Several distinctive human features appear to be essential for running - an observation that has convinced Lieberman that running had a profound influence on shaping the human body. We would be very different animals if our ancestors hadn't needed to run after their dinners.
Even without scientists to study them, marathoners tell us something about our evolution: They disprove the popular wisdom that the growth of the brain necessitated the degeneration of the human body. It's true that we're no match for gorillas or chimpanzees in a fight, but when it comes to distance running, we kick the flat butts of all other primates and most other animals.
Dogs, cats, and many other animals can easily outsprint the fastest humans. But as the distances get longer, we start to catch up. No other primate can come close. As we branched off from other apes, "we've evolved all these metabolic mechanisms and thermoregulatory features," he said.
Lieberman had been studying the evolution of the human head, but was nudged toward the study of running by a pig.
The pig was on a treadmill for some other study when a colleague, Dennis Bramble, who was on sabbatical from the University of Utah, pointed out that the pig's head was bobbing all over the place. The researchers realized that pigs lacked what's called a nuchal ligament, which runs up and down the neck and helps some other animals keep their heads stable. Dogs and other good runners have a nuchal ligament and their heads don't bob around when they run.
Other apes don't have a nuchal ligament and we humans do, suggesting that it evolved independently in humans. Lieberman and Bramble soon found that the presence of a nuchal ligament leaves a distinctive mark on skulls, which led them to conclude that our ancestors got them about 2 million years ago.
