How did humans get so smart?

It’s not all brains over brawn. Harvard professor Daniel Lieberman’s theory is that brawn has in fact been instrumental to the evolution of large brains.

The Human Evolutionary Biology professor boasts cult hero status in the running world and it is long-distance running that is central to his theory.

“In order for us to become very smart, we had to become endurance athletes,” he explained.

He turned the clock back two million years when our brains grew significantly larger than that of a chimpanzee and then about one million years when they grew to the approximate size they are today. Around five to seven million years ago there was a cooling of the Earth’s climate, he explained, which caused the rain forests to shrink. For those living on the margins, suddenly fruits were not so readily available and our ancestors had to travel farther to feed.

The first hominids were ape-like bipeds which allowed us to feed upright in the trees whereas chimps had to use four times as much energy getting around with their knuckles to the ground. But being on two feet made us unstable and less able to gather.

Some three million years ago the Earth cooled again causing an increase in the size of the grasslands. While the Australopiths grew giant teeth able to chew low quality food, the precursors of humans became high quality food specialists and invented hunting and gathering. They relied heavily on cooperation, food sharing and division of labour. They covered long distances every day and one of their high quality foods was meat.

Lieberman posed the question, “How did we hunt?” as the bow and arrow wasn’t invented until 100,000 years ago. “A sharpened stick or a club? It would have been easier to be a vegetarian,” he laughed.

“Me and my colleagues Dennis Bramble and David Carrier think the answer was our ability to run long distances.

“When you make a quadruped gallop, you limit how long that animal can run because galloping is not an endurance game. The reason for that is thermo regulation. Humans cool by sweating but animals cool mostly by panting and its tongue has a smaller surface area. When it gallops its guts start sloshing back and forth with every stride so as soon as they start galloping they have to synchronize every step with every breath and they cease the ability to be able to pant.

“We take advantage of our ability to do endurance persistence hunting and it is still practised today. Hunters will pick a big animal and make it gallop, get its core body temp up and up until it reaches a state of hyperthermia. At that point the hunter can easily walk up and dispatch it.”

It is at this part in our evolution that humans released the energetic constraints of their brains and that’s when brain size really started increasing.

“I hope I have convinced you that endurance exercise is an important part of our biological heritage. Endurance athleticism was a necessary precursor to us growing big brains that gave us culture and technology all the other things that make being a human so special. Exercise is good for us because it was what we evolved to do.”

TEDxBermuda 2011

• 'If the ocean's species die then we all die'
• Discovering the secrets of our tiger sharks
• A mural of epic proportions
• 'New wars are not breaking out in Africa, we are open for business'
• Spoken word artist Paynter receives a double standing ovation
• Music from around the world
• How did humans get so smart?
• Tales from within Guantanamo
• Taking from a society of waste and giving to a society of want
• Can our oceans heal themselves?
• Cleaning up corrupt professional cycling