Top baseball pitchers owe much of their success to their early mammoth-hunting ancestors, a study has shown.
Humans evolved unique throwing skills some two million years ago to help them fell and kill wild beasts, say scientists. Today, the same ability that easily outperforms the much stronger chimpanzee can be seen in baseball players and javelin athletes.
Features that boosted the "slingshot" power of shoulder muscles first appeared in an early forbear of modern humans called Homo erectus, a new study suggests. Hunting activity intensified at this time, leading scientists to link it to the physical changes that assisted throwing.
US researchers used a 3D camera system to analyse the throwing motions of baseball players. They found that the human shoulder acts like a slingshot during a throw, storing and releasing large amounts of energy.
"Chimpanzees are incredibly strong and athletic, yet adult male chimps can only throw about 20 miles per hour - one-third the speed of a 12-year-old little league pitcher," said lead scientist Dr Neil Roach, from George Washington University.
"When humans throw, we first rotate our arms backwards away from the target. It is during this 'arm-cocking' phase that humans stretch the tendons and ligaments crossing their shoulder and store elastic energy. When this energy is released, it accelerates the arm forward, generating the fastest motion the human body produces, resulting in a very fast throw."
All this was made possible by a range of anatomical features that evolved together in Homo erectus around two million years ago, he said. They included the lowering and widening of the shoulders, the expansion of the waist and a twisting of the upper arm bone.
Dr Roach added: "We think that throwing was probably most important early on in terms of hunting behaviour, enabling our ancestors to effectively and safely kill big game. Eating more calorie-rich meat and fat would have allowed our ancestors to grow larger brains and bodies and expand into new regions of the world - all of which helped make us who we are today."
Professor Daniel Lieberman, from Harvard University, who co-authored the research published in the journal Nature, said: "The ability to throw was one of a handful of changes that enabled us to become carnivores, which then triggered a host of changes that occurred later in our evolution.
"If we were not good at throwing and running and a few other things, we would not have been able to evolve our large brains, and all the cognitive abilities such as language that come with it. If it were not for our ability to throw, we would not be who we are today."