No one knows whether Homo erectus, the early ancestor of both the Yankees and the Red Sox, threw the split-finger fastball.

But he could have, according to a group of scientists who offer new evidence that the classic overhand throw used by baseball players at all positions, and by snowball, rock and tomato hurlers of all ages, is an evolutionary adaptation dependent on several changes in anatomy. They first appeared, the researchers say, around 1.8 million years ago, when humans were most likely beginning to hunt big game and needed to throw sharp objects hard and fast.

No other primate throws with anything comparable to human force. Chimpanzees, who are much, much stronger, pound for pound, than human beings, can throw, as any zoo visitor knows. But the best an adult male can do is about 20 miles per hour. A 12-year-old human pitcher can easily throw three times that fast.

Clearly, the reason is not muscle strength, according to Neil Roach of George Washington University, first author of a report in the journal Nature released on Wednesday. Dr. Roach, who conducted the research as a graduate student at Harvard, and his colleagues there used motion-capture video to analyze the throwing motion of 20 college athletes, who hurled baseballs at a target about 100 feet away, with and without a brace that restricted shoulder motion.