The brain’s lopsidedness is most evident through our hand preferences. Roughly nine out of every ten people are right handed. Lefties are indeed a rarity. And these figures hold across all human populations and cultures showing that it’s a universal pattern for Homo sapiens, being genetically hardwired.
Below the surface, these statistics about right versus left handedness reveal something rather peculiar about human brains: the left hemisphere generally dominates over the right when it comes to controlling the movements of the hands. And this hemispheric dominance – or asymmetry – is unique.
Similar patterns can be seen for the language areas of the brain as well. Regions on the left side such as Broca’s Area – which play a vital role in language production and comprehension – are disproportionately enlarged, lopsided even, compared with their right side equivalents.
In fact, Broca’s Area is six times larger than the same region on the right side of the brain when compared with a chimpanzee’s noggin. That’s twice as large as you’d expect based on our threefold larger brains.
Another way the human brain is lopsided is the misalignment or even skewness between the left and right hemispheres themselves, a feature called petalias. When seen from above, the front most part of the right hemisphere juts further forward than the left. And the opposite configuration is seen on the left side, where the rear of the left hemisphere projects further back then the right.
A similar pattern is seen in the brains of other apes and even some monkeys, but it’s nowhere near as striking as in the human brain. And petalias are also seen in the arrangements of the blood vessels that supply and drain the brain and can even be observed on a microscopic level.
What role do petalia’s play? Well again they seem to be a part of the overall asymmetry of the human brain, whereby functions are relegated to a particular side, much like we see with hand control or language.
If our cockeyed brains are so unique, then why did they evolve to be this way?