Baseball pitchers are living examples of a breakthrough moment in human evolution, when our ancestors evolved accurate high-speed throwing ability, leaving most other primates behind in the trees.
The secrets behind our throwing success, documented in a new Nature study, help to explain why chimpanzees and other non-human primates would strike out on the baseball field, and why humans today aren't great tree swingers.
It appears that our ancestors traded climbing ability for throwing skills.
"Tree climbing requires large, powerful muscles with different demands on force production and perhaps reduces the range of motion at the shoulder and precludes the kind of throw that a baseball pitcher does," said co-author Madhusudhan Venkadesan, an assistant professor at the National Center for Biological Sciences in India. "Also, becoming proficient bipedal animals forced our ancestors to evolve mobile waists, an adaptation that simultaneously benefits walking or running, and throwing. These arguments suggest a trade-off between throwing and climbing."
Venkadesan and his colleagues used high-speed, 3-D imagery and analysis to study 20 people as they threw a baseball overhead. The researchers determined that human ability to throw largely results from anatomical features that enable elastic energy storage and release at the shoulder. A twisty waist, as Venkadesan indicated, is important as well.
The somewhat human-looking Australopithecus afarensis, which lived between 3.9 and 2.9 million years ago, appears to have had a mobile waist. This evolved to improve walking on two legs and set the stage for future uses.
Those additional uses came into fruition with Homo erectus, aka "Upright Man," which emerged about 2 million years ago. Homo erectus, the scientists believe, was the first human ancestor who could execute accurate, high-speed throws.
"We think they were throwing overhead, and probably spears," co-author Daniel Lieberman, chair of Harvard's Department of Human Evolutionary Biology, told Discovery News. "No doubt they threw other objects as well, such as rocks."
Back in prehistoric days, these throws likely would have meant the difference between supper and starvation. Both males and females evolved throwing ability, even if one sex did most of the active hunting.
Lieberman said that the bodily changes now allow us to throw well. Other primates, conversely, would bomb on the baseball field. Adult male chimps, for example, "can only throw about 20 miles per hour -- one-third the speed of a 12-year-old little league pitcher," lead author Neil Roach of George Washington University pointed out.
Ancient humans weren't throwing all of the time, however, as today's baseball pitchers reveal. Most pro baseball players suffer injuries at some point due to wear and tear.
"To hunt by throwing projectiles, our ancestors clearly had to throw often," Venkadesan said, "but that is probably far fewer throws a day than the hundreds of throws that a baseball pitcher does. I would speculate that it is this difference of frequency in throwing that leads to injuries among pitchers."
"This study uses a solid biomechanical analysis, and the results are well supported by the data," said Thomas Roberts, an associate professor of ecology and evolutionary biology at Brown University, who did not work on the study. "I'm not surprised that springy tendons and ligaments are really important in throwing, but this study shows that this mechanism may be a crucial part of the evolution of the exceptional throwing ability in humans."
Roberts said future research might investigate what the optimal throwing techniques for hu