![]() The Bastrop colony was supported by NIH/NCRR. MJB was supported by NICHD grant HD-38051, and NSF grants BCS-0634662 and SES 0729244. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.įunding: SFB was supported by NSF grant SES 0729244 and an NIH/NIGMS IRACDA grant awarded to Emory University. Received: NovemAccepted: DecemPublished: January 30, 2008Ĭopyright: © 2008 Brosnan et al. PLoS ONE 3(1):Īcademic Editor: Paul Zak, Claremont Graduate University, United States of America However, he concedes that testing whether humans have increased muscle inhibition could be a bit more problematic.Citation: Brosnan SF, Grady MF, Lambeth SP, Schapiro SJ, Beran MJ (2008) Chimpanzee Autarky. Walker says that testing his hypothesis that humans have more motor neurons would be fairly straightforward. "So there might be a degree of cerebral inhibition in people that prevents them from damaging their muscular system that is not present, or not present to the same degree, in great apes." "Add to this the effect of severe electric shock, where people are often thrown violently by their own extreme muscle contraction, and it is clear that we do not contract all our muscle fibers at once," Walker writes. Only under very rare circumstances are these limits bypassed-as in the anecdotal reports of people able to lift cars to free trapped crash victims. In addition to fine motor control, Walker suspects that humans also may have a neural limit to how much muscle we use at one time. In other words, chimps make lousy guests in china shops. Great apes, with their all-or-nothing muscle usage, are explosive sprinters, climbers and fighters, but not nearly as good at complex motor tasks. And because we can conserve energy by using muscle gradually, we have more physical endurance-making us great distance runners. Without it we couldn't manipulate small objects, make complex tools or throw accurately. Our finely-tuned motor system makes a wide variety of human tasks possible. "nd that is the reason apes seem so strong relative to humans," Walker writes. As a result, chimps often end up using more muscle than they need. So using a muscle becomes more of an all-or-nothing proposition for chimps. ![]() ![]() Conversely, since chimps have fewer motor neurons, each neuron triggers a higher number of muscle fibers. We can engage just a few muscle fibers for delicate tasks like threading a needle, and progressively more for tasks that require more force. Our surplus motor neurons allow us to engage smaller portions of our muscles at any given time. And having more motor neurons means more muscle control. More grey matter in humans means more motor neurons, Walker proposes. Spinal grey matter contains large numbers of motor neurons-nerves cells that connect to muscle fibers and regulate muscle movement. MacLarnon showed that, relative to body mass, chimps have much less grey matter in their spinal cords than humans have. Walker's hypothesis stems partly from a finding by primatologist Ann MacLarnon. Our fine motor control prevents great feats of strength, but allows us to perform delicate and uniquely human tasks. In an article to be published in the April issue of Current Anthropology, Walker argues that humans may lack the strength of chimps because our nervous systems exert more control over our muscles. ![]() But evolutionary biologist Alan Walker, a professor at Penn State University, thinks muscles may only be part of the story. Indeed, biologists have uncovered differences in muscle architecture between chimpanzees and humans. But what is it that makes our closest primate cousins so much stronger than we are? One possible explanation is that great apes simply have more powerful muscles. February's brutal chimpanzee attack, during which a pet chimp inflicted devastating injuries on a Connecticut woman, was a stark reminder that chimps are much stronger than humans-as much as four-times stronger, some researchers believe. ![]()
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