Why Humans Throw So Well

This is cool.

At the New York Times, "Scientists Unlock Mystery in Evolution of Pitchers":

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.

They analyzed the structure of the shoulder and upper arm, the motion and the forces involved, and concluded, first, that muscles alone cannot account for how hard and fast humans throw. The shoulder and arm and the rest of the body involved in the throwing motion must be storing elastic energy, like the long tendon of a kangaroo when it hops, or the human Achilles’ tendon in running and jumping, they said.

“You’re storing energy in your shoulder,” Dr. Roach said, speaking from Africa, where he was heading to Lake Turkana to look at fossil footprints of human ancestors about a million and a half years old. The storage occurs in the cocking motion, when a thrower brings hand and ball back, preparing to throw. “It works just like a slingshot would. You’re actually stretching the ligaments.”

Several developments in anatomy allowed humans to throw this way, he said, including a waist that allows twisting and a relatively open shoulder, compared with those of other primates like chimpanzees.

Looking at the fossil record, Dr. Roach and colleagues put the moment at which these changes came together in one body at about 1.8 million years ago, when Homo erectus first appeared. “It’s possible that Homo erectus could throw as fast as we do,” Dr. Roach said.

More at that top link.