The Evolution of Throwing: How Humans Toss a Fast Ball

Throwing may not seem very difficult. Even children can toss a ball, and every parent is well aware of a toddler's ability to throw the nearest object onto the floor. Yet no other creature in the animal kingdom can throw as well as a human. Now, scientists have studied the fine art of throwing and have discovered exactly how we evolved this unique adaptation.

In order to learn more about the evolution of human throwing, scientists turned to our closest living relatives: chimpanzees. These animals are known to throw objects (often feces) underhand. Only rarely will they throw overhand--and these throws are far less accurate and powerful than those of a baseball pitcher.

"Chimps throw overhand using either a dart throwing motion, where the elbow is extended, or much like a cricket bowler, where the elbow is kept straight and they generate force by swinging their shoulder," said Daniel Lieberman, one of the researchers, in a news release. This technique in combination with the chimp's anatomy keeps it from throwing as hard or as accurately as a human.

After examining chimps, the scientists were ready to move onto humans. They created a complex model that incorporated current research about the biomechanics of throwing and used it to explore how morphological changes to the body effect throwing performance. The researchers also conducted a series of real-world experiments with a baseball team, watching how a host of different braces affected their throwing performance.

"We try to push these bits of anatomy back in time, if you will, to see how that affects performance," said Neil Roach, one of the researchers, in a news release. "The important thing about our experiments is that they went beyond just being able to measure how the restriction affects someone's ability to throw fast and accurately--they allowed us to figure out the underlying physics. For example, when a thrower's velocity dropped by 10 percent, we could trace that change back to where it occurred."

It turns out that evolutionary changes in the shoulder are the main cause of a human's throwing ability. More specifically, a person can cock their arm back, stretching the ligaments and tendons that run across their shoulder--rather like an elastic band on a slingshot. The resulting rotation is the fastest motion that a human body can produce.

"The linchpin is really what's going on with the shoulder," said Roach in a news release. "When you see the shift from a chimpanzee shoulder to a more relaxed human-like shoulder, that enables this massive energy storage. Many of the evolutionary changes we studied, whether in the torso or the wrist, may predate Homo erectus, but when we see that final change in the shoulder, that's what brings it all together."

The findings not only reveal the evolutionary changes in humans, though. They also may answer a sports-related question: How much throwing is too much? From an evolutionary perspective, this is easily answered. Our forebears had to throw spears often to hunt--but not nearly as often as pitchers need to throw a ball during the course of a game. Athletes, in other words, are essentially overusing this ability--an adaptation that is uniquely human.

The findings are published in the journal Nature.

Want to learn more? Check out the video here.