Before they walked the walk, humans shuffled

BEIJING, May 30 (Xinhuanet) -- Before humans learned to walk the walk, they learned to shuffle, according to a mathematical model suggesting shuffling was a precursor to walking as a way to save metabolic energy between 4 million and 7 million years ago.

The theory behind the talk is some hungry primate was perhaps picking fruit, stood on its hind legs and reached up, and then rather than revert to a four-legged stance, shuffled over to another bit of low-hanging fruit.

"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 University of Washington assistant professor of anthropology and co-author of the new study.

"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 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.

"A chimp's body plan is very much like that of a primitive ape, and our last common ancestor probably had a body like that of a chimp," Kramer said. "Modern humans are different with long legs and a big head. So chimps are a good place to start."

Using the model they devised, Kramer and Sylvester calculated it would not be metabolically efficient for a chimp to use bipedalism for distances greater than about 50 feet. But it would be efficient for distances less than 30 feet, and that's when most shuffling would occur. In addition, walking on two feet would be used most frequently for distances less than three feet.

"These are predictions other people can test," Kramer said. "You should rarely, if ever, see a chimp walking upright at longer distances. The flip side of this is if a chimp is going a short distance returning to all fours is not going to happen. You can see this in human babies learning to walk. If they are going between a couch and a coffee table, they are up on their feet. But if they are going a longer distance, they go down and crawl."

(Agencies)