Editorial: Evolutionary Advantage; The Arm Gave Us a Leg Up

Even the most casual fan knows that good pitching is essential to winning baseball, but who knew that it was also key to human evolution?

Just such a proposition was put forth last week by a team of scientists whose report appeared in the journal Nature.

They suggested that several changes in anatomy that first appeared about 1.8 million years ago gave early humans a singular advantage in throwing just as they were beginning to hunt big game with spears, rocks and other projectiles. This evolutionary adaptation, in turn, may have led to an improved diet for our ancestors, providing more protein and leading to larger bodies and bigger brains, and eventually, we suppose, to the 95 mph fastball.

In fact, no other primate is capable of throwing objects with anywhere near as much force as humans. For example, chimps, our closest relatives, who share 98 percent of our DNA, touch only 20 mph on the radar gun. (So despite the fact that chimps are physically superior to humans in most respects, no manager is going to call in the chimp from the bullpen when the game is on the line.)

Specifically, the researchers attributed this ability to throw hard and accurately overhand to critical changes in human anatomy: longer waists that allow torso rotation, shoulders that moved lower on the torso, and an upper arm bone that twists, allowing the thrower to reach back at an unusual angle. These changes allow the storage of elastic energy. And when that energy is released in the classic overhand throw, the upper arm rotates forward at 9,000 degrees per second (in a big league pitcher), which the study says is the fastest motion the human body is capable of producing.

As The Washington Post reported, the study is far from the first to examine humans’ throwing motion as a key to evolution. In fact, Darwin took note of it and suggested that this ability was developed when early humans stood up on two legs, thus freeing their arms and hands for hunting. But the new work does tie the theory of biomechanical changes in throwing to the fossil record on hunting, and thus is drawing praise in scientific circles.

Of course, the study does not answer all the questions to which it gives rise. First, if humans developed a unique ability to throw fast and accurately, why do so many people — how to put this delicately? — “throw like a girl”? The answer does not lie in anatomical differences; many females throw hard and fast in classic fashion. But not everyone practices, and therefore develops, the innate human ability to throw.

Second, if the human body was made to throw, why do so many pitchers suffer shoulder injuries? It’s not because throwing isn’t natural, Glenn Fleisig, research director of the American Sports Medicine Institute in Birmingham, Ala., told The New York Times. “What’s not natural is throwing a hundred pitches from a mound every fifth day,” Fleisig said. We suppose that any of our ancestors who had to throw a spear a hundred times in one day in the pursuit of game had a pretty good chance of starving before suffering a career-threatening shoulder injury.

Finally, why do shoulder injuries hurt so much? We’ll take two aspirin now; call us in the morning.