Time and time again the standard account of human evolution turns out to be incorrect. With this latest insight, evolutionary biologists are left without an explanation for the origin of the remarkable manual dexterity of humans and the genesis of tool usage. It seemingly was capable of doing so all along. Perhaps even more significant is the recognition that the human hand didn’t evolve over time to be better adapted for tool use. In fact, it’s not clear what this creature looked like. That is, the evolutionary ancestor of humans wasn’t a knuckle-walking ape-like creature at all. Even though the standard evolutionary model regards the last common ancestor of humans and chimps as chimp-like, this latest study indicates that this view is incorrect. This work has far-reaching implications when humanity’s origin is viewed from an evolutionary vantage point. On the other hand (no pun intended), chimps and orangutans display similar hand proportions, reflecting convergent evolution. The evolutionary tree they built indicated that human and gorilla hands are very similar, suggesting an ancestral state. They discovered that the hand proportions of monkeys and apes are quite diverse, and the human hand isn’t necessarily that unique. These researchers reached this conclusion after doing a careful comparison of human hand proportions with those of monkeys, apes, and the fossil remains of early hominid species and by using this hand data to build an evolutionary tree. In other words, the human hand is primitive and the chimpanzee hand represents an evolutionarily advanced state. 1 Researchers from George Washington and Stony Brook universities recently presented data that suggests that the last common ancestor of humans and chimps possessed a human-like hand, not a chimp-like hand. New work, however, undermines this standard evolutionary story. Presumably, strong selective pressure influenced the thumb and finger proportions (along with it the dexterity of the hand) as hominids began to use tools. While long fingers and a short thumb are ideal for knuckle walking, they have limited utility for tool making. They believe a knuckle-walking ape-like creature evolved the capacity for bipedalism, freeing the hands, which in turn evolved to become more dexterous. In spite of the human hand’s elegant design, many evolutionary biologists believe that it was shaped by an evolutionary history. In contrast, chimpanzees have much shorter thumbs, strikingly disproportionate to their long fingers. One of the unique features of the human hand is our lengthy thumbs. It permits humans to manufacture and use a wide range of tools, distinguishing us from animals and undoubtedly contributing to our success as a species. What's more, these asymmetries mirror those found in motor areas of humans, which suggests a common evolutionary origin, Hopkins says.The human hand is remarkable. 6) that corresponded with their handedness. These chimps had somewhat lateralized brains ( Behavioral Neuroscience, Vol. When Hopkins looked at MRI scans of these chimps' brains, he found that there were asymmetries between the hemispheres, especially in two motor cortex areas, the precentral gyrus and the inferior frontal gyrus. It turned out that chimps were extremely right-handed for this behavior ( Journal of Comparative Psychology, Vol. So he and his colleagues introduced themselves to a variety of chimpanzees and recorded which hand each chimp used to throw feces at them. "Chimps usually throw at new people-they'll often throw their at them," Hopkins explains. In 2004, he designed an experiment to determine which hand chimps throw with. In 1998, Hopkins and his colleagues established that when making one-handed gestures, like pointing to something, chimps almost exclusively use their right hands. A series of experiments in the '90s by Hopkins and others showed that movements requiring skilled coordination-the original research had chimps fishing peanut butter out of the end of a plastic pipe-were often done using the right hand, while the chimps were less preferential for unskilled movements such as simple reaching. But in the last decade, researchers have shown that other animals' brain hemispheres may be specialized for particular tasks.īill Hopkins, PhD, an Agnes Scott College primate researcher and biopsychologist, was one of the first to establish that, like humans, chimps tend to be right-handed, though not quite as ubiquitously as humans-about 70 percent. Historically, humans were the only animals thought to have handedness.
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