An article in the Washington Post reports on some research by Holly Dunsworth of the University of Rhode Island on the biomechanics of throwing. The research in the original article in Nature seemed to focus on the human predation aspect of throwing.
I have discussed with friends, and wrote, about how early humanity was dependent on throwing rocks for their own protection, and that throwing was a critical skill needed for their development as terrestrial hominids. Others writing on this subject usually support the idea that people developed their throwing abilities for hunting game. Our ancestors did that too, and some point, but it was much later in hominid evolution. To counter this idea that hominids hunted small game first, we may look to chimps and quickly observe that their throwing is limited to acts of aggression against competitors, and occasionally in the form of throwing things, shit usually, down from trees to drive their predators away. Neither of these activities requires much power, or velocity, or accuracy, or forethought, and they offer little evolutionary forcing pressure for physical or mental adaptation.
Humans have developed terrific throwing ability, compared to every other primate, both in power and in accuracy. Baseball pitchers have been recorded reaching over 90 mph with good accuracy, but chimps can only throw at 20 mph, and they have little or no idea of which way their thrown missiles will go. Humans have developed this throwing capacity adaptation with genetic coding. That evolution was formed by what worked best for what they were trying to do, and that was obviously from the adaptation achieved to throw at high velocity and accurately. But why would they need to develop this ability?
Our early hominid ancestors were mostly fruit eaters, being forced to travel on the ground occasionally between fruit trees, and at that time they would be easy prey for lions and other surface-bound predators. However, if they traveled as a group and carried rocks of suitable size for throwing, they could, as a group throwing rocks, get some hits on the big cats. This would keep the cats at bay as long as the rocks were available. As a natural occurrence the hominids would be raising their arms into a throwing position and the lions would soon learn to associate that raised arm activity with their being hit with a stone, and learn to back away even before being hit.
Our ancestors probably started by fending off predators long before they developed the high degree of throwing skill necessary to hit small prey hard enough to be injured by a thrown stone. When in the open, the hominids would be at constant risk of becoming prey themselves, and that would be more critical on a survival basis than an occasional small game dinner. Thus, their problem would be survival first, which had been achieved successfully by their ancestors living mostly in or near fruit trees, but at a low total population. Then with an evolving rock-throwing ability they would be able to go further across open space to more remote fruit trees and the total species population would be able to increase. Also, by traveling to more places they could begin to occupy more varied environments, and more peripheral ones too, and in these distant places there would arise opportunities for splitting off into separate groups and eventually separate species. Even today a few million years later there might be traces of this activity. When traveling across open areas it would be necessary to carry stones for throwing at predators when they came along. It would help to leave a trail of piled throwing-stones, so they wouldn’t have to carry more than a few stones at any one time, and eventually there would be trails of stones between the good places. Perhaps these trails, or small piles of stones might still be found, and dated.
To evolve into a good throwing species our species needed a good grip, which is helped with a forward moved opposable thumb, but far more important for protection to be gained by high velocity throwing was a shoulder to hand muscle and full body arrangement which permitted a whipping motion to be imparted to the hand and the objects held in it. Also, to maximize the power and accuracy required for throwing, the neuro-musculature must be timed with a millisecond accuracy in a coordinated sequence. As a corollary to throwing, developing accurate sequential bodily muscle timing, a similar timing is necessary for developing language and both of these would probably have an overlapping heritable component in the brain’s timing of these events.
Fortunately, this complex set of needed qualities was not totally dependent on simple natural selection but would be helped along by an advanced form of sexual selection, as the early form of artificial selection practiced by evolving hominids. It required only the members of a group observing who was the best at throwing stones and at driving off predators and preferentially breeding with these more valuable members of their group. Accurately throwing sticks and stones at personal competitors and hitting them would also give accurate throwers an advancement in social dominance and thus more breeding possibilities. Thus the complex of DNA necessary to develop these hominid abilities would be developed and maintained. This throwing trait appears in modern boys, and they seem to have an inherent joy in picking up stones and throwing them.
This approach to human ability to throw stones or other missiles at large predators would evolve long before the greater skill needed to hit small game. The throwing skill of Neanderthals may have been poor compared to modern humans because of their relatively short and muscular arms. The common occurrence of healed broken-bone injuries of Neanderthals implies direct physical contact with large animals that would come from using thrusting spears and rocks for killing the animal. Had they been able to throw spears sufficiently hard and accurately to severely injure big game they would have done so, to avoid getting injured themselves. It would seem reasonable that Neanderthals could throw well enough to force approaching predators to back off, because that requires only a few solid hits with a stone, and not a much higher velocity killing throw of a sharp stick. There are several things that helped human evolution advance rapidly. The ability to observe who could drive off predators would be among the more important ones and thus:
Throwing hard and accurately was a driving force in human evolution.