Usain Bolt, the Jamaican sprinter who shattered two world records last week, may now be the world's fastest human, but his accomplishments raise some intriguing questions about how he and other humans match up against the rest of the animal kingdom.

At top speed, Mr. Bolt hit about 30 miles per hour as he set his records (he averaged 23.5 mph over 100 meters). The cheetah, in contrast, can reach a top speed of 70 mph and maintain it for about 200-300 yards, long enough to cream Mr. Bolt. The pronghorn can run at about 65 mph...