Genetic 'overdrive' that made the human brain special is discovered

Humans went into evolutionary overdrive as their brains developed, sending them on a path that set them apart from other animals, scientists believe. Researchers who studied the rate of change in the human brain concluded that Homo sapiens really is special.

Human progress was driven by unprecedented natural selection pressure and an explosion of genetic mutations in the brain, the scientists found. Far from being just a more complex form of ape, humans occupied a unique place in the "tree of life".

Many researchers had thought the human brain evolved in processes inherently no different from those that led, for instance, to the development of larger antlers or longer tusks.

"We've proved there is a big distinction," said Bruce Lahn, assistant professor of human genetics at the University of Chicago. "Human evolution is a privileged process because it involves a large number of mutations in a large number of genes. To accomplish so much in so little evolutionary time - a few tens of millions of years - requires a selective process perhaps categorically different from the typical processes of acquiring new biological traits."

The Chicago scientists examined the DNA of 214 genes involved in brain development and function in four species, humans, macaque monkeys, rats and mice. They found brain-related genes evolved much more swiftly in humans and macaques than in rats and mice, and at a higher rate in humans than in monkeys. Brain development in humans also evolved more quickly than in our closest cousins, the chimpanzees, the scientists reported in the journal Cell.

Dr Lahn said: "The making of the large human brain is not just the neurological equivalent of making a large antler. It required a level of selection that's unprecedented. Our study offers the first genetic evidence that humans occupy a unique position in the tree of life. Simply put, evolution has been working very hard to produce us humans."