Why are the majority of people right handed? No one knows for definite, but it could be because we process language with the left side of our brain.
It is generally thought that 85 to 90% of people are right-handed. The majority of the rest are left-handed, with a very few individuals being ambidextrous. A species-wide dominant hand is unique to humans. All animals will have a dominant hand or a dominant paw, but it is random, depending on that animal. It is not the case that more of a certain species are right-pawed than left-pawed. Chimpanzees, who are said to be our closest relatives, don’t have a preference for a particular hand and are just as comfortable holding tools in either one. When they are forced to stand up on two legs, they do choose one hand over the other, but the right hand is no more common than the left hand. Yet, humans do have a preference. What could have caused it?
The right hand being dominant seems to have started between about 1.5 million and 600,000 years ago. Stone tools that were made 1.5 years ago in Kenya are more often made for the right hand than they are for the left, but not enough to show that one hand is dominant. However, fossils found from 600,000 years ago do show that the right hand is dominant across the species. The best way would be to find the fossils of arm bones and work out which of the two is stronger, because the dominant arm will become slightly larger, but it is very rare to find two arm bones from the same skeleton. Teeth are much more common and experts can tell which hand is dominant from the teeth because those on one side of the skull are more worn than the other, which indicates that they used their right hand to hold their food with. The oldest jawbone found with marks on the teeth is 1.8 million years old, but by 600,000 years ago, almost all the jaws found have marks on the same side.
What could have occurred around this time that would have caused right-handedness to become dominant? There is no way of knowing the actual reason, but there are some theories. The most likely reason is that our brains developed beyond those of other animals and we began to use different parts of our brains for specialist activities, plus the fact that the right and left hemispheres of our brains control the opposite sides of our bodies.
This is another thing that nobody really knows the reason for, but our nervous system is twisted so that the left side of our brain controls the right side of our body and the right side of our brain controls the left side of our body. This twist is common to all vertebrates, so it must have happened to a common ancestor we all share. At some point, that common ancestor turned its head around and twisted up its nerves. The reason seems to be that the creature wanted to swap the location of its nervous system from underneath its organs to above them. Insects still have their nervous system underneath their organs, while all vertebrates (even us if we go on all fours) have their nervous system on top of their organs. This obviously presented enough of an evolutionary advantage that it was passed on to all vertebrates. But what that means is that we use the opposite sides of our brains to control our body.
Why would that lead to most people being right-handed? The idea is that around the time most people became right-handed, humans began to develop language. Our brains were growing larger, for many reasons, and at some point, we began to communicate with each other. We would have started by making sounds to mimic real things, such as many animals do today. Then the number of sounds would have gradually increased until the sounds started to take on different meanings or concepts. There are only so many sounds that we can memorize, so these sounds became words, and grammar followed because you can say far more with a language than you can with just sounds. All of this began when we became right-handed and this right-handedness could be a byproduct of language because language is generally processed in the left side of the brain. Processing language and speaking is such a huge energy requirement that the brain may have evolved to process other things in the right side of the brain, such as sight and hearing. Because the left side evolved to process language and govern the fine motor control needed for speech, it was able to control the arm it was in charge of, the right, with more skill, making it more dominant. Then, once we have a dominant arm, it becomes more dominant through reinforcement. The only problem with this theory is that most left-handed people also process language with the left side of their brain. And this is what I learned today.
Photo by Kindel Media: https://www.pexels.com/photo/a-person-holding-a-pen-7054514/
Sources
https://www.bbc.com/future/article/20141215-why-are-most-of-us-right-handed
https://www.latrobe.edu.au/news/articles/2017/opinion/why-are-most-people-right-handed
https://www.socsci.uci.edu/newsevents/news/2022/2022-08-08-futrell-when-was-talking-invented.php
https://www.discovermagazine.com/the-sciences/when-did-humans-evolve-language
https://academic.oup.com/brain/article/123/12/2512/325690