This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: New research suggests that no matter what we eventually determine the last common ancestor of humans and chimpanzees to be, we'll learn it was a primate that climbed trees. Humans and chimpanzees began their separate evolutionary paths 6 million to 7 million years ago, when they split from the last common ancestor (LCA) they shared.
Debate about the LCA hinges in part on the tree-dwelling environment from which humans emerged—whether it involved living among high horizontal branches, being able to reach them from the ground or, more likely, both. Chimpanzees have ankle flexion that makes them skilled tree-trunk climbers, but monkeys have been thought to navigate trees with their arms—which would influence what kind of ancestor researchers are looking for: one that climbed trunks or lived full time in treetops. Video evidence from West Africa suggests there may be no such distinction, at least based on foot structure.
Researchers from The Ohio State University observed and confirmed through measurements that wild sooty mangabey monkeys, known to have feet that lack chimps' versatile ankles, display foot-bone flexibility that facilitates vertical climbing up thin tree trunks to hide, forage or sleep. "People are making behavioral inferences from fossils, and some say a monkey can't vertically climb as well as an ape can," said first study author Luke Fannin, assistant professor of anthropology at Ohio State. "We're saying there's a functional equivalence here.
So you can't rule out vertical climbing just because something doesn't have a chimpanzee-like foot." The research appears this week in Proceedings of the National Academy of Sciences. Identifying the last common ancestor is considered key to helping us understand what led to bipedalism, which is habitual only in humans. We know we're apes, but this study makes the point that even if the ancestor had a more monkey-like foot morphology, it could still climb like an ape.
"Part of paleoanthropology is understanding how our evolution happened, and it's often through the hallmark of how we move because modern humans move quite differently than our cousins, the chimpanzees, do, and they're the living primates we're most closely related to," Fannin said. "And we're trying to understand why that is." Fannin recorded videos of mangabeys in the wild at the Taï Forest Monkey Project field station in Ivory Coast, co-directed by W. Scott McGraw, professor and chair of anthropology at Ohio State and senior author of the paper.
"The great thing about having the video is that it allows us to capture exactly what the monkey is doing in a high-resolution manner. So we can actually say how the joint is loaded. Before, we had hunches, but in this way, it's far more precise," McGraw said.
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