Evolution of the Long Distance Runner

 
Today's Toronto Star has a feature article on marathon running [Any schmo can run a marathon]. The subtitle is more informative "Humans, scientists say, are built for speed – or, at least, endurance. It's all in our shortish toes and big behind."

As one of those schmos who can't run a marathon,¹ I'm always intrigued by claims that all the rest of you have evolved over millions of years to become the perfect marathon runners. The article, by staff reporter Cathel Kelley, focuses on the claims of Daniel Lieberman, an anthropologist at Harvard University. He is one of many scientist who claim that humans are vastly superior at long distance running compared to other mammals, and even compared to our ancestors. They claim there's been selection for the ability to run long distances. Is this a reasonable explanation?

Lieberman's latest paper shows that individuals with short toes are possibly better runners than those with longer toes (Rolian et al. 2009). Since humans tend to have shorter toes than non-bipedal primates, this suggests a possible evolutionary adaptation to running.

An earlier paper promoted the idea that our gluteus maximus (GM) muscle is also an adaptation for long distance running (Lieberman et al. 2006). The closing paragraph of that second paper supports an adaptive explanation but it expresses the appropriate caveats.

Future experimental and paleontological research is necessary to clarify the functional and evolutionary history of the human GM. Based on the above results, we offer several alternative scenarios that merit further study. As noted above, one possibility is that australopithecines had an intermediate configuration of the GM (Berge, 1994Go; Berge and Daynes, 2001Go), retaining some kind of caudal portion but with a less expanded cranial portion than is evident in Homo. If so, then the caudal portion would likely have been an effective extensor of the femur during climbing and perhaps walking, and the cranial portion would have helped to stabilize the sacrum, but probably would not have been a strong trunk stabilizer. An implication of this scenario is that the expansion of the cranial portion of the GM is a derived trait of Homo that would have been selected for control of trunk flexion during endurance running (Bramble and Lieberman, 2004Go) and/or foraging (Marzke et al., 1988Go). An alternative possibility, however, is that the configuration of the GM in Australopithecus was much like that of Homo in terms of the loss of the GMIF. Either the australopithecine GM as a whole was relatively smaller, as many researchers suggest, or possibly as large as in humans (Haeusler, 2002Go). As shown above, the GM in either case is unlikely to have played much of a role in level terrain walking, and is unlikely to have been selected for running given that the genus lacks many other features associated with running capabilities (Bramble and Lieberman, 2004Go). According to this scenario, the derived anatomy of the GM in Australopithecus was probably a reconfiguration of the gluteal musculature for climbing, or a novel adaptation for foraging tasks such as digging that involve flexion of the trunk (Marzke et al., 1988Go). We cannot discount the hypothesis that expansion of the GM might have been useful for walking on uneven terrain. However, it is clear that expansion of the GM in Homo would have benefited any activity that requires trunk stabilization, especially running. Regardless of which scenario is correct, the expansion of cranial portion of the GM is a uniquely hominid characteristic, perhaps distinctive to the genus Homo, which played a vital role in the evolution of human running capabilities.

The newspaper description of the endurance running hypothesis (ERH) is a little more descriptive.

Humans' ability to run is unique among primates.

Why running? Because that's how we killed our food.

Experts call it persistence hunting. The Homo genus did not develop the most basic projectile – the spear – until 200,000-300,000 years ago. That left our ancestors equipped with little more than sharpened sticks for nearly two million years of carnivorous prehistory.

"Even middle-aged college professors can run at a speed that's above the trot-gallop transition of most animals," Lieberman says.

"Why is that important? Quadrupeds cannot pant and gallop at the same time. Their guts are too busy sloshing around like a piston. So, every 10 or 15 minutes, they overheat."

When they overheat, animals must stop to cool. But their bipedal pursuers keep on coming. After several stops and starts, the prey succumbs to heat exhaustion or its heart gives out.

This explains why they don't run the Iditarod in August.

Lieberman contends that this is the only explanation of how humans were capable of killing large game before developing projectile weapons.

"I defy most people to go out and kill a wildebeest with a wooden stick," he says.

Here's how I understand this story.

About one million years ago the entire human population was engaged in hunter-gatherer activities on the African savanna. Most of the small groups obtained a significant amount of their food by hunting large animals. The males would run after these large animals with no weapons. The animals would run away but the humans kept chasing them until the animals couldn't run any more and they dropped dead. (Presumably the wildebeests never caught on to the fact that they could just turn around and gore the pesky humans. Or maybe they couldn't because the humans could outrun them? Here's what happens when marathon-adapted humans try running with bulls.)

There was considerable variation within the human population. Some men had short toes and some men had long toes. Some men had well-developed gluteus maximus muscles and some men didn't. Presumably, the men with genetic traits that enabled them to run faster or farther than the other men got more food than their friends. Their friends either died of starvation or else they had so little meat they couldn't get a mate and reproduce.

Over time there was selection for men who could run farther and faster and humans became adapted to long-distance running. (Presumably the women were good at it as well because they inherited their genes from their fathers.)

When humans began to inhabit other locations that didn't require running, the adaptations remained because by that time all the low fitness variations had been eliminated from the population. That's why there was no loss of this ability when humans began to settle in northern forests and caves, and began to farm and create cities. We all remain well-adapted to long distance running so that, with only a little training, we could all chase down a wildebeest on the African savanna.

I assume the wildebeests just didn't evolve as quickly or they would have adapted as well.

The bison on the North American plains probably could run faster than the natives because, to the best of my knowledge, the North American natives didn't run after buffalo in order to make them die of heat exhaustion. They used sneaky tricks like forcing them to charge over cliffs. They also sneakily used bows and arrows. The natives only started chasing buffalo when horses became available, which is very strange since humans are better at long-distance running than horses—or so the story goes.

One of the problems with evolutionary psychology is that the psychologists claim to know exactly what human societies were like one million years ago. That's one of the problems with the endurance running hypothesis as well. It is based on the assumption that we know how primitive societies obtained food (by running after large animals on the savanna). In fact, we don't know if this is true and we don't even know what percentage of the species might have adopted this lifestyle.

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1. Because my toes are too long.

[Image Credit (upper): Constantina Dita-Tomescu]

Lieberman, D.E., Raichlen, D.A., Pontzer, H., Bramble, D.M., and Cutright-Smith, E. (2006) The human gluteus maximus and its role in running. Journal of Experimental Biology 209:2143-2155. [DOI: 10.1242/jeb.02255]

Rolian, C., Lieberman, D.E., Hamil, J., Scott, J.W., and Werbel, W. (2009) Walking, running and the evolution of short toes in humans. Journal of Experimental Biology 212:713-72. [DOI: 10.1242/jeb.019885]