Did walking on 2 feet begin with a shuffle?

Somewhere in the murky past, between four and seven million years ago, a hungry common ancestor of today’s primates, including humans, did something novel. While temporarily standing on its rear feet to reach a piece of fruit, this protohominid spotted another juicy morsel in a nearby shrub and began shuffling toward it instead of dropping on all fours, crawling to the shrub and standing again.

A number of reasons have been proposed for the development of bipedal behavior, or walking on two feet, and now researchers from the University of Washington and Johns Hopkins University have developed a mathematical model that suggests shuffling emerged as a precursor to walking as a way of saving metabolic energy.

“Metabolic energy is produced by what an animal eats, enabling it to move. But it is a limited resource, particularly for young-bearing females which have to take care of and feed their offspring. Finding food is vitally important, and an animal needs to save energy and use it efficiently,” said Patricia Kramer, a UW research assistant professor of anthropology and co-author of a recent study.

She believes it was an empty belly, along with a need to conserve energy, that prompted that early ancestor to shuffle.

“Hunger. It is always hunger,” said Kramer. “There is nothing that will get you to do something you don’t want to do other than food. That’s why we bribe animals with food to train them.”

Because of a huge gap in the fossil record that hides when humans split off from other primates, Kramer and co-author Adam Sylvester, now a postdoctoral fellow at Johns Hopkins University, used the chimpanzee as a way of looking into the past and testing other researchers’ ideas about the origins of bipedalism.