Elastic energy storage in the shoulder and the evolution of high-speed throwing in Homo

Humans are able to throw projectiles with high speed and accuracy largely as a result of anatomical features that enable elastic energy storage and release at the shoulder; features that first appear together approximately 2 million years ago in Homo erectus , possibly as a means to hunt. A strong arm — since the days of Homo erectus ? Darwin speculated that bipedalism might have contributed to humans' unique ability to throw things so well. Although some primates, including our closest relatives — chimpanzees, will throw objects now and then, their throws do not come close to matching the speed and accuracy achieved by even young human boys. Neil Roach and colleagues analysed the biomechanics of collegiate baseball players' throwing motion in order to better understand the evolution of this novel behaviour. Their findings show that adaptations in the human upper body allow us to store and release elastic energy in the shoulder in a catapult-like fashion. Evidence of these key shifts in morphology that make this energy storage possible is preserved in the hominin fossil record. From these fossils, the authors infer that the ability to throw objects with high speed probably arose with Homo erectus , and may have had a crucial role in early hunting. Some primates, including chimpanzees, throw objects occasionally 1 , 2 , but only humans regularly throw projectiles with high speed and accuracy. Darwin noted that the unique throwing abilities of humans, which were made possible when bipedalism emancipated the arms, enabled foragers to hunt effectively using projectiles 3 . However, there has been little consideration of the evolution of throwing in the years since Darwin made his observations, in part because of a lack of evidence of when, how and why hominins evolved the ability to generate high-speed throws 4 , 5 , 6 , 7 , 8 . Here we use experimental studies of humans throwing projectiles to show that our throwing capabilities largely result from several derived anatomical features that enable elastic energy storage and release at the shoulder. These features first appear together approximately 2 million years ago in the species Homo erectus . Taking into consideration archaeological evidence suggesting that hunting activity intensified around this time 9 , we conclude that selection for throwing as a means to hunt probably had an important role in the evolution of the genus Homo .