Why can humans throw so fast? Because of several biological changes.
To be able to throw, it is necessary to be able to grip the projectile, and then have the elasticity in the muscles to fire it. This rules out all animals that can’t grip a projectile. Some primates have the ability to throw, but they cannot throw very far and they cannot throw with much accuracy. Some chimpanzees have been observed throwing rocks at trees and Japanese macaques throw rocks, but they do so underarm and not very accurately. Chimpanzees are far stronger than we are, but the fastest they can throw is about 30 km/h, which is not terribly fast, and they have to be trained to be able to do this. Some monkeys also famously throw their poo, although fling might be a better word to use.
So, why can humans throw so fast? We have several evolutionary advantages when it comes to throwing. Throwing gave early humans the ability to hunt and to kill prey at a distance. We are not fast enough to run after prey (running down animals over long distances excepted), which means most animals were out of the range of early humans. However, we did have the ability to kill them with a rock or a spear. The evolutionary changes that led to us being able to throw so fast came from that origin. Somebody who could throw could get more food and was more likely to mate, passing the throwing trait on.
What evolutionary traits have left us able to throw so fast and so far? The first advantage is being able to walk on two feet. We started to do that anywhere from 4 million to 1 million years ago and we lost our tails at the same time. As we became upright, our center of balance also changed. Chimpanzees have a lot of trouble throwing because they cannot get all of their body behind the throw. When they are upright, their center of balance doesn’t allow them to be stable enough. This is caused by a curve in our lower backs called the lordosis. It positions our upper bodies over our legs and primates don’t have this. Walking on two feet also freed up our hands for other jobs such as using tools and throwing things.
The second evolutionary trait is our waists. Our waists are able to rotate far more than other primates because of the way it connects to our hips and upper body. This rotational ability allows us to twist back, putting more momentum into the projectile we are throwing. The third change was the position of our shoulders. Chimpanzees have a shoulder joint that is almost diagonal and attaches the shoulder much higher up on the chimp’s body, closer to the neck. Our shoulder joints are closer to horizontal and attach the shoulder a little lower down. This aligns the upper arm more closely with the chest muscles, giving us a greater range of motion than chimps have.
The fourth change is the ability of our humerus bone to twist. When we use our arm to throw, we have to rotate it extremely quickly to fling the projectile. The rotation of the humerus is the fastest motion in the human body and it rotates at a speed which is equivalent to twenty-five rotations in a second.
So, why can we throw so fast? All of these evolutionary traits combine to allow us to store energy in our muscles and shoulders. When we throw, we pull our arm back and we twist the humerus. Our waists allow us to twist even father back. We keep our center of balance and reach our arms far back. This movement stretches the muscles, ligaments, and tendons across the soldier, basically like a giant elastic band. When we are ready to throw, we release and the whole system unwinds, like a slingshot.
Being able to throw fast isn’t great if you can’t hit what you are throwing at. When we started being able to kill more prey, the increase in a reliable food source allowed our brains to increase in size. The part of the brain concerned with throwing, targeting, and eye movement is the cerebellum. The cerebellum grew as our diet improved, and our skill at throwing improved. So, thanks to all of these evolutionary advantages and a larger brain, we are able to throw faster, farther, and more accurately than any other animal. And this is what I learned today.
Sources
https://www.pbs.org/wgbh/evolution/library/07/3/text_pop/l_073_08.html
https://pubmed.ncbi.nlm.nih.gov/25283776/
https://www.bbc.com/future/article/20140225-human-vs-animal-who-throws-best
https://www.nytimes.com/2013/06/27/science/evolution-on-the-mound-why-humans-throw-so-well.html
https://theconversation.com/how-humans-became-the-best-throwers-on-the-planet-131189