A research team which has been investigating similarities and differences between humans and our closest relative, chimpanzees, have found that the chimps rotate their torsos when they walk, just as much as we do. That means scientists will have to toss out previous assumptions about chimps and early humans alike, both of whom were thought to have rigid trunks suited for tree climbing.

The scientists had made this assumption based on similarities between the skeletons of chimpanzees and Australopithecus, one of our human ancestors. The most famous Australopithecus skeleton is nicknamed "Lucy" by English speakers.

If these new conclusions are correct, early humans were much more equipped to walk upright than previously thought. And they swayed their torsos like a veritable Marilyn Monroe—or at least like the rest of us. In fact, the researchers say the main difference between our torso motion and a chimp's is that the chimps swing their hips more, making them the sexiest primate after Martin Freeman.

Since Lucy and her pals have the same trunk structure as chimpanzees, we can assume they were rotating their torsos at about the same rate, and sashaying around like a bunch of go-go dancers.

"For instance, depending on who you ask, the 3.2 million-year-old Lucy fossil either rotated her pelvis exactly like modern humans or up to 2.5 times more," said Nathan Thompson, lead author and a Ph.D. student in the Department of Anatomical Sciences at Stony Brook University, in a press release.

The researchers used incredibly fine-tuned cameras to study how humans and chimps actually use their torsos while walking, unconscious movements that are typically unseen by the naked eye. Then they studied those movements in-depth using 3D computer models, and visualized the different ways Lucy and her contemporaries might have moved, given the new information about their torso flexibility. In all their simulations, Lucy would have had an upper body roughly like a modern human's.

"As we get a better idea of how our closest living relatives move, we are able to learn much more about the isolated piles of early human bones that the fossil record leaves us," said Thompson. "Only then can we paint a complete picture of how we evolved into what we are today."

The paper is titled "Surprising trunk rotational capabilities in chimpanzees and implications for bipedal walking proficiency in early humans," and is published in the journal, Nature Communications.

Photo: Ryan Somma | Flickr