More on Brains vs Brawn in Human Evolution

After considering the failure of genetic analysis to confirm the trade-off of brain vs. brawn, I checked what the evidence is that the chimps are so much stronger than humans. The answer is: they are not. The difference in strength is on the order of 1.5 times greater for chimps, not 3 to 5 times. Chimps do have a different mix of muscle fiber types than humans: a greater proportion of fast-twitch fibers, suited to rapid movement, than humans, who have more slow-twitch fibers, suited for endurance. The trade-off might be between two different ways of moving. This fits in with evidence on the hunting strategies of chimpanzees compared with those of modern-day bushmen. To see this, it is necessary to go back to the most fundamental distinction between hominins and the rest of the great Apes of Africa.

haina-kalahari-lodge-bush-men-hunting-zebra-590x390
Bushmen hunting – Siyabona Africa, African Safari Lodges

A major difference between chimpanzees and the earliest hominins was bipedalism. Chimps can stand on two feet and walk short distances bipedally. But they rarely do that, usually walking or running on their knuckles and the soles of their feet. Ardipithecus could move bipedally as well as climb trees (~ 4.4 million years ago), and this was a habit with Australopithecines ~ 3.5 to 2 million years ago. The suggestion is that upright walking was related to a major difference in the lifestyle and habitat of the hominin vs the chimpanzee lineage. Present-day chimpanzees live deep in the forests of Africa. They eat fruits and nuts, insects, and the occasional monkey that they (very cleverly) hunt by teamwork (click here for a video of a band of chimps hunting). Some present-day human hunter-gatherers live in forests also, but others live in more open country, unlike chimpanzees. Bushmen living on the savannah practice persistence hunting. Teams of bushmen in the open can move for long periods of time and wear down the resistance of prey animals such as kudu. They provoke panic in a herd, then work on isolating a male, so that his tracks are not obscured by those of other members of the herd. Often the team then delegates one member to continue the long-term chase of the male. The male runs as long as it can, then hides in the bush in order to rest, but the man is good at tracking, forcing it to flee again. After many hours of this, the hunter arrives before the animal can recover the ability to run, thus enabling the man to finish it off with a spear, and return to camp to get help carrying the kill back to camp. Click here for a video from David Attenborough’s documentary of this hunting strategy.

Homo erectus and its successors were omnivorous, but we do not know for sure whether they hunted like contemporary bushmen. There is some evidence that they learned to use fire by about 600,000 years ago, perhaps earlier. But all the hominins, including the Australopithecines, were bipedal, probably living in different places than those currently occupied by chimpanzees, and probably using their arms and hands to carry food and babies. With the development of tools and the control of fire for cooking and other purposes, they most likely became even more efficient hunters and scavengers on the plains. Thus they were embarked on a different path from their cousins, the ancestors of today’s chimpanzees. We can see several ways in which the body and mind of man were adapted to this different lifestyle, for example hairlessness, which enables the man to sweat and cool off during the chase, and the ability to carry water along, to replenish what he has lost through his effort. The chimpanzee’s way of hunting is very different, depending on speed, numbers of pursuers, and an ability to climb and descend rapidly in the forest. It seems that the differences in their muscle tissue make sense in the light of their respective hunting strategies. The trade off of fast vs slow twitch muscle fibers is a good candidate hypothesis for establishing the two lineages, along with the difference in habitat.

Long term, hominins developed vastly different behaviors from the chimpanzees. These behaviors were largely cultural, but they arose from bipedalism at first and later, in an accelerating manner, the manufacture of tools. Homo sapiens and Homo neanderthalensis wound up with brains twice the size of Homo erectus’. This change took place with little or no increase in physical stature: after Homo erectus, hominins succeeded without getting taller. Recent work has clarified our relationship with other species of hominins, especially the Neanderthals.

Neanderthals had an identical hyoid bone to ours. Both are very different from that of chimpanzees. The hyoid in humans is part of the vocal apparatus. Experiments with physical models show that the chimpanzee hyoid obscures the clarity of spoken words, while ours and presumably the Neanderthal’s were better adapted to the production of comprehensible speech. The FoxP2 gene in humans, in mutant form, causes a profound language deficit, showing that this gene is an important part of the development of the vocal apparatus. The FoxP2 gene in Neanderthals is identical to that in Homo sapiens, each being two amino acids different from that of chimpanzees. This and other evidence suggests that the Neanderthals used language. So it is possible that language evolved about half a million years ago, at or before the time of our common ancestor with the Neanderthals. Recent evidence shows that Homo sapiens was present in Africa about 300,000 years ago. The skull of these early specimens is elongated, but comparable in size to modern humans. This size was matched and even exceeded by that of the Neanderthals. So it is possible that modern brain size was achieved by half a million years ago in the common ancestor of Neanderthals and Homo sapiens. Alternately, it was somewhat less at first, and increased independently in the two species in the ensuing 200,000 years. After that, however, it stopped increasing. Neanderthals and early Homo sapiens practiced burial and decoration of their bodies using beads, and even made flutes. Homo sapiens, but not Neanderthals, show signs of great cultural sophistication starting about 50,000 years ago, with the independent production of rock art in Australia, Indonesia, and Europe.

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Aurochs, horses, deer – Lascaux (from Wikipedia)

This suggests that the human brain was developed to a point that permitted, but did not necessarily dictate, a cultural breakthrough that arguably put our intellect leagues beyond all the apes, past and present. But that was not the end of the game.

For most of our history, human populations  were low.  About six thousand years ago, again in several places scattered across the globe, Homo sapiens invented agriculture. Agriculture freed up time and permitted the division of labor that would lead to the construction of cities, and the invention of writing. After that our history has been written down to various degrees of fidelity. It is only after the development of science and powered industry that we began to develop the very great populations of today. But even that was not the end of the game. Our culture, aided by science, has now put us in a position to alter the very genes that we carry, or to exterminate ourselves in a nuclear holocaust. Many choices with momentous consequences lie before us.

As for the brains vs brawn theory, we see that it is probably a gross oversimplification. It is simply restating facts to point out that humans are weaker, but smarter than chimps. The details are far more interesting and nuanced.

Additional Reading

Tattersall, I (2004) What happened in the origin of human consciousness?The Anatomical Record 276B, January 2004 pp 19–26.

MICHAEL GRAZIANO A New Theory Explains How Consciousness Evolved
A neuroscientist on how we came to be aware of ourselves.
Chris Helgren / Reuters Atlantic Monthly JUN 6, 2016

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