With the civilizational bias that skews most people’s perceptions of human history, we have come to regard the notion of ‘primitive’ through its connotations, crude, unsophisticated, and poorly developed. Yet what is primitive is primary. It is the origin from which we have strayed and the essential we have largely forgotten.

Daniel Lieberman: [I]ncreases in brain size were not really an early event in human evolution, and in fact, they didn’t occur until after hunting and after the invention of hunting and gathering, and not even until cooking and various other technological inventions, which gave us the energy necessary to have really large brains.

Brains are very costly. Right now, just sitting here, my brain (even though I’m not doing much other than talking) is consuming about 20- 25 percent of my resting metabolic rate. That’s an enormous amount of energy, and to pay for that, I need to eat quite a lot of calories a day, maybe about 600 calories a day, which back in the Paleolithic was quite a difficult amount of energy to acquire. So having a brain of 1,400 cubic centimeters, about the size of my brain, is a fairly recent event and very costly.

The idea then is at what point did our brains become so important that we got the idea that brain size and intelligence really mattered more than our bodies? I contend that the answer was never, and certainly not until the Industrial Revolution.

Why did brains get so big? There are a number of obvious reasons. One of them, of course, is for culture and for cooperation and language and various other means by which we can interact with each other, and certainly those are enormous advantages. If you think about other early humans like Neanderthals, their brains are as large or even larger than the typical brain size of human beings today. Surely those brains are so costly that there would have had to be a strong benefit to outweigh the costs. So cognition and intelligence and language and all of those important tasks that we do must have been very important.

We mustn’t forget that those individuals were also hunter-gatherers. They worked extremely hard every day to get a living. A typical hunter-gatherer has to walk between nine and 15 kilometers a day. A typical female might walk 9 kilometers a day, a typical male hunter-gatherer might walk 15 kilometers a day, and that’s every single day. That’s day-in, day-out, there’s no weekend, there’s no retirement, and you do that for your whole life. It’s about the distance if you walk from Washington, DC to LA every year. That’s how much walking hunter-gatherers did every single year.

In addition, they’re constantly digging, they’re climbing trees, and they’re using their bodies intensely. I would argue that cognition was an extremely important factor in human evolution, along with language, theory of mind — all those cognitive developments that make us so sophisticated. But they weren’t a triumph of cognition over brute force; it was a combination. It was not brains over brawn, it was brains plus brawn, and that made possible the hunter-gatherer way of life.

What hunter-gatherers really do is they use division of labor, they have intense cooperation, they have intense social interactions, and they have group memory. All of those behaviors enable hunter-gatherers to interact in ways such that they can increase the rate at which they can acquire energy and have offspring at a higher rate than chimpanzees. It’s a very energetically intensive way of life that’s made possible by a combination of extraordinary intelligence, inventiveness, creativity, language, but also daily physical exercise.

The other reason we often discount the importance of brawn in our lives is that we have a very strange idea of what constitutes athleticism. Think about the events that we care about most in the Olympics. They’re the power sports. They’re the 100-meter dash, the 100-meter freestyle events. Most athletes, the ones we really value the most, are physically very powerful. But if you think about it this way, most humans are wimps.

Usain Bolt, who is the world’s fastest human being today, can run about 10.4 meters a second, and he can do so for about ten or 20 seconds. My dog, any goat, any sheep I can study in my lab, can run about twice as fast as Usain Bolt without any training, without any practice, any special technology, any drugs or whatever. Humans, the very fastest human beings, are incredibly slow compared to most mammals. Not only in terms of brute speed, but also in terms of how long they can go at a given speed. Usain Bolt can go 10.4 meters a second for about ten to 20 seconds. My dog or a goat or a lion or a gazelle or some antelope in Africa can run 20 meters a second for about four minutes. So there’s no way Usain Bolt could ever outrun any lion or for that matter run down any animal.

A typical chimpanzee is between about two and five times more powerful than a human being. A chimpanzee, who weighs less than a human, can just rip somebody’s arm off or rip their face off (as recently happened in Connecticut). It’s not that the chimpanzee is remarkably strong, it’s that we are remarkably weak. We have this notion that humans are terrible natural athletes. But we’ve been looking at the wrong kind of athleticism. What we’re really good at is not power, what we’re really phenomenal at is endurance. We’re the tortoises of the animal world, not the hares of the animal world. Humans can actually outrun most animals over very, very long distances.

David Attenborough follows the San people of the Kalahari desert, the last tribe on earth to use persistence hunting.