGs). These produce rhythmic locomotive movements like crawling or walking without input from the brain. The advantage of reflexive control is that it operates far more quickly and efficiently than control which depends on participation from the higher centers of the nervous system.

Quadrupedal versus bipedal gait

The neural and muscular patterns used in crawling also appear in walking and running. Each relies on cross-lateral coordination between the arms and legs, controlled by central pattern generators (CPGs) in the spine. But there are important differences that help explain why humans benefit from occasional crawling, even though our primary mode of locomotion is bipedal. The main distinction is that walking demands less muscular work and coordination from the body's largest, strongest, and centrally located muscles.

In walking, trunk muscle activation drops to very low levels because the vertical spine position provides stability for free. The hip extensors work significantly less because the calf muscles take over almost half the work of forward propulsion. And the shoulder muscles are free to relax almost completely, while in crawling they are working hard to support the body.

Further, crawling requires the arms to move in coordination with the legs, but in walking the arms are free to move out of sync with the locomotive rhythm. This is because CPGs in humans have a slightly weaker connection to the legs than in quadrupeds, freeing the arms to operate independently when necessary for activities like carrying or throwing.

The cumulative result is that walking requires less work from the large muscles in the middle of the body and less coordination between them. This is why crawling remains a valuable practice—it "reminds" the nervous system how to activate and coordinate the body’s most powerful muscles in the most fundamental and useful patterns of movement.

Interestingly, the need to integrate the large powerful muscles into locomotor patterns reappears in sprinting. When we sprint, the shoulders must move in rhythm

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I’m providing it as a supplement to the rolling videos I provided in the previous chapter of my online book, Healthy Movements for Human Animals.

The videos in the previous chapter were self-explanatory, but also pretty short. So I wanted to show you how to explore these movements in far greater detail.

The lesson is recorded from an online class I taught last fall, done in the style of a Feldenkrais Awareness Through Movement lesson. It involves very simple movements, goes very slow, asks you to pay close attention to what you are doing, and experiments with variations. There is no video but you don’t need any. The instructions are very clear!

I recommend trying this as a way to discover how much smoother and easier you can move when you engage in some mindful exploration. Get the feel and then apply to whatever else you do.

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In the previous chapter, we examined how human movement can be understood in terms of four distinct functional environments that shaped our evolution: Ground World, Tree World, Bipedal World, and Tool World. Ground World is the foundation, and consists of movements we perform in close proximity to the earth, such as rolling, crawling and squatting. These movements build the mobility and postural control that supports the movements we do in standing.

Hunter-gatherers and children spend hours each day in Ground World, skillfully transitioning between a variety of different postures while working or playing. This develops what I call “ground flow”, which means moving with agility near the ground.

Most modern adults have lost their ground flow, and rolling is the best place to start in trying to recover it. It’s the most basic movement in Ground World, and literally the most grounded you can be while still moving. It’s also the easiest way to make smooth transitions between ground-based positions, connecting lying, sitting, and crawling. More importantly, rolling develops the fundamental postural skill of "righting" - controlling your body as it changes orientation to gravity. This skill forms the foundation for balance and coordination in more complex movements.

This chapter reviews the evolutionary and developmental history of rolling, how it appears in natural settings and in sports, and the way it’s used in athletic training and rehabilitation. Then it provides a series of videos demonstrating rolling exercises you can practice on your own, as a way to improve basic postural skills and body awareness.

The function of rolling

Rolling serves two basic functions: changing position while lying down (e.g. from back to front) or transitioning from lying to sitting. In the modern world, we associate these movements with leisure, and therefore consider them to be of little functional importance. But in the natural world, rolling plays a key role in at least three contexts that involve physical emergencies: getting up quickly to flee danger, absorbing the impact of a fall, and maneuvering during ground-based combat. Let's consider them in turn:

Fleeing. Imagine lying on your back and then noticing the approach of a dangerous predator. You need to roll quickly to a quadruped position, similar to a sprinter's starting position, before rising and running.

Falling. If you fall while running, you will land much easier if you roll through the fall. Rolling comes up frequently in sports when athletes expect to hit the ground with force, such as parkour, judo, or soccer goalkeeping. Sometimes the rolling pattern that allows a graceful fall is the mirror image of rising from the ground to run. Both scenarios have something in common - a quick transition between vertical and horizontal posture under chaotic conditions.

Ground combat. Consider the movements of dogs during play fighting - a fundamental move involves rolling from a defensive position on their back to an offensive stance on their front. Jiu-jitsu practitioners and wrestlers are constantly making the same transitions. In fact, they often call their practice “rolling.”

The above movements happen only rarely, but they directly impact survival, so natural selection placed strong pressure on our ancestors to adapt to them. The key skill common to each is controlling the body as it makes large and dynamic changes in its orientation to gravity. This is called "righting," which simply means moving from the “wrong” position to the right one. It is dramatically shown by a cat's amazing ability to "right" itself in the air during a fall through rolling.

Righting presents a unique postural challenge. In just seconds, you go from facing up, to facing sideways, to facing down. Gravity keeps changing its direction of pull, so you need to constantly change the patterns of muscular activity that are providing postural stability. Vestibular organs in your inner ear sense each change in head tilt, then communicate directly with the spinal cord to adjust muscle tone throughout your body. Front muscles (anterior chain) work when you are face up, side muscles (lateral chain) when you're on your side, and back muscles (posterior chain) when you're face-down.

These same righting processes control posture in upright standing, but in a more subtle way. Even as we stand still, our center of mass is always “falling” a bit to one side, moving back to the center, and then falling again, so that we are always oscillating just a few millimeters around a center point. When your head tilts in one direction (either forward, back, left, or right), chains of muscle on the opposite side automatically engage to bring the body back to center.

Rolling activates these same righting mechanisms, except with far greater amplitude and speed. This may be why rolling precedes upright postural balance in the developmental sequence.

Rolling and infant development

When infants begin rolling around 4-6 months, they're learning to control and refine these patterns of postural control. This involves two distinct stages. At 4-5 months, infants start “log rolling”, which means the entire body moves as one unit - the head, shoulders, trunk and pelvis all turn together. 

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In the previous chapter, we looked at the History of Human Movement, following the 400-million-year evolution of our ancestors from quadrupeds walking on all fours, to primates climbing trees, and finally to humans walking upright and manipulating objects. Each stage of evolution developed physical capacities that we can still access today. 

In this chapter, we’ll use that history as a lens to categorize the various ways we can move. We’ll identify four distinct environments or “worlds” in which each of our primal movement abilities evolved, and which humans living in natural settings continue to visit:

• Ground World: Movements performed close to the ground, which are built on the foundation of our quadrupedal heritage (sitting, squatting, crawling, rolling.)

• Tree World: Movements that involve using strength to move our bodyweight up and down in vertical space (reaching, hanging, climbing).

• Bipedal World: Locomotive movements on two feet at a variety of speeds and directions (walking, running, jumping and agility).

• Tool World: Movements that involve manipulating objects (lifting, carrying and throwing).

This environmental perspective is useful for several reasons. First, it provides an easy way to simplify the complex task of categorizing human movements, which are incredibly diverse and varied. Second, it helps us identify the essential components of a healthy movement “diet.” Third, it suggests ways to progress or regress exercise to meet individual needs. Fourth, it makes us more aware of opportunities for healthy movement in our daily environment. 

In this chapter, we'll explore how hunter-gatherers and children naturally move within each world, examining what physical challenges they encounter, and what fitness qualities they develop as a result. We'll also look at how modern exercise methods attempt to recreate similar challenges. The goal is not to replicate ancestral movement patterns, but rather to establish reference points that can guide our choices about how to exercise.

1. Ground World

“Ground World” simply means the world of movements that humans naturally perform when they are on the ground, such as squatting, sitting, crawling and rolling. Our facility with these movements derives from our quadrupedal heritage.

Hunter-gatherers spend many hours daily in Ground World - working with tools, digging for food, tending fires, preparing meals, or simply resting. They use a wide variety of stable postures for this activity, such as deep squats, kneeling, half-kneeling, cross-legged, side-sitting and long-leg sitting. Importantly, they frequently change between these postures to maintain comfort and perform ongoing work.1 These transitions may often involve crawling, as a way to reach something that is close by. Or rolling, as a way to move from lying down to standing - a useful skill when you’re resting in a savannah full of leopards and hyenas.

There's some common elements to all these ground-based movement patterns. One is that the body is in a flexed and compact posture, folded almost in half. The deep squat is the perfect example - the ankles, knees, hips and spine are near maximum flexion. Positions like this build mobility and functional strength in the legs. 

Another key challenge in Ground World is making smooth transitions between all the different postural options. Let's call this ground flow. To see it in action, look at this video from author Frank Forencich, which shows some Hadza tribe members squatting around a fire, and constantly moving between different resting positions.

Can you move like this? You could when you were younger. Children practice their ground flow for hours each day when they play with toys on the floor, or dig in a sandbox. They constantly vary their position - squatting on the heels, kneeling, crawling, and moving frequently between sitting and standing. The floor is an ideal place for them to explore movement because there is a wide base of support, lots of feedback from the ground, and no danger of falling. These activities build the foundation for good function in standing.

Most adults in modern western societies have lost their ground flow, simply because they stopped spending time on the ground. This leads to major losses in lower body mobility and functional strength. These deficiencies are revealed during activities like gardening, assembling IKEA furniture, or sitting on the floor for an extended time. Many people feel stiff, creaky and uncomfortable in these activities.

There are many forms of modern exercise that focus on ground-based movements, including Feldenkrais, yoga, animal flow, and a wide variety of mobility drills, corrective exercises, and physical therapy movements. Notably, these exercises are usually intended to serve a rehabilitative or preparatory purpose. The rationale is that when someone has lost control over basic ranges of motion in the lower body or spine, the ground is the best place to reclaim them. This fits in well with the evolutionary and developmental perspective - proficiency in ground-based movements is the foundation for moving well on two feet.  

In modern gyms, Ground World is poorly represented - it’s usually a small mat somewhere off in the corner. Fortunately, you don’t need a gym to start spending more time on the floor and doing the ground-based exercises in this book. Nor do you need to expend much energy. You just need to get off the couch.

2. Tree World

“Tree World” means the collection of movements that humans make while in trees, such as hanging, reaching and vertical climbing. Ethnographic studies show that most hunter-gatherers climb several times a week to get foods like honey and fruit.2

Children are natural climbers and will generally climb anything that can be climbed. They don't need to be taught or encouraged to develop proficiency. Even infants can grip and briefly hang from supports. 

Although there are a huge variety of climbing techniques, they all share something in common - moving body weight up or down against the force of gravity, often with poor leverage, through compound joint movements of the arms and legs. These mostly involve:

• Pulling with the arms in variable directions (e.g. pull-up or rowing motions)

• Pressing with the arms in variable directions (e.g. dip or pushup motions)

• Step-up, squat, or hip thrust/curling movements with the legs. 

• Isometrically abducting or adducting the arms for stability.

These movements require simultaneous activity of the upper and lower body, which means the core muscles must work hard to provide coordination and balance. We can therefore think of climbing as nature's full-body strength workout.

Another skill in climbing is lengthening the body vertically, to facilitate overhead reaching. This requires extending every joint from the toes to the finger tips and stabilizing the body in that extended position. In other words, climbing makes you better at getting long and strong. In this regard, it's the opposite of Ground World, which is about being short and mobile.

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The forms of modern exercise that most closely mirror the kinds of movements we evolved to do in trees would be those which challenge us to control our body weight with full-body strength, especially in extended postures, such as gymnastics, yoga, calisthenics, rock-climbing and bodyweight strength exercise. It is notable that several of these methods are considered to be good ways to develop general athletic capacities that provide a solid foundation for a variety of sports.

Tree World is not well-represented in modern gyms, but it was not always this way. Check out this pic of an old-timey gymnasium, which offers numerous affordances for climbing movements.

Many forms of resistance training replicate the basic compound joint movements used in climbing. Pull-downs, rows, presses, step-ups, and squats are obvious examples. These movements are an excellent way to get many of the benefits of climbing without the downsides of having to find a tree, or possibly fall out of a tree and kill yourself. The difference is that these gym movements involve less variability and full-body coordination.

By contrast, climbing movements always involve both the upper and lower body. For example, pulling with one arm is frequently coordinated with pushing of the opposite side leg, a movement rarely seen in the gym. Fortunately, this movement and other simple body weight challenges are easy to reproduce without a tree, and with a minimum of equipment, such as a box, pull-up bar, and TRX straps. I will provide numerous examples of similar exercises in the climbing section. Most can be done at home.

3. Bipedal World

“Bipedal World” encompasses the fundamental locomotive movements for humans: walking, running, jumping, and pursuit/avoidance (agility). A typical day in the life of a hunter-gatherer will likely involve some amount of each of these movements, developing a wide range of fitness qualities.

High volumes of walking develop metabolic health. Moderate volumes of running at slow pace and short bursts at high pace build cardiovascular health and fitness. Very brief amounts of sprinting or jumping develop power. Constantly navigating variable terrain while walking, and occasionally moving at high speed to avoid or pursue animals builds agility.

Children also show highly variable patterns of locomotion. Every day brings jumps, games of tag, lots of slow walking and movement, and occasional bursts of higher speed. No dramatic huffing and puffing, just lots of varied activity throughout the day.

The modern approach to training the fitness qualities of Bipedal World tends to differ in several respects. It is generally lower volume and higher intensity, because people have less time to exercise. It is also less variable and more specialized, with the prototypical example being someone who runs at the same moderate pace, for the same distance, on flat surfaces, every day. For athletes who include a variety of locomotive challenges in their program, they are often compartmentalized. Long slow distance one day, sprints on another, agility in a separate session. This might be highly effective for measuring progress, but also makes planning complex, and often leads people to focus on one quality while ignoring others.

Another feature of modern exercise is the ability to separate the physiological from the musculoskeletal demands of locomotion, through equipment like bikes, elliptical machines, or stairmasters. This allows people to obtain the cardiovascular benefits of bipedal locomotion while sparing their joints the stress of running. This is a wonderful thing! For example, as far as the heart and lungs are concerned, biking is Bipedal World.

These modern methods for training locomotive abilities are often good choices given modern time and environmental constraints. But recognizing the differences from natural movement patterns helps us identify ways to make improvements.

For example, people focused on intense exercise may fail to include walking as part of their exercise plan, simply because they don't appreciate its unique benefits. In some cases, going for a relaxing walk would be more productive than another round of sprints. Conversely, people who don't consider themselves athletes often underrate the benefits of doing at least the easiest versions of more intense movements like jumps and sprints, which are often avoided completely.

You don't need to visit a gym to access Bipedal World, you just need to step outside.

4. Tool world

Tool World is not defined by a physical environment, but by our intention to move objects.3 In ancestral settings, the key movements are lifting, carrying, throwing, digging, chopping, and cutting.4

These movements build on the foundation of more primal patterns. Carrying is essentially loaded walking. Lifting is standing from a squat plus the “tree movement” of pulling with the arms. Throwing or chopping movements combine compound joint pushing movements of the arm (developed for climbing and crawling) with the rotational movements of bipedal gait.

These are diverse movements but share some common elements. First, they require work from the hands, naturally building grip strength, which is strongly associated with overall strength and mortality.5

Second, tool movements tend to be high frequency and therefore low intensity. Thus, lifting rarely involves the near maximum efforts seen in gyms with barbells - there's little reason to lift something you can't carry for a distance.

Third, tool movements often involve skill, and therefore challenge the mind as much as the body. Tellingly, when kids play with objects on a playground, such as sticks for digging or swordplay, or rocks for throwing, they are challenging their skill, not their strength.

In modern gyms we see different patterns in the way people move objects. Lifts tend to be relatively high intensity and low volume. Many spare the grip in favor of working the "target" muscles. Barbells are moved at weights that would be unliftable in natural settings that don't provide objects with convenient grips.

While these modern approaches excel at building strength efficiently within time constraints, the ancestral pattern suggests they are probably not compulsory. Instead, you can build a healthy level of functional strength by climbing movements, or taking advantage of the many opportunities for handling heavy objects that are available at home—carrying groceries up stairs, working in the garden, or using simple equipment like kettlebells or sandbags.

Summary and takeaways

The “four worlds” idea gives us a rough but simple way to categorize natural human movement patterns. A typical ancestral movement “diet” probably looked something like this: several hours daily in various ground positions, 5-10 miles of locomotion at varied speeds (some of it while carrying moderate loads), climbing activities 2-3 times per week, and working with the hands throughout the day.

Children naturally gravitate toward a similar balance between the different worlds, and this can be seen by looking at the layout of a playground. The sandbox is for ground flow, the monkey bars and climbing structures are “trees”, the open space is for varied locomotion, and there are sticks, balls, toys and rocks for work on manual skills.

These activities create complementary fitness benefits: ground movements develop lower body and spinal mobility in flexed positions; tree movements build upper body mobility in extended positions and full body strength; bipedal movements provide comprehensive conditioning across all energy systems; and tool use adds functional challenge while developing grip strength. Perhaps most importantly, physical activity is distributed at low intensity throughout the day, not confined to a narrow window of extreme exertion.

We don’t need to replicate these patterns to be healthy. In fact, humans are remarkably adaptable creatures who can flourish under diverse circumstances. Further, modern environments offer many advantages over African savannas, and gyms provide safe, efficient opportunities for movement that are clearly preferable to many ancestral challenges.

That being said, ancestral patterns of movement provide a useful reference point that can help you decide how to make beneficial adjustments to your current exercise plan, by adding exercises that are missing, de-prioritizing less essential exercises, or reclaiming lost abilities through regression to more fundamental worlds of movement.

Further, connecting movement to environment helps you become more aware of movement opportunities throughout your day. As you explore each primal movement pattern in subsequent chapters, consider where you might practice them in your daily environment. Creating these associations between places and movements helps establish consistent habits.

The chapters ahead will examine each world in detail, beginning with the most fundamental: movements performed close to the ground. Ground-based patterns form the foundation for everything else we do, yet they're often the most neglected in modern life. Fortunately, they're also the easiest to begin practicing immediately—no equipment required, just a willingness to get reacquainted with the floor.

We’ll start with rolling, one of the simplest movements possible. Expect a chapter on this movement along with exercises soon.

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Footnotes

In the Introduction, we discussed the idea that the healthiest movements for human animals are most likely those movements that the body is well-adapted to perform. To understand the process of adaptation over time, this chapter will examine the evolutionary history that shaped our bodies over millions of years.

Before doing so, I can’t resist sharing some of my favorite quotes about the value of learning history:

• “People are trapped in history and history is trapped in them.” - James Baldwin, author

• “If you don't know history, you are a leaf that doesn't know it is part of a tree.” - Michael Crichton, author

• “Everything is the way it is because it got that way.” - D’Arcy Wentworth Thompson, biologist.

• “Nothing in biology makes sense except in light of evolution.” - Theodosius Dobzhansky, biologist.

Now that we are all suitably impressed with the wisdom and solemnity of addressing this topic, let’s examine the history of human movement. It's about 400 million years long, so I promise I will stick to the highlights. Why go back so far? When you zoom out, you can see patterns that are invisible when you look up close. 

Evolutionary History

The basic skeletal layout for human beings - head at one end, tail on the other, and a stack of flexible vertebrae and ribs connecting them - originated with fish in the ocean about 525 million years ago. The most important movement for fish is side-bending of the spine in an oscillating wave-like pattern. This moves the tail left and right and powers the fish forward through water. The fins on the sides don’t provide any forward propulsion, they are just there for steering.

On the ground

The fins started contributing to forward movement about 350 million years ago, when the first amphibians started “walking” in shallow water, and then a few feet onto land. They used their fins as primitive limbs to elevate their bellies just a little bit from the ground, as if they were doing a mini-pushup.

Although their limbs were primitive, they created a basic blueprint which is now shared by every four-limbed animal (tetrapod) on earth: one upper bone connecting to two middle bones, connecting to many small bones, connecting to five rays or digits. This fundamental pattern remains evident in creatures as diverse as bats, whales, horses, and humans, though modified for different purposes.

Reptiles evolved from the amphibians, and they walked over land using the same side-bending spinal movement patterns as fish. Picture how an alligator walks: belly low to the ground, limbs splayed out the sides, with each forward step assisted by a sidewinding movement of the spine.

A critical shift occurred with the evolution of mammals. Their limbs moved directly under the body, supporting weight more efficiently. With bellies lifted from the ground, limbs could reach more directly forward and back instead of out to the sides.

The spine could now assist locomotion more through flexion and extension (arching and rounding) rather than side-bending. This more powerful pattern is visible in a cheetah's sprint—its spine alternately arches and rounds as legs surge forward and back.

Interestingly, the shift to a flexion/extension based pattern of spinal movement in

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Introduction: what human bodies are for

What is a human body for? One good answer is … whatever you want to use it for. We're free to use our bodies however we choose—to dance, chop wood, run marathons, sit in front of screens, or stand on our heads.

But there is another way to answer the question about what human bodies are for, and this answer is more informative if we want to understand what kinds of physical activities will make our bodies functional and healthy. This answer is based on an evolutionary perspective which applies to all animals: human bodies, like those of any other animal, evolved to move from place to place within an ecological niche to gather food, find shelter, avoid predators, and survive long enough to pass genes to the next generation. More specifically, human bodies evolved to enable: standing tall on two legs; walking, running, and occasionally sprinting; reaching for and manipulating objects with our hands; jumping, climbing, crawling, and scrambling; carrying loads with our arms; making tools and throwing things. And sitting on the ground for hours, chatting with friends around the fire.

Primal movements

This book is about primal movements—fundamental patterns like walking, climbing, squatting, jumping, reaching, and throwing that our bodies have been adapting to perform efficiently for millions of years. The word "primal" carries two meanings: "essential or fundamental" and "related to an early period of development." Both definitions matter for this book, which makes two interconnected arguments:

1. Primal movements provide the greatest return on investment for exercise. They offer the highest benefit-to-cost ratio in terms of fitness, health, ease of learning, accessibility, safety, transfer to functional activities, and intrinsic meaning.

2. To truly understand human movement, we must examine how it developed through both evolutionary history and child development. By studying how movement patterns emerged across millions of years and how they unfold as children grow, we gain insights into many questions about how to exercise, including:

• which movements are foundational and which are more specialized;

• how different movement patterns relate to each other;

• the order in which to progress movement capacities or recover lost ones.

In short, we get a simple way to make decisions about which movements are essential, which are optional, and which should be approached with caution. Perhaps most importantly, learning about primal movements provides fascinating insight into what it means to be human on the physical level, something that becomes harder to discern as the world becomes more virtual.

The orphaned animal

Consider a brief thought experiment:

Imagine finding an orphaned animal—let's call him Brian. You decide to keep Brian as a pet and you want him to be as healthy and happy as possible. To do that, you need to ask: what kinds of physical activity does Brian need? You know all animals require exercise for optimal physical and mental health. But there are many different ways for an animal to move, and what's healthy for one species might be detrimental for another.

Is it best for Brian to walk, run, climb, or swim? Does he need to chew on hard objects for dental health, or scratch for healthy claws? Are there activities he instinctively craves, like wrestling, hunting, or digging? And how often should Brian be active? Some animals sleep most of the day and sprint around briefly at high intensity, while others move slowly at low intensity for extended periods.

The easiest way to answer these questions is to study the physical lifestyles of similar animals in their natural environment. After some quick research, you learn that animals of Brian's species typically walk about 5 miles daily, occasionally engage in vigorous play and roughhousing with their friends, spend some time climbing trees, and otherwise sit and nap. So you take Brian for walks, let him play with your dog, and build him a jungle gym. Brian thrives with this new program, and thanks you for it. 

Perhaps you see where I'm going here. Like Brian, we humans have been removed from our natural habitat. We need physical activity to be healthy and happy. But we rarely ask: what are healthy movements for human animals? This question could help us design common sense exercise programs with minimal research and analysis, yet we seldom think this way. Why not?

One reason is that discovering the natural ways for humans to move is not so easy when we live in such unnatural environments. To learn how Brian should move, we simply observed other members of his species. But when we observe modern humans, we see them hunched over screens, driving cars, slouching in recliners, or walking in high-heeled shoes. When they exercise, we see a huge and confusing variety of movements that bear little relationship to everyday activities, many of which require coaches or specialized machinery. This offers little insight into the movements that human animals are designed for. In fact, the modern environment makes it easy to forget we are animals at all.

To give us some perspective, three valuable sources of information can help:

First, we can study the physical activity patterns of hunter-gatherers, whose lifestyles more closely resemble our ancestral conditions. This should give us a rough idea of the kinds and amounts of physical stresses that promote health and good function in human bodies.

Second, we can observe how young children naturally develop movement skills in a predictable sequence. This reveals the order in which different movement capacities develop.

Third, we can examine the evolutionary history of different movement patterns—how they emerged, what survival advantages they provided, and how they shaped our anatomy over millions of years.

Together, these perspectives give us more information about which movement patterns are essential, which are optional, and how they all relate to each other. Note that this framework complements rather than replaces other forms of evidence about how to exercise. In this regard, the evolutionary lens serves two key functions:

First, it helps organize the otherwise overwhelming amount of highly specialized information about exercise that we may get from the media. For example, scientific studies tend to focus on narrow questions like the short-term effects of one specific exercise on one specific outcome. Each bit of evidence is like a single puzzle piece, with no indication of how the pieces fit together. An evolutionary perspective provides a big picture that helps us arrange these pieces into a coherent whole.

Second, the evolutionary perspective helps us filter out misinformation, which is often presented in the form of absolute claims that there is an exercise that you MUST DO or MUST NOT DO. Such claims can often be evaluated by simply asking: Does this movement pattern appear in hunter-gatherer societies? Do children naturally perform versions of it while developing? Did our evolutionary history select for the ability to perform it?

Just as understanding Brian's natural behavior patterns helped determine his exercise needs, understanding human evolutionary history provides a simple way to navigate complex exercise questions such as: Should we prioritize strength or endurance? Are machines better than free weights or bodyweight exercises? Should we do short intense workouts or long slow ones? Is sitting really "killing us"? What's the most efficient way to improve posture and build functional movement patterns? 

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What this book is (and isn't)

This book isn't suggesting that we need to pretend to be cavemen to be healthy! Nor does it imply that gym-based programs aren't excellent for developing health and fitness. Instead, it's about developing a big-picture, common-sense view of exercise that makes it easier to spot misinformation and make decisions about what kind of physical activity to prioritize.

Further, this book will not provide cookie-cutter recipes or blueprints. In fact, one of the key lessons from studying human movement is its tremendous versatility and adaptability. Humans have the largest movement vocabulary of any animal, and the greatest capacity to thrive in a wide variety of environments. With that in mind, the book is less about providing specific directions and more about offering a broad map of the human movement landscape that helps you recognize where you are and identify directions of interest. Some exploration is necessary!

How This Book Is Organized

Most of the book is comprised of chapters that address individual movements, such as running, squatting, and reaching. 

Each chapter follows a consistent format, starting with the evolutionary and developmental context of the movements, then offering a variety of exercises at varying levels of difficulty to practice them. We'll also consider similarities and differences between the primal movements as they occur in natural environments versus how similar movements are trained in the gym.

For example, in the chapter on reaching, we'll cover how human shoulder mobility evolved during our ancestors' arboreal phase, the connection between overhead reaching and vertical posture, and the critical role that reaching plays in infant motor development.

In the chapter on squatting, we'll look at how the triple extension pattern of pushing away from the ground has been present in vertebrates since they transitioned from water to land, how this pattern forms a fundamental building block for running and jumping, and how infants learn to squat from the ground up, not from standing down.

The chapters on individual movements are sequenced in a rough order reflecting how these movements emerged on the evolutionary timeline. This structure reveals important relationships—older patterns generally serve as building blocks for newer ones, offering a natural framework for progressing movement skills and regressing them for recovery of lost capacities.

To establish this timeline, the first chapter provides a "History of Human Movement" that traces our physical evolution from fish in water, to amphibians pushing away from the ground, to primates navigating tree branches, and finally to humans walking upright. We'll examine how a similar progression unfolds as babies learn to move. The rest of the book is divided into four sections that reflect the major transitions discussed in the history:

"On the Ground" covers rolling, crawling, sitting and squatting - movements related to the earliest periods of evolution and infant development that form building blocks for more complex patterns. 

"In the Trees" examines reaching, hanging, and climbing—movements that developed when our ancestors lived in arboreal environments. (And no, you don't need an actual tree to practice these!) 

"On Our Feet" focuses on bipedal locomotion: walking, running, jumping, and evasion/pursuit. These movements form the basis for most sports, as well as exercises that build aerobic endurance, speed, and agility. 

"Using Tools" addresses movements made possible when bipedalism freed our hands: lifting, carrying, throwing, and manipulating objects. These tend to promote full body strength and power. 

The final chapter shows how to combine these movements into a coherent program tailored to individual needs, addressing each component of fitness and health. Drawing on evidence from hunter-gatherer movement patterns and activity levels, it presents recommendations about a balanced movement “diet”—identifying essential movement "nutrients" and their optimal “dosage.” These guidelines are compared with contemporary exercise frameworks, epidemiological research, and conventional fitness approaches to highlight commonalities and differences. You can use this information as a way to identify and cure any “deficiencies” in your movement diet, which is the easiest way to make quick improvements.

An appendix covers theoretical concepts from evolutionary biology that provide the scientific basis for the book's approach, including adaptation, natural selection, tradeoffs, and evolutionary mismatches. Here we'll explore deeper questions about what it means for humans to be "adapted" to perform certain movements.

A final note before we begin. This book isn't just about making your body more fit and healthy - it's also about finding a sense of meaning in exercise. Modern humans are very interested in self-discovery, but our explorations tend to be limited to highly cognitive domains like literature, history, or movies. We tend to neglect the vast oceans of information about human nature that are embedded in our bodies and revealed through our movements and physical perceptions. 

When you perform movements your body is well-adapted to do —such as swinging from a branch, sprinting across open ground, or jumping over an obstacle—you experience a visceral sense of competence and satisfaction. You’re connecting with patterns of organization that have persisted for millions of years. In essence, you are gaining an embodied understanding of what human bodies are “for.”

Keep this in mind as we explore the History of Human Movement in the next chapter, arriving in the next ten days. To read it, make sure to become a paid subscriber.  [Update - the first chapter has been published.] 

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Thanks for reading. Let me know what you think in the comments - your feedback will help shape the content of the book.

The book is about primal movement patterns like squatting, crawling, hanging, climbing, jumping, rolling, carrying, and reaching. Each chapter addresses a different movement, provides exercises showing how to explore the movement, and analyzes the movement from both evolutionary and child developmental perspectives.

Rather than waiting another year or more to publish the completed book, I've decided on a different approach: I'll be serializing it here on Substack.

This means you’ll get to read chapters as they are written, engage with the material, and even help shape the final version through feedback. Once the book is complete, I will refine the content and release it as a formal book on Amazon. As a thank you, anyone whose subscription payments during serialization equal the print book’s price can request a free digital copy.

The first chapter will arrive in your inbox next week, with new chapters following each month.

What This Book Is About

Healthy Movements for Human Animals makes two key arguments:

1. Primal movements provide the greatest return on investment for exercise. They offer the highest benefit-to-cost ratio in terms of fitness, health, ease of access, safety, transfer to functional activities, and intrinsic meaning.

2. Evolutionary and developmental perspectives offer profound insights. They build a big-picture framework that helps us make sense of conflicting exercise advice, separate evidence from myth, and focus on what truly matters.

Each chapter provides practical exercises for a specific primal movement (e.g. crawling, squatting, hanging), along with insights from:

• Evolutionary biology: How the movement pattern evolved over time and why it was favored by natural selection.

• Developmental sequence: How and when children naturally acquire the movement.

• Hunter-gatherer anthropology: How the movement relates to the daily lives of people living natural lifestyles.

• Function: How the movement forms a building block for physical activities used in everyday life or sport.

The final chapter is about combining these movements into an overall fitness program, and prioritizing the movements based on your needs and interests.

This book isn't about pretending to be a caveman! Nor is it about ignoring the benefits of modern gym-based workouts or more conventional approaches to exercise. Instead, it's about forming a big-picture perspective that helps you make sense of an otherwise overwhelming amount of detail concerning how to exercise. And about giving you some fun and effective ways to expand your movement practice.

For more detail on the contents, see the draft Table of Contents at the end of the post.

How This Will Work on Substack

• Monthly releases: I'll publish a new chapter approximately once a month, each exploring a different primal movement in depth.

• Bonus content: Paid subscribers will also receive additional material that won't make it into the final book, including video demonstrations of exercises and answers to reader questions.

• Subscribe for access: The first chapter will be free, with all subsequent chapters available to paid subscribers only. If you are already a paid subscriber you are all set.

• Images: For the serialized chapters, I'll include basic photos demonstrating the exercises (likely just me in my basement). The final book will feature professional photos of someone better looking and more athletic.

• Regular content: I'll continue to post about other movement and pain science topics, though somewhat less frequently.

• Final publication: Once all chapters are released, I'll refine the content based on your feedback and publish the complete book. Anyone whose subscription payments during serialization equal the print book’s price can request a free digital copy.

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How You Can Get Involved

• Subscribe: Become a paid subscriber ($7/month or $70/year) to access all chapters and supplemental materials.

• Provide feedback: Share your thoughts, questions, and experiences in the comments section to help shape the final product.

• Spread the word: If you know others interested in these topics, let them know. Note that you can earn a free month of access by referring ten people.

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Thanks for being part of a community that values thoughtful, evidence-based and playful approaches to movement and health.

I am very psyched to get started. The introduction will arrive in your inbox next week, with Chapter 1 ("The History of Human Movement") following a few weeks later.

-Todd

Proposed Table of Contents

Introduction - An evolutionary and developmental perspective on exercise for performance and health. And some caveats about naturalistic fallacies.

Chapter 1: The History of Human Movement - The evolution of movement patterns from fish to amphibians to primates to humans. And some parallels to infant development.

Part One: On the Ground - The most primal movements

• Chapter 2: Rolling - Primal postural training.

• Chapter 3: Crawling - The foundation of locomotion, core stability, and coordinating the arms with the legs.

• Chapter 4: Sitting (on the ground) - The only static stretching you need.

• Chapter 5: Squatting - Triple extension and the fundamentals of pushing with the legs.

Part Two: In the Trees - Mobile shoulders, upright spines and four hands

• Chapter 6: Reaching - The foundation of coordinated mobility.

• Chapter 7: Hanging and swinging - The fundamentals of pulling.

• Chapter 8: Climbing - Pushing and pulling with the upper and lower body.

Part Three: On Your Feet - The challenges and benefits of bipedal locomotion

• Chapter 9: Walking - The best exercise for humans.

• Chapter 10: Jumping - Ballistic triple extension.

• Chapter 11: Running - Born to run? The fundamentals of aerobic endurance.

• Chapter 12: Pursuit/Avoidance - The fundamentals of agility.

Part Four: Using Tools - New jobs for free hands

• Chapter 13: Lifting and carrying - Putting the free arms to work.

• Chapter 14: Throwing - A uniquely human skill.

• Chapter 15: Tool use - Connecting the hands and the mind.

Chapter 16: A Primal Movement Fitness Plan - Movement as nutrition, identifying deficiencies, and developing a balanced movement “diet.”

Appendix: A discussion of theoretical issues like adaptation, trade-offs, evolutionary mismatch, and naturalistic fallacies.

Suggestions for additional content are welcome!

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A similar withdrawal reflex protects our feet, but with an important difference. If you step down onto something dangerous, and then immediately withdraw the foot away from the danger, you're going to fall. The solution is to find support from the opposite leg by quickly extending it. This pattern - flexion of one leg with extension of the other - is known as the crossed extensor reflex.

Here's how the reflex works to protect you from what some claim is one of life’s great pains: stepping on a Lego. Within milliseconds of making contact, your affected foot rapidly retracts to your center by “triple” flexion at the hip, knee, and ankle. Almost immediately thereafter, your opposite leg performs a triple extension to push into the floor, support your body weight, and maintain balance. This happens far faster than you can think about it.

You could try this for yourself, although it's kind of hard to do it on purpose. Step your right foot down onto an imaginary sharp object and then try to immediately withdraw the foot. You'll feel the left leg extend to the ground for support.

The stumble reflex has a similar pattern, also involving flexion of one leg and extension of the other, but it happens in a different part of the gait cycle. Imagine walking and then your right foot trips on a rock. You will fall on your face if you don't take quick protective action. The stumble reflex quickly lifts the foot up over the obstacle, which also serves to drive the foot forward in a lunging action to prevent the fall. At the same time, the left leg is powerfully extending to keep your center of mass high.

Why Study Reflexes?

Reflexes are interesting because they reveal something about how the body coordinates its movements on a fundamental level, and balances considerations of protection with performance.

For example, consider the pattern of movement involved in the hand-on-the-hot-stove example: the danger was encountered because the hand extended away from the body, and the hand was protected by retracting it to the body. This pattern – extension away from the center of the body for exploration, and then flexion for protection – is a fundamental part of the movement behavior of even the simplest organisms. There is something primally protective about flexion (think fetal position) and something inherently bold about extension. Movement that is safe and functional is always striking a balance.

Another key fact about protective reflexes is that they form the fundamental building blocks for basic movements. The crossed extensor reflex is the pattern for walking, running and sprinting. With each step you take, you're flexing one leg while extending the other.

The stumble reflex is involved in sprint acceleration. When a sprinter launches from the blocks, they are almost falling onto their face. This activates the stumble reflex, creating the powerful knee drive and back foot push that is necessary to catch the fall.

The “Lego-movement” of quickly withdrawing a foot from the ground appears constantly in sports that require “quick feet”, such as basketball, soccer or tennis. In these dynamic environments, athletes are constantly perceiving that one of their feet needs to be repositioned. In essence, the foot has landed or is about to land in the “wrong” place. This activates the flexors of that foot to quickly remove it from the ground or redirect it to a better place. The extensors of the opposite leg must activate quickly provide the support to allow this to happen.

When athletes attempt to develop quick feet through agility ladder drills, they're basically stepping on and off Legos in choreographed patterns as fast as possible.

Practical Applications

So what can we do with this information? Here are some practical points, mostly related to training for sport.

Flexion is underrated

Triple extension tends to get all the credit for athletic movements, because it does the work of driving the body where it needs to go. And therefore athletes in the gym tend to spend a lot of time training the posterior chain and knee extensors.

Flexion patterns tend to get neglected, and perhaps this is a mistake because the speed of flexion might act as a governor on the speed of extension, given that these are paired movements, and that protection is a high priority. Indeed, in the protective reflexes described above, flexion occurs slightly prior to extension.

In sprint technique, a common error is prolonged contact time of the foot, along with prolonged extension of the support leg behind the runner, and slow movement into lifting of the foot and knee. Research shows that improving "front side mechanics" — by shortening ground contact time and lifting the knee earlier — can enhance speed and reduce the risk of hamstring injury. The biomechanical details are fairly complex, but there is a relatively simple takeaway: quick flexion matters. Here are some technical resources making this point: a study, an article, and a video.

Use Reciprocal Facilitation

Since flexion of one leg facilitates extension of the other, you can enhance performance of either movement by cueing its opposite.

In a step-up exercise, the quality of the push by the supporting leg (using triple-extension) can be improved by focusing on lifting the opposite knee (triple flexion).

The reverse is also true - a marching or running drill seeking good knee lift could be improved by focusing on the quality of the supporting leg pushing into the ground.

Protective cues

For agility drills requiring quick foot movement, visualization cues like "imagine stepping on a Lego" might access reflexive pathways that produce faster responses.

For sprinting, some coaches cue runners to imagine running over hot coals to promote shorter ground contact times and better front side mechanics.

Allowing the body to fall forward a little bit is a good way to activate the stumble reflex. There are lots of variations on how you can break the fall: by pressing the hand or the stumbling foot into a wall (easy); accelerating into a sprint (harder); or quickly decelerating by reaching the stumbling foot into a lunge (hardest!).

Thank about bigger patterns

Other fundamental movement patterns are built around these reflexes as well, such as the contralateral movement of the arms during running, and the “hip lock” pattern of muscle activation described by Frans Bosch. The hip lock involves muscles on all sides of the pelvis working to pull it up on the side of the flexing leg (QL and abs) and down on the side of the extending leg (glute med and hamstrings.) You can find many videos demonstrating varieties of hip lock exercises here.

Try to think of how you can use hip lock style movement patterns in supine or prone. There are many! If you'd like me to film a video of some, let me know in the comments.

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We discussed Adam’s personal journey in developing a unique task-oriented teaching style. He explained how his early experiences with textbook-based instruction led to physical injuries and frustration, prompting him to explore alternative methods.

We also discussed a variety of topics related to motor learning, including the effects of internal versus external attention, the complexity of biomechanics, why deliberately making mistakes can be helpful, and the psychological and cultural factors inhibiting the exploration of new movement patterns.

Even if you're not interested in golf, I think you will find Adam's ideas highly relevant to any movement-based practice, in the context of either rehab or performance.

Links

Adam’s website

Adam’s book: The Practice Manual

Follow Adam on Twitter

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To answer these questions, we need to look at the science of evolutionary adaptation, which involves testable hypotheses about the functions of biological traits. In this post, I'll briefly review some of the abundant evidence showing that pain perception is an adaptive trait serving a protective function.

In the second part of the post, I will address a philosophical argument that I have sometimes seen on social media. Namely, that it is a “teleological fallacy” to claim that pain has a function or purpose. I will conclude that this argument is incorrect, because philosophical writing on this topic generally acknowledges that teleological thinking plays a useful and necessary role in biology, especially in fields related to medicine and evolution.

Adaptation and function

Claims about biological functions are fundamentally claims about evolutionary adaptation. For example, saying "the function of the eye is vision" is shorthand for a much more cumbersome statement: that natural selection, operating over millions of years, favored genetic variants that produced better-functioning eyes because improved vision helped organisms survive and reproduce. Scientists use the simpler functional language while keeping in mind the underlying evolutionary mechanisms.

It's important to note that not every biological trait is an adaptation - some are developmental byproducts (like belly buttons), vestiges of formerly useful features (like the human appendix), products of sexual selection (like a peacock's tail), or simply random genetic drift. To determine whether a trait is an adaptation shaped by natural selection to serve a particular function, scientists use several criteria.

1. Complex Organization. The trait should show evidence of intricate design well-suited for a specific function that improves fitness. For example, the lens, cornea, and retina of the eye work together in functional ways that would be extremely unlikely to arise by chance.

2. Historical Evidence. Since adaptations develop gradually, we should find evidence of earlier forms of the trait in the fossil record or in related species. In the case of the long necks on giraffes, there are fossil records showing a gradual lengthening of neck vertebrae over millions of years.

3. Cost-Benefit Analysis. The survival and reproductive benefits of the trait should outweigh its biological costs. For example, the large horns of bighorn sheep are energetically expensive to grow and carry, but their benefit in male competition for mates outweighs this cost.

Applying these criteria to pain perception reveals strong evidence for its adaptive nature. Pain protects organisms from physical danger in at least three ways: withdrawal from noxious stimuli, learning to avoid such stimuli in the future, and avoiding movements that prevent healing from injuries.

There is strong evidence that the benefits of this system outweigh its costs, most vividly illustrated by the experience of people born without pain perception, who inevitably suffer severe injuries and shortened lifespans.

Further, the biological organs which create pain perception show evidence of a complex design that is well-suited to protect the body. Nociceptors are distributed in locations and densities that optimize the detection of potential damage. The information they provide undergoes complex processing at the level of the spinal cord and the brain, which integrate other forms of information relevant to physical threat. The sensitivity of this system is constantly modulated in adaptive ways, increasing after injury, and returning to normal levels when the injury heals.

There is also evidence for the evolutionary history of pain. Even in the simplest organisms, protective withdrawal responses can be found, and these become more sophisticated over evolutionary time. In fact, even squid have nociceptive systems that become more sensitive after injury, and it has been shown experimentally that when this sensitivity is blocked by drugs, they are less likely to take evasive action in the presence of natural predators like sea bass, and more likely to get eaten.

Based on all this information, we can safely conclude that the biological organs which create pain perception in humans are adaptations favored by natural selection because they increased our ancestors’ chances for survival and reproduction. This is what it means to say that the function of pain is protection.

For more detail on the evolution of biological mechanisms related to pain perception and behavior, see this collection of academic papers presented by the Philosophical Transactions journal of the Royal Society.

Why understanding pain's function matters

So why do we care about the function of an organ? Because this helps make sense of everything we know about that organ.

Consider all of the data we can collect about the heart, the kidney, or the gastrointestinal system: their physical shape, structure, cell types, and behaviors under different circumstances. The evidence only comes together into a meaningful picture when we understand that the heart is for pumping blood, the kidney is a filter, and the gastrointestinal system is for digesting food. The functional perspective provides the macro-level picture that makes sense of the micro-level data.

With pain, knowing that it serves a protective function explains why pain pathways connect to both reflex circuits (for rapid withdrawal) and emotional centers (to make the experience memorable), why inflammation and pain work together (marking injured areas for protection), and why the dorsal horn of the spinal cord becomes more responsive after injury and returns to normal only after healing. We are not surprised to learn that it interacts with other systems which serve a protective function, such as the immune system, which fights infection and heals tissue damage, and the endocrine system, which mobilizes the stress responses which respond to emergencies.

The functional perspective has practical implications for treatment. If pain evolved for protection, we should expect that it becomes more likely in the presence of a variety of threats - not just tissue damage, but also poor sleep, emotional stress, or general poor health. Conversely, factors that promote safety and wellbeing tend to help with pain. This insight broadens treatment options beyond just focusing on affected tissues.2

Of course the evolutionary perspective on pain can only take us so far. Although it can tell us that pain is caused by activation of a system that evolved by natural selection to protect the body, it can't always tell us why it is activated in a particular case or whether that activation is actually protecting the individual.3 To answer those questions, we need other kinds of explanations, which might include physiological mechanisms, potential areas of tissue damage, and the history of the pain. The functional perspective does not replace these mechanistic or historical explanations, but instead acts as a complement that helps organize their interpretation. And when it is used in this fashion, functional explanations do not run afoul of concerns with teleological thinking in biology as explained in more detail below.

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Why teleological language in biology is not a fallacy

Teleology means explanation in reference to purposes, goals, desires, or functions. Here are some simple examples of teleological statements in biology:

• The immune system protects against infection.

• Birds migrate south for the winter to find food.

• Chlorophyll captures sunlight to make energy for plants.

• Turtles go ashore to lay their eggs.

Each statement explains a biological event by reference to purposes or goals, rather than just describing the mechanism of how it happens. Although these statements are ubiquitous in biology and have obvious practical value, their deep meaning has been a subject of debate for centuries.

Aristotle argued that natural events should be explained in terms of four causes: material cause (what something is made of), formal cause (its structure or pattern), efficient cause (what brings it about), and final cause (its purpose or end goal).

A similar framework appears in modern biology. Nobel laureate Niko Tinbergen argued that to fully understand a biological phenomenon, we must answer four distinct questions:

1. How does it work physically (mechanism, causation)

2. How did it develop from embryonic tissue? (ontogeny, development)

3. What is it for? (function, adaptation)

4. How did it evolve? (phylogeny, evolution)

Note that function is explicitly mentioned in the third question, and is implied by the fourth. The idea that biology requires explanation on many different levels appears in other forms. Evolutionary biologists distinguish between proximate explanations (immediate mechanisms) and ultimate explanations (evolutionary functions). The biopsychosocial model states that a full understanding of health and disease requires biological, psychological, and social perspectives. And of course there is Dobzhansky's famous claim that "nothing in biology makes sense except in the light of evolution."

So why might it be a problem to use teleological language in biology? Historically, biologists have been wary of using teleological language for two reasons: they don’t want to sound like they are advocating for either (1) intelligent design or (2) vitalism.

Before Darwin, theologists like William Paley argued that complex biological function was evidence of a divine creator. The argument was essentially that design requires a designer. After Darwin showed how complex function could arise without conscious design, scientists were cautious about using language that might suggest intentional design. For example, they might choose to use the phrase “appearance of design” instead of “design.”4

Another historical reason for avoiding teleological language was its connection with vitalism - the idea that biological phenomena could be explained by non-material "vital forces" rather than physical mechanisms. Since vitalism denied that life could be explained through physics and chemistry, it stood in opposition to scientific progress.

Modern functional explanations in biology avoid these errors. When biologists say "the function of the heart is to pump blood," they don’t mean the heart works by magic, or that it was designed by a god. Instead, they’re using common-sense language that refers to the effects of natural selection on adaptive traits. Furthermore, functional explanations don't compete with mechanical ones - they complement them. Understanding that pain serves a protective function doesn't prevent us from studying its molecular and neural mechanisms. Rather, it helps organize our understanding of how these mechanisms work together.5

It is for these reasons that philosophers generally agree that functional analysis in biology is both desirable and necessary. Although there are many ways of reaching this conclusion, a good summary can be found in the Stanford Encyclopedia of Philosophy, which is a useful resource for examining the breadth and depth of philosophical thinking on any particular issue. The article on Teleological Notions in Biology states in the opening paragraph that teleological explanations play "an important explanatory role" and are in fact “ineliminable” in fields like "evolutionary biology, genetics, medicine6, ethology, and psychiatry."7

Wrapping up

There's nothing with wrong talking about the function of pain, as long as it's not used as a way to avoid explaining the physiological mechanisms that execute the function. In fact, using functional perspectives is one of the best ways to develop simple, accurate and practical ways to summarize large amounts of technical information for yourself and clients.

If you are interested in the nuances or the many sub-issues related to this topic (and I hope you're not), there are many rabbit holes to go down. You can find more information in the footnotes below, the listed resources, and some related blog posts I’ve written previously.

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Related posts

Here are some blog posts that relate to the complexity of biology, evolutionary and developmental perspectives on health and disease, and using functional or intentional analysis to understand biological mechanisms.

Books and articles on the philosophy and science of evolution

Darwin’s Dangerous Idea by Dan Dennett. Probably the best book I’ve ever read.

From Bacteria to Bach and Back by Dan Dennett

The Blind Watchmaker by Richard Dawkins

Article from Michael Levin and Dan Dennett: Cognition all the way down: Biology’s next great horizon is to understand cells, tissues and organisms as agents with agendas (even if unthinking ones)

A great series of scientific papers articles on looking at pain from an evolutionary perspective.

An article in the Internet Encyclopedia on Causal Role Theories of Functional Explanation

Footnotes