The human brain is often described using literally cosmic superlatives. Here is V.S. Ramachandran, a renowned neuroscientist:
The human brain, it has been said, is the most complexly organised structure in the universe and to appreciate this you just have to look at some numbers. The brain is made up of one hundred billion nerve cells or "neurons" which is the basic structural and functional units of the nervous system. Each neuron makes something like a thousand to ten thousand contacts with other neurons and these points of contact are called synapses where exchange of information occurs. And based on this information, someone has calculated that the number of possible permutations and combinations of brain activity, in other words the numbers of brain states, exceeds the number of elementary particles in the known universe.That's some serious complexity there, yes, but hidden in the description is a mundane reality: the human brain is made of neurons which make synapses with other neurons, which means that it's made of the same stuff as the brain of a sloth or a goldfish or an earthworm. (Or even a parasitic mite on an earthworm.) Still, whether or not the human brain is really special or just big, something has caused it to grow in ways that differ from its predecessors. Especially at key junctures in the process, human brain development must depart from boring old mammalian brain development. And this should be reflected by — and perhaps explained by — patterns of gene expression.