The Hairless Ape

Originally published in 15 February 2025 on Substack https://substack.com/home/post/p-158762719

Let’s continue with the evolution of our own species. Around six million years ago, a group of apes found themselves living in a shrinking rainforest. Scientifically, these creatures belonged to the family known as great apes, or Hominidae, which today still includes humans, chimpanzees, gorillas, and orangutangs. These apes, who had evolved to live primarily on fruit and sought refuge from predators by climbing trees, eventually found their environment transforming into much dryer woodland savanna.

Forced to adapt, they began gathering new types of food, such as tubers and roots, rather than the fruits they once relied on. This shift required them to cover greater distances on the ground and use digging sticks to extract underground food sources. Identifying edible roots was no simple task—it demanded a new level of intelligence, as the only visible clues were the stems and leaves above ground.

Millions of years passed and these once rainforest-dwelling primates evolved into master survivors of the African savanna, where acquiring food required ingenuity and adaptability. About four million years after their exodus from the rainforest, they had already become almost entirely hairless, dark-skinned, and fully bipedal members of the genus Homo. The only significant body hair remained on the top of their heads, shielding them from the sun’s harsh rays.

Approximately two million years ago, a new species emerged—Homo erectus, the ”upright human.” Their survival and success on the West African savanna was unparalleled. Homo erectus was the first human species to resemble us in many ways. They stood between 145-185 cm tall and weighed between 40-70 kg. Unlike their ape ancestors, there was little size difference between males and females. Their near-complete hairlessness likely stemmed from four main reasons:

1. Warmer nights meant body hair was no longer essential for insulation.

2. The activation of the melanocortin-1 receptor darkened their skin, providing protection from harmful ultraviolet rays, eliminating the need for fur as a shield against sunburn.

3. Most importantly, they developed an exceptional ability to sweat. Humans possess more sweat glands than any other animal, making perspiration a critical adaptation for savanna life.

4. Lastly, hairlessness may have helped them avoid lice, fleas, and other parasites that plagued their hairy primate relatives.

According to Harvard professor Richard Wrangham (2009), Homo erectus used fire to cook food, keep warm at night, and ward off predators. This could partly explain their hairlessness and their more efficient and smaller digestive system compared to their ancestors. Even if they were not yet cooking food with fire, they were certainly already using external methods such as grinding, grating, chopping, pounding, and mashing their food with tools. Wrangham refers to Homo erectus as ”the cooking ape.”

Homo erectus was also the first of our ancestors to regularly eat meat. While it is uncertain how they acquired it, all evidence suggests they were either hunters or systematic scavengers. Even today, African hunter-gatherers observe the movements of vultures to locate their next meal (Liebenberg 2013). When vultures fly in a group toward a particular direction, they are heading for a carcass. If they are circling over a specific spot, the kill has already been found. In such cases, it is a race against time—those who arrive first get the best parts. Lions, for instance, only eat their fill before abandoning a carcass, making it possible for bold and hungry scavengers to drive them away with loud noise. The fortunate ones are rewarded with nutrient-rich bone marrow and sometimes even meat. Hyenas, however, are much more efficient and faster scavengers, arriving at kills within 30 minutes and leaving nothing behind. This urgency may have played a role in shaping humans’ long-distance running abilities—only the fastest could reach a carcass before the hyenas.

Systematic scavenging is unpredictable since it depends on the hunting success of other predators. Even when a carcass is available, it requires an alert scavenger, who happen to be nearby. Yet, Homo erectus consumed meat regularly, leading many researchers to conclude that they were also active hunters. However, there is no surviving evidence of effective hunting weapons from their time. They crafted simple stone tools suited for cutting, slicing, and pounding, along with more refined tools that could function as knives or scrapers. It is likely they also created tools from biodegradable materials such as wood, bark, or grass, which have not survived to the present day.

Hunting without weapons

The question is: if Homo erectus lacked sophisticated hunting weapons, how did they obtain meat?

Nearly all significant differences between Homo erectus and modern chimpanzees relate to locomotion. While chimpanzees still spend most of their time climbing trees, with long arms, short legs, and prehensile toes suited for an arboreal lifestyle, Homo erectus had traded these adaptations for something else entirely.

David Carrier (1984), Dennis Bramble (Bramble & Carrier, 1983), and my friend and supporter, Harvard professor Daniel E. Lieberman (2013), have proposed that Homo erectus was an endurance runner, shaped by natural selection for persistence hunting. This hypothesis explains many of their unique physical traits, particularly those related to energy efficiency, skeletal structure, balance, and thermoregulation. Unlike other apes, human feet generate force with minimal energy expenditure. The Achilles tendon, crucial for running, is disproportionately large in humans and first appears in Homo erectus. Their foot arch and larger joint surfaces resemble those of modern humans, suggesting greater endurance and stress tolerance. Additionally, larger gluteal muscles and the nuchal ligament (which stabilises the head) allowed for better balance. Without the nuchal ligament, a runners head would wobble uncontrollably—similar to how a pig’s head bobs when it runs.

Homo erectus also had a leaner body optimised for heat dissipation, with sweating and hairlessness playing major roles in preventing overheating. More efficient cerebral blood circulation helped cool the brain while running under the African sun.

Lieberman and his colleagues have demonstrated that, given the right conditions, humans can outrun nearly any animal over long distances. Persistence hunting involves selecting a large, easily exhausted prey—such as an antelope or a giraffe—and chasing it at a steady pace. Quadrupedal animals must synchronise their breathing with their stride because their internal organs bounce with each step. This means they must periodically stop to pant and cool down. In contrast, a bipedal runner like Homo erectus could breathe independently of their stride. Moreover, furry quadrupeds expose much of their body to the sun, accelerating heat buildup. For Homo erectus, only the scalp and shoulders were directly exposed to sunlight.

As recently as the 1990s, some hunter-gatherer groups in Botswana still practiced persistence hunting, proving it to be an effective way to secure large amounts of meat. Only when big game became scarce did humans abandon this ancient method, which had once made all of us endurance runners.

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Resources:

Bramble, D. M., & Carrier, D. R. (1983). Running and breathing in mammals. Science, 219, 251–256.

Carrier, D. R. (1984). The energetic paradox of human running and hominid evolution. Current Anthropology, 25, 483–495.

Ijäs, M. R. (2020). Fragments of the hunt: Persistence hunting approach to rock art. Hunter Gatherer Research, 6(3–4).

Ijäs, M. (2017). Fragments of the Hunt: Persistence Hunting, Tracking and Prehistoric Art. Helsinki: Aalto University.

Liebenberg, L. (2013). The origin of science. Cape Town: CyberTracker.

Lieberman, D. E. (2013). The Story of the Human Body: Evolution, Health, and Disease. New York: Pantheon Books.

Wrangham, R. (2009). Catching Fire: How Cooking Made Us Human. London: Profile Books.