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It seems that mother nature has imposed a speed limit on how fast messages travel along nerves, and that may help explain why elephants have a lumbering gait, while mice are so fast on their feet.

Researchers at Simon Fraser University in British Columbia measured the nerve speed of a variety of mammals, ranging from elephants to shrews. They found that nerves of all the animals tested, regardless of size, conducted impulses at roughly the same speed - about 50 metres a second. That essentially means large animals are going to have a delayed reaction time compared with small creatures, because they have to transmit nerve data over much longer distances. (Think how hard it would be to catch mice in the wild with your bare hands. You may be big, but they're nimble.)

The senior author of the paper, Max Donelan, said it's theoretically possible for large animals to exceed the nerve speed limit - but they would require much thicker nerves. In order to have the same reaction time and sensory perception as a tiny shrew, the elephant would need, for example, a sciatic nerve with a diameter of 30 metres, said Dr. Donelan. Of course, that would be impractical.

But what they lack in speed and agility, bigger beasts tend to compensate with increased brain power. Indeed, Dr. Donelan, whose study was published in the Proceedings of the Royal Society B, thinks the nerve speed limit may have driven large animals to become smarter. "Large animals need to think ahead and predict any changes that will occur so they have time to adapt their movements according," he explained.

"It could be that the nervous systems of large animals evolved to become excellent predictive machines. A brain that is good at predicting movement may also become good at predicting other aspects of life," added Dr. Donelan, who believes such forces also had a role to play in the evolution of the human brain. After all, it takes a smart person to invent a better mouse trap.