Back to the Trees | Of human tree-climbing, forgotten potential, and skewed evolutionary perspective
Human tree-climbing is a skill innate to the human animal—an aspect of our physical capacity as old as our species itself. This article looks at tree-climbing in the context of our evolutionary past, set against my own observations and research experiences with the Batek tribe of Malaysia. It is a narrative exploration into the physiology and psychology of tree-climbing, including a detailed breakdown of the actual techniques themselves.
It’s a monster of an article—perhaps more of a book chapter (sorry!)—so by all means jump to the sections that interest you. And if you’re just here for a tree-climbing how-to then skip to the middle section.
EVOLUTIONARY BACKGROUND | OF LOCOMOTORY SHIFT AND A FORGOTTEN SKILL
‘Walking on two limbs instead of four has many drawbacks. It deprives us of speed and agility and all but eliminates our capacity to climb trees’
— Owen Lovejoy, 1988—
Somewhere between five and eight million years ago—the Late Miocene of Africa—our hominin ancestors came down from the trees and began walking around on two legs. Thought to have been triggered by the gradual fragmentation of forests into grasslands—aptly coined the ‘savannah hypothesis’—this hominin shift from arboreal to terrestrial locomotion has long been recognised as a major adaptive turning point in the evolution of our species.
To that end, many studies have addressed the adaptive significance of our ability to run and walk efficiently for long distances (e.g. Bramble & Lieberman, 2004), and the precise technical details of human bipedal locomotion have been continuously refined (e.g. Damavandi, Eslami, & Pearsall, 2017; Schmid, Schmidt, & Piaget, 1994).
However, the role of human arboreal locomotion, or to put it simply, tree-climbing, has been largely ignored: generally assumed to have steadily diminished in skill and relevance as our ancestors adapted to a life of habitual bipedalism.
But in fact, human tree-climbing didn’t die out. Deep in the tropical rainforests of Africa and Asia, small bands of hunter-gatherers kept this forgotten aptitude alive. Maintained and passed down for thousands of years, rainforest hunter-gatherers around the world exhibit extreme feats of tree-climbing remarkably akin to those of our cousins—the other great apes. In many of these societies, tree-climbing holds central economic and social importance, and represents a vastly under-appreciated form of human diversity, foraging capacity, and locomotor potential (Kraft, Venkataraman, & Dominy, 2014). Yet, whilst arboreal foraging is well-recorded (Devine, 1985; Endicott & Endicott, 2008), little focus has been given to the technical aspects of human tree-climbing itself.
THE BATEK OF PENINSULAR MALAYSIA | IN SEARCH OF THE TREE-CLIMBERS
Fresh out of university, and eager for adventure, I set out to find one of these tree-climbing societies myself. My goal: to live with and learn from the Batek tribe in the jungles of Peninsular Malaysia.
The Batek are famous for their unique social systems and egalitarianism, and I had studied them at length during my degree. But what interested me even more was their ability in the trees. One of the most capable tree-climbing cultures on the planet (Endicott & Endicott, 2008), the Batek of Malaysia are reported to climb to dizzying heights in pursuit of honey, fruit and arboreal prey.
After some searching I came across a small group of Batek near the town of Merapoh on the borders of Taman Negara Rainforest. Over time I integrated with the group and began to learn their language, spending more and more time with them in the jungle and their village.
It was the beginning of all manner of crazy and unexpected adventures, many of which I’ve detailed elsewhere. But for months their tree-climbing still evaded me, and I began to give up hope. Perhaps in their shift from jungle nomads to a village settlement they had lost their famed ancestral skills? But then one day I saw a glimpse.
30th July 2018
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All around me the trees are alive with children, dancing nimbly along the branches, screaming and shaking the boughs in imitation of gibbons. I can’t keep up, but climb higher to where I can watch a little better. They walk on the thinnest of branches, clutching many at a time to hold their weight. Right out into the periphery they dance, along tiny twigs and to the ends of boughs, many meters above the ground. Down below the little ones wait expectantly, peering up with open eyes. The children above eat greedily, tearing the fruits from the trees without even bothering to pick them. The remainder they detach in bunches and rain down to the waiting mouths below. On the ground tiny, naked children rip apart the rambutan, discarding the hairy cases and gorging on the pale fruit. The lower branches of the tree are stripped bare.
Unsatisfied, a ten-year-old silhouette climbs back to the central trunk. Iman climbs better than the others, bolder in his ascent. He takes the bark in hand and presses the balls of his bare feet into the vertical surface as he calmly walks, hand over foot, up the bare trunk with the ease of experience. He reaches the upper canopy and steps onto the surrounding branches, venturing out into space twenty meters above the ground. With little but a sparse network of finger-thick twigs for support, he clutches at leaves around him and tentatively tests the branches ahead. Finally, way out in the farthest reaches of the tree he retrieves his prize, a bunch of rambutan almost the size of himself. Casually he walks back to the main trunk and descends as if sliding down a fireman’s pole, draped like a leopard over a bough, his prey clutched in one fist. On the ground he takes my hand in his and we walk with the others back to the village. A wake of hairy fruit cases trails haphazardly behind.
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Forced from a traditional nomadic jungle lifestyle by the insidious spread of palm oil, Batek tree-climbing knowledge is becoming rarer, and there was no doubt that this particular group had lost much of their traditional skill. Yet, in those children’s play I saw a glimmer of hope, that perhaps, somewhere behind their day-to-day exterior, a shadow of past skill remained.
A year passed: forays into an underwater world; work across SE Asia and battles with a tropical disease. Yet I couldn’t get that image of treetop children from my mind, and, heading home to England under the debilitating clutches of leptospirosis, I vowed to return.
CHALLENGING PARADIGMS | MAKING THE CASE FOR HUMAN TREE-CLIMBING
One exception to the conventional academic view of tree-climbing’s demise is a collection of studies led by anthropologists Vivek Venkataraman and Thomas Kraft (Venkataraman, Kraft, & Dominy, 2013; Venkataraman et al., 2016; for overview see Kraft et al., 2014;). They challenged the idea that bipedal adaptations such as an arched midfoot, rigid ankle and the loss of an opposable hallux are indicative of arboreal incompetence. Instead, they showed that Twa and other forager groups were able to achieve comparative in-climb ankle flexibility to that of other great apes—it was not a case of bone structure but rather a flexibility limitation that restricted non-climbing populations.
Perhaps most notably, this research challenged the idea that we can reliably infer climbing or walking behaviour from fossil remains. No longer can we say that Australopithecus or early Homo with their characteristic bipedal ankle joint and bone structure is unable to climb well. Indeed, modern humans with even greater bipedal adaptation are climbing closely in ability to chimpanzees and orangutans. Essentially, Vivek and Tom’s research has emphasized both kinematic similarities (e.g. Figure 1) and uniquely-human differences between human and great ape tree-climbing (Kraft et al., 2014)—the latter perhaps representing practical solutions to the constraints of bipedality. After all, if you can’t grasp the tree with your flat foot, then why not lock yourself in with a layback position…
Without wanting to be overly sensationalist, this idea challenges the conventional framework of early human evolution. If we did retain our ability to climb well—which observations of rainforest foragers around the world essentially proves—then the fitness benefits of the trees (such as foraging resources, protection from predators, etc.) were maintained. Human arborealism may well have played a far larger ongoing role in hominin evolution that has previously been assumed.
Similar ankle kinematics in humans and chimpanzees during climbing. Figure from Venkataraman et al. (2013)
As chance would have it, both Vivek and Tom did their PhD research with Batek groups, working under the master Batek anthropologist himself, Kirk Endicott, known for over 40 years of work with the tribe, and the author of their defining ethnography: The Headman was a Woman. During their time in Malaysia, the pair visited the tribe I had lived with, and now, in an unexpected turn of events many years later, the Batek themselves pointed me towards them.
Contacting, and later meeting with, Vivek back in England I quickly learnt more, and was soon plotting my passage back to the jungles of Malaysia. Papers and research methods; introductions and grant applications—step-by-step my plans merged into a reality.
Straight from the cover of a NatGeo: Vivek Venkataraman and Thomas Kraft
A CHARACTERISATION OF HUMAN TREE-CLIMBING TECHNIQUES
The first job was to characterise the climbing techniques themselves. Academic literature was a good place to start, and a little digging into photographs and old ethnographies (not to mention Vivek and Tom’s excellent treatise on the subject: Kraft et al., 2014) began to reveal patterns and basic distinctions. Vivek himself generously indulged my endless questions, outlining the three main gait patterns of human tree-climbing.
However, for a true understanding I needed to see these techniques for myself, and more importantly, examine exactly what each entailed and where they were used. Literature is thin, and goes little beyond a brief description—not a single study I could find actually looked into the physical requirements or biomechanical details of the techniques. I needed to see it in the flesh.
And so it was that I returned, a little over a year since my first introductions with the group. With re-enthused resolve to discover what they could do, I redoubled effort my efforts to learn the language and integrate with the group, and before too long I began to breach the subject of tree-climbing with some of the men. One thing led to another, and within days I was finally watching the Batek scale the trees with my own eyes. What follows is a report of my observations and the information gleaned from the accounts of the Batek of Batu Jalan.
Let us begin with the language—a good start with any such research. Just as we do, the Batek have a catch-all word for tree-climbing: luwei(t). Yet, unlike us, they distinguish the act further, splitting it down into three separate categories: cheuhtwont, cuksank, and cheuhn. Albeit with different names and minor variations, a quick skim of academic literature or ethnographic photographs confirms that these same techniques are employed by human tree-climbers across globe—somewhat of a basic gait catalogue of human arboreal locomotion.
CHEUHTWONT (LAYBACK)
Cheuhtwont is perhaps the most iconic tree-climbing style—the one we envision when we picture rainforest foragers high in the canopy. Only possible on trees thin enough that the climber can reach around, when done well cheuhtwont can look effortless—almost like walking up the trunk. I can assure you however that it isn’t…
On the face of it, cheuhtwont is very similar to the technique used by chimps and other great apes. However, whilst great apes are able to grip the trunk with both foot and hand, the human non-grasping foot requires us to rely exclusively on a friction-lock that employs the opposite forces of pulling hands and pushing feet to hold us onto the substrate—much the same as a crack climber’s layback. In reality, staying in place is as much the result of the rotational force of the feet pushing into the trunk as it is a direct push-pull lock. Essentially the hand contact redirects the gravitational force of our centre of mass back into the substrate through the feet via an impressively rigid application of body tension. Trust me, you feel it in your core after only a single step.
A symmetric walking gait is then used to walk the body up the trunk, albeit with the limbs often moving one at a time—arm in advance of opposite leg.
CUKSANK (FROGGING)
Cuksank is used for larger trees, and apparently also when they’re especially slippery, or so they told me. By opening the hips and inverting the feet, one can sit down into their haunches, largely using gravity to lock the tree tight between the feet—somewhat similar to the way a perching bird mechanically clamps shut their talon when squatting down. The hands are then used together (often with fingers interlocked if the substrate is narrow enough) to reach up and pull against the trunk, momentarily taking the weight off the feet. This allows just enough time to scoot the feet higher, thus leapfrogging in an asymmetric hindlimb-forelimb gait up the trunk.
Typically cuksank requires less strength and core tension than cheuhtwont, and it is notable that many of the lesser able Batek will utilise this technique even on thinner trees. That said, it cannot compare with the speed and efficiency of a competent cheuhtwont climb, which remains the preference of the better skilled climbers. Rather, where cuksank really comes into its own is with wider diameters, and although my own Batek village have long since lost such ability, there are ethnographic photographs of climber hugging their way up substrates well over two to three feet in diameter.
CHEUHN (HALLUCAL-GRASPING)
To the Batek, cheuhn refers more to substrate than kinematics. It is the method used to climb the rattan vine. Of massive importance both economically and subsistence-wise, rattan—or aweigh as they call it—is the means to reach the canopies of trees with trunks too wide to climb.
The technique is much the same as cheuhtwont, with the major exception being the use of the big toe gap to grip the vine tight. The Batek possess far greater toe dexterity than us—most likely a product of regular use rather than any specific adaptation—allowing them to actively grip the substrate in a lateral plane, rather than simply scrunching their toes downward as we might do to pick something off the floor. Indeed I have often seen the Batek reach and grasp objects with their toes with a dexterity I couldn’t begin to replicate.
The other difference to cheuhtwont is that in cheuhn the hands too are used to grasp and hold rather than simply pull. If cheuhtwont is the tree-climbing equivalent of a layback on a crack, then cheuhn is climbing a bottom-tethered rope, using a combination of simply grasp and pull, and the friction-lock layback principle. Beyond the necessary strength required, a primary difficulty is that of staying on the higher side of the vine, and spinning off balance to the underside results in a climb of far higher effort.
A NOTE ON TECHNIQUE CONTINUITY AND VARIATION
Following from the discussion of cheuhtwont and cheuhn, it is notable that the two techniques are largely continuous, and of course the Batek will grasp a thinner tree with both hand and foot if at all possible. A frictional layback shifts to grasping rope climb not in a single gait change, but rather in degrees. Hence the Batek’s perhaps more useful delineation of the techniques as a definition of substrate rather than kinematics.
It is also notable that much variation is seen for each technique, even within individuals of the Batek, let alone across tree-climbers worldwide. For example, the use of a single foot hooked around the back of the tree during the hand-movement phase of cheuhtwont is common, as is an occasional cuksank-style rest when tired. Branches and non-vertical substrates add to the complexity of movement form, and it is notable that the techniques discussed above refer only to unbranched vertical movement. Horizontal movement is another interesting topic entirely, and I have observed many remarkable above and below branch behaviours, such as the remarkable tabbin: a gibbon-like arm-over-arm brachiation sometimes employed by the younger children.
And then we come to aided climbing—the use of vine harnesses, axe-chopped steps and foot links—an infinite variety of ingenious inventions from around the foraging globe. Interestingly the Batek themselves use little, and those of other tribal communities are beyond the scope of this article, nor do I have the authority to comment on them in depth. I will however mention the many Batek ethnographic records (alas I never saw it) of rattan vines employed to bridge the canopies many tens of meters above the forest floor.
It was a start, and a good one. I had at long last realized a dream of seeing with my own eyes the tree-climbing skill of the rainforest hunter-gatherer. Breathtakingly smooth and easy, it surpassed all expectations, even in a tribe that had likely lost much of their ancient aptitude—a powerful reminder of our species diverse physical potential. Yet there were still so many questions to be answered.
INTUITIVE PERSPECTIVE | TREE-CLIMBING PHYSIOLOGY
Enthused by the success of my previous visit, I focused my efforts on putting together an academic research methodology, and with the help of Vivek once again (for whom I cannot thank enough), I developed a seemingly watertight plan and returned to the tribe once again.
Almost immediately I hit a brick wall, and for reasons that amount to a long boring saga of delayed permits and a lack of sufficiently good climbers to fulfil an academic sample quota, traditional academic research methods and my failproof plan became impossible.
And so I switched my approach.
I have written elsewhere about the benefits of practical and intuition-led research, and that became my slant, using open-ended observation and personal experience to discover all I could. Taking my own advice, I tried out each technique myself, gradually improving the specific strength and skill until I could at least cycle through the motions of all three, granting me perspectives and movement familiarity that I could never have gained through observation and analysis alone—a physical understanding that is perhaps the most fundamental research component of all.
I returned at last one final time, this time in the company of elite running coach and human movement specialist Shane Benzie (see here for an in-depth account of our expedition)—a man known for his non-academic, yet vastly practical, research with respect to elite athletes and human movement potential.
We watched and examined the Batek move, run and climb for four days straight, and at long last, with a complete interrelated repertoire of academic literature, direct observational analysis, and personal physical experience, I began to understand what it took to realise our species’ arboreal potential.
Taking my own advice, I soon realised from my personal experiments in tree-climbing—much to the Batek’s amusement—that the level of core and overall body tension required is huge. It is no wonder these individuals possess such flawless physiques; they are honed and conditioned for a muscular endurance that cannot fail for danger of being unable to return to the ground.
The Batek physique is beneficial also in terms of its leanness. No forager wields unnecessary muscle mass since they do not possess the nutritional excess to build it in the manner of western gym goers. And yet they are stronger, like gymnasts: pure wiry musculature. And, as any rock climber will tell you, that leanness is a significant advantage. Especially so in tree-climbing, where, coupled with the Batek’s small stature and hypermobile ankles, it allows them to bring the centre of gravity in close to the tree, even in the layback position of cheuhtwont.
Hand and foot resilience is another factor, and even after many months of machete handling and walking the jungle barefoot, my hands and feet soon began to rub raw. Batek feet meanwhile are so leathery that the children will not respond to being tickled on the sole!
Perhaps most telling of all, and perhaps also the most obvious, is the general physicality of the Batek. Forged from a life in and amongst the jungle, those that still climb are the ideal in functional human body composition. They are strong, able to perform well over ten pull-ups untrained, and even hang for thirty seconds plus on a 24mm edge—something I previously assumed would be possible only for a rock-climbers abnormally-developed forearms.
Watching the Batek run and climb with their lines of fascia highlighted in kinesiology tape was a true honour and masterclass in human fluidity. Without even understanding the concepts—or perhaps as a result—the Batek climbers flowed with their artificial kinaesthetic exoskeleton—a picture of elasticity and fluidity in stark contrast to our own paradigms of biomechanical robotics.
A massive thank you to both RockTape and Fingershinder for the sponsorship of their equipment and all the insights it revealed.
CLIMBING BEYOND | TREE-CLIMBING PSYCHOLOGY
Coming away from those final days with the tree-climbers I couldn’t have been happier with how it had played out. Both Shane and I had learnt much to further our understanding of the human movement paradigm, and I had at last begun to understand the physiological profile of the Batek’s remarkable arboreality—founded as much in their wider lifestyle as it was within the skill itself.
Yet there was still something missing—something that I had long suspected may be the central factor in the Batek’s climbing proficiency. And it was something beyond my ability to experience. Whilst I could see the path to developing their physical ability, this was beyond me. And I still don’t really understand it or how it is achieved.
It is the mindset of hunter-gatherer tree-climbers that ultimately makes them so capable. On a par with that of elite extreme sports athletes, it is the same surety in ability and capacity to dissociate from emotion and future that allows the big wave surfer to ride the ocean’s giants, or the free-solo rock-climber to remain calm atop thousands of feet of empty air. I perceived only a glimpse of it within the climbing of these Batek, yet one needs only watch Human Planet’s famous sequence of the Bayaka honey hunter to see it in full.
I am no expert in human psychology, and can speak only from what little I could perceive in my time with the tribe at Batu Jalan, placed in context alongside my own dabblings in the art of free solo climbing. Yet I believe the Batek climber’s unshakeable mindset to be the result of a number of factors.
Photo by Timothy Allen (BBC)
SOCIETAL PERSPECTIVE
Fear is a product of the mind. It is not real. It is simply a projection of the mind into the future to perceive and anticipate consequence. Yet if that mind is programmed differently and consequence subsequently reframed, then fear itself is rewritten.
When Abi, a little Batek boy fell from five meters high, catching his foot in a fork on the way down, his father took one look at his wailing and turned back to the football game at hand, content that his son was alive. Abi spent the next week unable to walk. Such is the nature of the Batek community. There is no indulgence in non-serious injury or upset, and so children don’t react. They bounce rather than break; laugh rather than cry. High in trees at age five, with machetes in their teeth or at their waists, there is no health and safety. For sure it is a gamble. Generations of supremely capable adolescents justify the one occasional death or serious injury.
As is the Batek attitude to life, so too to tree climbing. Batek society does not view it with fear of consequence, and so it is not framed in such a context. A cultural perspective of plain realism does not enlarge dangers beyond their reality. People rarely fall; society does not therefore play on a reputation of danger; and thus individuals do not develop irrational (or, as it seems in some cases, any) fear of the climb. The Batek know no preconceived western limitations on climbing ability and human potential, and so nor do they abide by them.
EXPOSURE
Coupled with this is the frequency of exposure. With children climbing as high as they wish on a regular basis from the age they can walk, exposure is frequent and extreme, and thus it becomes the norm. Since this begins long before the age of logical reasoning or thought of consequence, fear and danger never really manifest, and constant exposure prevents them from growing unchecked.
ABILITY AND SELF-SURETY
And perhaps most importantly: ability. Years of constant play and refinement imbues an intimate understanding of personal ability: of balance, coordination and strength. Such self-awareness allows an accurate assessment of capability in any given scenario, and risk becomes a calculated quality. For risk itself is comprised of two components: likelihood and severity. Even if the severity is certain death, if the likelihood is next to zero since you’re so capable that the task in hand is easy, and what is more, you know and truly believe that, then risk is no longer significant nor the prospect of the climb abhorrent.
THE WHY
Confidence in ability; early and continued exposure; and a vastly different lifestyle that operates under an alternative cultural-societal paradigm of risk, safety and ability. Is it any doubt that these Batek are so mentally robust?
Yet this brings us to another pertinent question. Why do they do it at all? Batek climbers do fall and die. It is well recorded, and even in my time with the group I watched children fall from many meters high, thankfully with no permanent injuries. No longer can we suggest that tree-climbing is the result of sheer desperate need, nor ever was this likely the case, for treetop products, while an important contribution to rainforest forager economy, are not essential, and other safer-bought resources comprise a rainforest diet’s caloric majority.
Why therefore do they do it? Because they always have? Because the risks are on average outweighed by the rewards? Or, like the adventure athletes of the industrialised world, does climbing bring them fulfilment: an aliveness in flow. Or perhaps it is that the ancient act of tree-climbing serves as part of a cultural identity—a belonging in the forest and a means of touching their heritage of old?
Perhaps it is all of these things. Yet for how long I do not know. Already I see fear creeping into many of my Batek friends, and the will to climb is diminishing. And with the loss of height, frequency and ability, the mind of the master tree-climber begins to crack.
A final generation?
TREE-CLIMBING | THE ROOT OF MODERN ROCK-CLIMBING?
Yet, as the tree-climbing of old begins to fade from use and memory, I cannot help but wonder on the legacy it leaves behind. Is it simply an ancient tool of relevance only to a select few small-scale societies? Or does it embody something larger: something rooted deep in the very fabric of humankind.
We might ask, with over eight million individuals a year in the US alone cramming themselves into sweaty boxes to haul themselves up plastic walls, or another however many more million scaling rock faces around the globe for no purpose at all, only to be lowered before they even reach the top, what is it that we humans see in the art and sport of rock-climbing?
Certainly there is the physical challenge—the satisfaction of problem solving, adventure and testing our limits. And then there is the incredible climbing community that most other sports would be hard-pressed to get anywhere close to. Yet I can’t help but think that in addition to these points, or rather perhaps through them, modern rock-climbing may simply be the product of an innate human capacity and satisfaction in overcoming vertical obstacles—a subconscious nod to our ancestral aptitude for arboreal locomotion; a fulfilment of the part of the human psyche designed to climb trees.
There is no doubt that our species can be far more capable in the trees than is conventionally assumed, and that hidden in the jungles we see a potential that is not dead, nor indeed far from that of our ape brothers. Yet I wonder: perhaps that potential has never been hidden after all. Perhaps it is possible that across the world we have in fact been developing and exploring that innate human capacity all along, veiled under a different guise.
The need for food gives way to the thrill of adventure and self-discovery; bare feet against mighty tree-trunks become the friction of fingertips on ancient cliff-faces, and as Alex Honnold scales the face of Yosemite’s El Capitan for the hundredth time—this time rope-less—perhaps we see re-incarnate the long-refined physiology and unbreakable psychology that was developed millennia ago in the tree-tops of Africa. Never lost, never replaced: an age-old link to the physicality of our ancestors; a pure freedom and expression of human potential in the wilderness that is our earth.
Photos by Jimmy Chin (National Geographic); Timothy Allen (BBC)
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Devine, J. (1985). The versatility of human locomotion. American Anthropologist, 87(3), 550–570. https://doi.org/10.1525/aa.1985.87.3.02a00030
Endicott, K. M., & Endicott, K. L. (2008). The Headman was a Woman: The Gender Egalitarian Batek of Malaysia. Long Grove: Waveland Press.
Kraft, T. S., Venkataraman, V. V, & Dominy, N. J. (2014). A natural history of human tree climbing. Journal of Human Evolution, 71, 105–118. https://doi.org/10.1016/j.jhevol.2014.02.002
Lovejoy, O. C. (1988). Evolution of Human Walking. Scientific American, 259(5), 118–125. https://doi.org/10.1038/scientificamerican1188-118
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Venkataraman, V. V, Kraft, T. S., & Dominy, N. J. (2013). Tree climbing and human evolution. Proceedings of the National Academy of Sciences, 110(4), 1237–1242. https://doi.org/10.1073/pnas.1208717110
Vivek V. Venkataraman, Thomas S. Kraft, Jeremy M. DeSilva, & Nathaniel J. Dominy. (2016). Phenotypic Plasticity of Climbing-Related Traits in the Ankle Joint of Great Apes and Rainforest Hunter-Gatherers. Human Biology, 85(1–3), 309. https://doi.org/10.13110/humanbiology.85.1-3.0309