Rise of the planet of the humans

Anthropologist David Begun explains how our brains evolved by Patchen Barss

David Begun has been a
professor in the Department of Anthropology at U of T since 1989. He holds a PhD
in Paleoanthropology from the University of Pennsylvania. A frequent media commentator, he is currently editor of the Journal
of Human Evolution. His book, The Real Planet of
the Apes, will be published
by Princeton University
Press in 2013.

How did a weak-jawed, slow-moving, featherweight of a primate climb to the pinnacle of the food chain? How did these slightly-built bipeds turn their most deadly predators into prey? How did this frail species come to dominate desert, jungle and tundra — the harshest climates on the planet?

It’s all thanks to the 1.3 litres of neurons and chemicals that make up the human brain. Human intelligence was an evolutionary shift like no other, allowing us to overpower claws and fangs, withstand freeze and flood, and survive famine and disease.

A human being has a body mass similar to that of an antelope, but our brains are 10 times as large, and they use a fifth of our metabolic energy. We learn, solve problems, create and process information with unmatched speed and flexibility. Even our closest living relatives, bonobos and chimps, don’t come close.

Details are sketchy about the state of affairs three million (or so) years ago when our ancestors’ brains started to change. It appears, though, that the very products of human intelligence that make us so powerful — use of tools, complex social structures and language — were also the exact forces that created the modern brain.

“There’s feedback between technological change and developments in the brain,” says paleoanthropologist David Begun. “As technology develops, it becomes increasingly valuable as a support mechanism. Technology becomes the selective agent, rather than the environment.”

In other words, there was a shift in human evolutionary history after which a superior brain became more important to survival and reproduction than the ability to run, climb or throw a punch. Once natural selection started favoring those who could use a weapon, build a fire, tie a knot or forge an alliance, our evolutionary course was set.

“It wasn’t a punctuated event,” says Begun. “We see over time a gradual increase in brain size, both in absolute terms and relative to body size.”

Somewhere around two million years ago, though, came a turning point: intelligence went from being merely valuable to being essential. The species could no longer survive without technology.

Even as our brains were getting bigger and more complex, our jaws and biceps were receding.
“Once you lose the very powerful chewing apparatus, you are dependent on tools to process food,” Begun says.

The same goes for hunting and gathering, and for defense from predators and the elements. As our brains became more sophisticated, so did our language and culture. We developed spoken and written language, art, systems of government, music, science, philosophy, morality, religion, hobbies, humour and romance. Every new facet the human brain fed back into the evolutionary cycle, making this amazing organ that much more valuable to subsequent generations.

This process continues, and is, in fact, accelerating.

Every technological epoch — from the Stone Age to the Information Age, is superseded more quickly than the last. And at each stage, our brains become more central to survival.

Nobody knows if or when the human brain will reach the peak of its ascension. From ancient weapons to particle accelerators to the brain itself, we are still finding new ways to understand and exploit our world. One thing is certain: the journey isn’t over yet.