![]() The results, the researchers speculate, suggest that our reliance on recognising faces to know who’s who could have evolved from an earlier reliance on buttocks. The so-called inversion effect means that humans process information about faces in a totally different way to how they process information about other objects. While the importance of buttocks in chimpanzee society is well-known – the anogenital region of chimpanzee buttocks swells and reddens around the time of ovulation, for example – it wasn’t known if they processed characteristics of individual buttocks in the same way as humans process faces. The image in the top-right shows distinguishing features of chimpanzee buttocks (left) and human faces (right) Mariska E. Future research may probe when human ancestors switched from in-synch to out-of-synch movements of the hips and trunk, and why evolution favored that path for our upright locomotion.A chimpanzee is asked to match upright and inverted images of faces, buttocks and feet. Two-legged running, however, which requires larger cancellations between movement of the hips and trunk, “may have been somewhat less effective,” the team writes. “These results show that chimpanzees utilize rotations to counter pelvic rotations in much the same was as humans,” the authors write.Īs they report this week in Nature Communications, these findings disprove the assumption that chimps are completely rigid up top, and they have interesting implications for the evolution of bipedal walking in humans.Įven if early chimp-like hominins had chimp-like pelvises that rotated up to 50 percent more than those of modern humans, they could probably still walk upright and save energy by swinging their trunks in time with their hips. The team found only a 0.4 -degree difference in axial rotation between the human and chimp trunks. ![]() The chimps’ sway does work to conserve some energy, and the degree to which their rib cages move is almost the same as that of humans. Humans, meanwhile, move those structures in the opposite direction. This allowed the team to compare how our two related species move, and also to break down each style of walking into its specific parts.Ĭontrary to common assumptions, they found that the chimps' upper bodies do twist slightly as they walk but their ribs and hips move in the same direction. The scientists attached motion-measuring markers on numerous points on the chimps as well as on human volunteers, and then measured the paths those markers took as their wearers walked forward. Hercules and Leo, two chimps trained to walk upright, helped the researchers arrive at these findings. That suggests our chimp-like human ancestors, such as Australopithecus afarensis, might have been some of the first hominins to stand on their own two feet. Using kinematic analysis, a team of researchers from Stony Brook University and the University of Arizona College of Medicine found that chimp and human locomotion share more similarities than previously thought. Until now, however, no one ever verified that assumption. Following this logic, scientists also concluded that human ancestors prior to Homo erectus-whose morphology shares commonalities with chimps-likely walked that way, too. ![]() ![]() Pairing that observation with studies of chimp bone structure, researchers had long assumed that our closest relatives lack the counter-rotations characteristic of human motion. As they make their way forward, the trunk appears rigid while the swing of the hips and arms seems overly pronounced and somewhat clumsy. When they do walk upright, their compact trunks and tall, wide hips cause them to stoop. Finally, swinging arms counterbalance the sway of the hips, completing the characteristic human gait.Ĭhimpanzees, on the other hand, can be trained to walk on two hind legs and will occasionally do it in the wild, but it is not their preferred means of getting around. As the pelvis rotates forward, the trunk moves in the opposite direction, cancelling out angular momentum and reducing the amount of energy burned while walking. When we humans strut our stuff, we do it by coordinating the movements of our hips and upper bodies. ![]()
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