Why do we run

With running having such a drastic impact on our bodies both short and long term, is it something we're particularly well suited to do? Georgia Mills spoke with Daniel Lieberman is a professor at Harvard University of human evolutionary biology. He looks at when, why and how humans first got on the fast-track...

Daniel - Well humans have probably been running...always right? You know, our ancestors had to run away from leopards and predators or when they fight each other. But we started probably to do long distance running, a very peculiar form of running, sometime between about two and three million years ago.

Georgia - Why do you say long distance is a peculiar form of running?

Daniel - Well very few animals run long distances. So chimpanzees for example, or other monkeys and apes, will run occasionally, but usually they sprint briefly for 100 meters or so and then they collapse. They get hot and bothered and they don't really go very far, just to get away from each other when they're fighting or to get away from a predator that chases them briefly into a tree. But humans are special. Humans are one of a few groups of animals that will run very long distances, like five or ten or fifteen kilometers on a regular basis. Not many animals do that.

Georgia - And why did we start doing that.

Daniel - Well it's impossible to know for sure without a time machine. But the only explanation that anybody's really been able to come up with is that we ran in order to get meat. You know, carnivores have to run. Most carnivores do that by chasing rapidly their prey, they sprint, so think of a cheetah chasing a gazelle. But we can't do that. Humans are slow. Because we're bipeds we can produce force with only two legs as opposed to four legs. So we're about half as slow as most animals our body size.

And so humans do something completely different. We chase animals over long distances and tire them out. We actually cause them to develop heatstroke. Here's how it works. Most animals when they run, they use four legs and they cool by panting and it's not that effective a way of cooling your body. We cool by sweating, so we secrete water all over our bodies and that enables us to dump heat very effectively. And that gives us a huge advantage over four-legged animals because four-legged animals can pant when they're trotting but when four-legged animals run fast, when they gallop, they can no longer pant. And the reason for that is that galloping is a sort of seesaw gait in which the guts of the animal slam into the diaphragm with every step. So galloping animals, if you take a dog for a run you can find this out very quickly, if you make your dog run fast your dog will have to gallop. The dog will not be able to pant while it's galloping. Don't do this for too long on a hot day or you’ll kill your dog. But we can,  because we don't gallop, we don't have that problem.

So if you can make an animal gallop for a long period of time in the heat you can actually cause that animal to overheat and it will collapse. So hunters sometimes take advantage of this. What they'll do is they'll find an animal, and they'll find the biggest animal they can because big animals just like big humans overheat faster than small animals, and then they'll chase it. And of course the animal will run faster than the human can but the human will track it and then chase it again. And if the hunter can get to the animal and chase it again before the animal has cooled down, then the animal's body temperature will go up and up and up and up and eventually, usually after about a half marathon’s distance of running, the animal will completely collapse and then the hunter doesn't even need any weapons or technology, can just walk up and kill it with a rock or something like that without much danger.

Georgia - You put your money where your mouth is, is that right, in this theory?

Daniel - Oh yeah. So a few years ago, just to kind of try this out, I entered a race that's been run every year for the last, I don't know, 25 years or so, in a town called Prescott, Arizona. It's called Man Against Horse. And every year a bunch of humans race horses over a mountain. It's a marathon length race and even though I'm not a particularly great runner, I'm just a middle aged professor, there were I think fifty-something horses and I beat all but thirteen of them. And again, I am not a great runner, I'm not an elite runner. And the reason is the horses get too hot, but the humans can keep going.

Georgia - Considering then that this long distance running was basically how we got our food, what ways did our bodies change, how did we adapt to this lifestyle?

Daniel - Our bodies are changed literally from head to toe. I mean we have features all over our bodies that help us be incredible long distance runners and they include having short toes. So we have short toes to prevent ourselves from breaking them when we run. We have arches in our feet which act like springs, which store and release mechanical energy. We have long Achilles tendons, much, much longer than those of say chimpanzees and gorillas. And again those ac as giant springs to help us run efficiently. The largest muscle in our body is the gluteus maximus, that very beautiful muscle indeed but also very important for running and to prevent us from falling over and not important for walking. We have waists that are able to twist independently, we have special mechanisms in our necks to help keep our head stable, we're furless and have sweat glands all over our bodies. In our ears we have organs of balance that are specially tuned to handle the frequencies and demands of running. I mean literally we have changes from the tops to the bottoms of our body that make us really good at running...