Why gorillas can't throw fastballs
A team of researchers has found that some 2 million years ago, early humans evolved the ability to aim and throw, skills not shared by our closest living relatives.
It's completely ordinary to see today's athletes throw a javelin hundreds of feet in the air or fire baseballs accurately and in excess of 90 mph dozens of times during a game. However, not every close human relative has that ability to throw, despite the great strength that many possess. Researchers say they traced that ability back to three changes to the waist, shoulder and upper arm that happened about 2 million years ago in the early human Homo erectus.Skip to next paragraph
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Making a strong, accurate throw requires the different parts of the body to work together in what biomechanics researchers call a kinetic chain -- the rapid and sequential activation of different muscles. The motion that launches a throw begins with the legs, moves through the hips, torso, shoulder, and through the arm to the hand. Throwing projectiles fast and with high accuracy requires coordination, and also the anatomical features that first appeared together in Homo erectus.
A team of researchers, reporting in Nature, found that the three key traits can be found in humans, but not our closest relatives, chimpanzees. Each feature allows the body to store more energy before a quick rotation that releases it: tall and mobile waists that permit torso rotation; the way the elbow and the bone in the upper arm, the humerus, join together and rotate; and the placement of the shoulders. Each trait has "a major role in storing and releasing elastic energy during throwing," the researchers wrote.
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The change to the shoulder is crucial, explained Neil Roach, a biological anthropologist at George Washington University in Washington, D.C. While chimpanzee shoulders sit very high and close to the neck, almost as if the animal is permanently shrugging its shoulders, human shoulders are much more relaxed.
"That change in the shoulder really brings all of those things together and that didn't happen until 2 million years ago," said Roach. "That allows us to essentially use the arm like a catapult, to store energy as we cock our arm or rotate our arm away from the target before we rapidly rotate it toward the target."
The rotation of the humerus is the fastest motion the human body produces, said Roach, at over 9,000 degrees per second.
Sending Modern Baseball Players Back in Time
The researchers studied both the fossil record and Harvard University baseball players in order to develop their insights. They used motion capture technology to track the way experienced throwers launch the ball.
The researchers also studied restricted motion using braces, Roach said. They prevented subjects from relaxing their shoulders and restricted the motion of the arm.
"What that did was give us the ability to at least mimic what the ancestral anatomy would have been like," said Roach.
The resulting observations allowed the researchers to zero in on the most important features for throwing: the elbow, shoulder and waist. The fossil record showed that when Homo erectus developed these features together, it made them the first of our relatives that could throw like modern humans.