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."