How often do we hear that humans only use 10% of their brain? “Imagine what humans would do if they used a greater part of their minds!”
Yet there has been a species with a larger brain than the human one, Homo neanderthalensis.
The final answer is very simple: the humans don’t use the totality of their brain because they don’t need to; the human brain is larger due to its ontogeny.
It is well known that humans do not use but approximately 10% of their brains and often one asks himself what would happen if a bigger part of the brain were used. But is this something that is possible? Sure, it could happen but it would be due to some physiological dysfunction (or some other similar phenomenon) and it wouldn’t mean that it is the way it should normally function.
The case of the human brain is a nice example for the principle of exaptation. During the evolution of the humanoids, Homo neanderthalensis was the one species that had a larger brain than the one of Homo sapiens (humans). The reason is very simple: the brain was larger because it could. Human brains are quite big as well, for the embryological reason that it was able to grow more. This means that we do not actually need more than the 3/4 of our brain, we just have it because during the early ontogenesis, the nervous tissue of the region of the head gets larger than the one of other animals. It is a passive process that does not consist of a specific adaptation or a need. Indeed, it is quite useless to have such a large brain since humans -and much more neanderthals- do not even use half of it. But the organism is not able to find a way to use it from a physiological and histological point of view.
The large brain that we are so proud of is therefore something that we only have a partial use for, and from the moment that we know that, the myth that we could be much smarter if we could use more than 10% of this organ seems irrelevant.