Evolution is simply the sum of microscopic changes over the millennia. Primates have smaller brains, fewer neurons, but what makes them different is the way the neurons are distributed.
As mentioned above, most of the neurons are distributed in the cerebellum and cortex. However, their density distribution in any regions is not the same, or in other words is asymmetric. And here is the answer to the question posed in the article title.
Why is size not important?
Suzana Herculano-Houzel – a Brazilian neuroscientist – and her students conducted an experiment to count the number of neurons in the brain of an African elephant, specifically the number of neurons located in the cortex ( especially the prefrontal cortex) – which she believes is the source of intelligence. She used a knife to cut the elephant’s brain into parts and count the number of neurons on each part. According to her prediction, although the elephant’s brain is large, the density of neurons in the cerebral cortex will be much lower than that of humans, and it is the density of neurons that determines the intelligence level of an organism, not the the size of the brain regions in which those neurons reside. And that is exactly what she discovered after the elephant brain surgery experiment: the total number of neurons in the elephant’s brain is about 257 billion, 3 times higher than the figure of 86 billion of the human brain. However, 98% of those 257 billion neurons are in the cerebellum, with only 5.6 billion in the cortex. In humans, in our cerebral cortex there are up to 16 billion neurons!
Suzana’s experiments have shown that human intelligence comes from the enormous density of neurons in the cerebellum, instead of the cerebellum. The number of human cortical neurons outstrips all other living things on this planet!
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