For years, scientists have looked at the differences between the human and chimp brains primarily in terms of size. A new study by experts at the University of California in Los Angeles (UCLA) indicates that the complexity of neural wiring may be even more important.
Physically, humans and chimps still look remarkably similar, since they originated in the same common ancestor. However, their brains are very different. The human one is larger than that of chimps, but the new study suggests that this is not the main reason why we're smarter than the primates.
In fact, it could be that unique patterns of gene activity in the brain, and the complexity of the neural networks that are formed in our heads, are primarily responsible for our species becoming dominant.
In addition to its anthropological and historic value, the new investigation could also help neurologists gain more insight into the nature of conditions such as schizophrenia, addictions, learning disorders, and autism, the UCLA group believes.
A paper describing the study in detail is published in the August 22 advanced online issue of the top scientific journal Neuron. The principal investigator on the research was Dr. Daniel Geschwind.
“Scientists usually describe evolution in terms of the human brain growing bigger and adding new regions. Our research suggests that it's not only size but the rising complexity within brain centers that led humans to evolve into their own species,” he says.
Geschwind holds an appointment as the Gordon and Virginia MacDonald distinguished professor of human genetics, and as a professor of neurology, at the UCLA David Geffen School of Medicine. He is also a professor of psychiatry at the university's Semel Institute for Neuroscience and Behavior.
“When we looked at gene expression in the frontal lobe, we saw a striking increase in molecular complexity in the human brain,” the team leader goes on to say. He and his team analyzed a series of brain tissue samples, collected post-mortem.
When comparing human and chimp genes, researchers found the biggest differences in the expression patterns of genes underlying neural plasticity. This is a property of the brain that enables it to adapt to new demands by breaking previous synapses, and forming new ones.
This capability allows us to learn new things at a fast pace, and to be able to change from being specialized in one action to being specialized in another, according to necessities.