So why did humans acquire this talent? Throwing probably gave our early ancestors a better chance of acquiring a meal, and wouldn't have been possible without various skeletal and anatomical adaptations that allowed for the rotation of the arm and pelvis. But it is also possible that throwing was a communicative gesture, as it seems to be for Japanese macaques. That's perhaps why some have argued that more accurate throwing helped to usher in a host of cognitive advances, including language and music. After all, throwing requires a certain amount of psychological sophistication.

To better understand the evolution of throwing, psychologist Justin Wood wondered whether the he could separate the anatomical requirements for aimed throwing (that is, the "hardware") from the psychological operations that guide it (the "software"). To do so, he turned to rhesus macaques. These monkeys share the anatomy of Japanese macaques, so if they did throw, it would be fairly haphazard. But to what extent do they “understand” the act of throwing? Would they still retreat from a human experimenter that seemed to throw a rock at them? (The researchers never actually released the rock; the monkeys were never in any actual danger of being struck or injured. In truth, an angry rhesus monkey would be a bigger danger to a human.)

While 85% of monkeys ran away when the researchers completed the throwing motion, far fewer bothered to retreat when the trajectory, speed, or direction of the throwing arm were such that the throw would not be dangerous. They also didn't care about completed overhand throws if they were done with an empty hand or while holding a bit of soft food. In other words, despite being unable to throw accurately, they possessed the requisite mental machinery to accurately evaluate the possible trajectory of thrown objects, and to determine whether they were in danger of being struck.

That suggests that at least some of the psychological prerequisites for accurate throwing were present among our primate ancestors, long before the requisite skeletal and muscular anatomy evolved in our hominid ancestors to make it possible.

Our short fingers and other adaptations within the structure of our hands seem to have defined our species in the same way as a bipedal stance and enlarged skulls. Those changes in hand anatomy gave rise to more powerful and precise hand motions, according to hand surgeon Scott Wolfe. "The ubiquitous presence of the dart-thrower’s wrist motion in distinctively human activities involving tool use, throwing, and weaponry suggests that its development also may have played an important role in human evolution."