STATE COLLEGE, Pa., April 1 (UPI) -- A U.S. evolutionary biologist says chimpanzees, which are several times stronger than humans, gain strength from their brains, as well as their muscles.
Although great apes are known to have more powerful muscles than humans, Pennsylvania State University Professor Alan Walker argues humans might lack the strength of chimps because human nervous systems exert more control over human muscles. That fine motor control, he said, prevents great feats of strength but allows the performance of delicate tasks.
Walker said his hypothesis stems partly from findings by primatologist Ann MacLarnon, who showed chimps have much less gray matter in their spinal cords than do humans. Spinal gray matter contains large numbers of motor neurons -- nerves cells that connect to muscle fibers and regulate muscle movement.
Walker said humans' surplus motor neurons allow the, to engage smaller portions of their muscles at any given time for delicate tasks, such as threading a needle, and progressively more for tasks that require 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, resulting in them using more muscle than they need.
Walker said that is the reason apes seem so strong relative to humans.
The study appears in the journal Current Anthropology.