Robert Sapolsky in the New York Times:
Despite rumors to the contrary, there are many ways in which the human brain isn’t all that fancy. Let’s compare it to the nervous system of a fruit fly. Both are made up of cells, of course, with neurons playing particularly important roles. Now one might expect that a neuron from a human will differ dramatically from one from a fly. Maybe the human’s will have especially ornate ways of communicating with other neurons, making use of unique “neurotransmitter” messengers. Maybe compared to the lowly fly neuron, human neurons are bigger, more complex, in some way can run faster and jump higher.
But no. Look at neurons from the two species under a microscope and they look the same. They have the same electrical properties, many of the same neurotransmitters, the same protein channels that allow ions to flow in and out, as well as a remarkably high number of genes in common. Neurons are the same basic building blocks in both species.
So where’s the difference? It’s numbers — humans have roughly one million neurons for each one in a fly. And out of a human’s 100 billion neurons emerge some pretty remarkable things. With enough quantity, you generate quality.
Neuroscientists understand the structural bases of some of these qualities.