The secret to chimp strength
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. 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. Indeed, biologists have uncovered differences in muscle architecture between chimpanzees and humans. But evolutionary biologist Alan Walker, a professor at Penn State University, thinks muscles may only be part of the story. 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. Our fine motor control prevents great feats of strength, but allows us to perform delicate and uniquely human tasks.
Walker's hypothesis stems partly from a finding by primatologist Ann MacLarnon. MacLarnon showed that, relative to body mass, chimps have much less grey matter in their spinal cords than humans have. Spinal grey matter contains large numbers of motor neurons—nerves cells that connect to muscle fibers and regulate muscle movement.
More grey matter in humans means more motor neurons, Walker proposes. And having more motor neurons means more muscle control.
Our surplus motor neurons allow us to engage smaller portions of our muscles at any given time. We can engage just a few muscle fibers for delicate tasks like threading a needle, and progressively more for tasks that require more force. Conversely, since chimps have fewer motor neurons, each neuron triggers a higher number of muscle fibers. So using a muscle becomes more of an all-or-nothing proposition for chimps. As a result, chimps often end up using more muscle than they need.
"[A]nd that is the reason apes seem so strong relative to humans," Walker writes.
Our finely-tuned motor system makes a wide variety of human tasks possible. Without it we couldn't manipulate small objects, make complex tools or throw accurately. And because we can conserve energy by using muscle gradually, we have more physical endurance—making us great distance runners.
Great apes, with their all-or-nothing muscle usage, are explosive sprinters, climbers and fighters, but not nearly as good at complex motor tasks. In other words, chimps make lousy guests in china shops.
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. 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.
"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. "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."
Walker says that testing his hypothesis that humans have more motor neurons would be fairly straightforward. However, he concedes that testing whether humans have increased muscle inhibition could be a bit more problematic.
- The secret to chimp strengthfrom Science CentricTue, 31 Mar 2009, 9:21:07 EDT
- The secret to chimp strengthfrom Science BlogMon, 30 Mar 2009, 22:14:16 EDT
- The secret to chimp strengthfrom Biology News NetMon, 30 Mar 2009, 21:28:34 EDT
- The secret to chimp strengthfrom Science BlogMon, 30 Mar 2009, 18:49:10 EDT
- The secret to chimp strengthfrom PhysorgMon, 30 Mar 2009, 17:49:21 EDT
Latest Science NewsletterGet the latest and most popular science news articles of the week in your Inbox! It's free!
Learn more about
Check out our next project, Biology.Net
From other science news sites
Popular science news articles
- 'Adaptive protein crystal' could form new kind of protective material
- ALMA measures mass of black hole with extreme precision
- Measuring a black hole 660 million times as massive as our sun
- Six new fossil species form 'snapshot' of primates stressed by ancient climate change
- 'Slow' NZ seabed quake sheds light on tsunami-earthquake mechanism
- Algae use their 'tails' to gallop and trot like quadrupeds
- Study suggests medical errors now third leading cause of death in the US
- Stickleback fish adapt their vision in the blink of an eye
- Perceived diversity in neighborhoods is related to more prejudice, study finds
- Imodium for a legal high is as dumb and dangerous as it sounds
- Ancient marine sediments provide clues to future climate change
- It takes more than peer pressure to make large microgels fit in
- Hubble discovers moon orbiting the dwarf planet Makemake
- Hybrid forms of the common house mosquito may serve as vectors between birds and humans
- Fossils may reveal 20-million-year history of penguins in Australia