Neuroscientists think they have some insight for evolutionary biologists into how humans, and other mammals, have evolved to have intelligence. They say they have identified the moment in history when the genes that enabled us to think and reason evolved.

This point 500 million years ago provided our ability to learn complex skills, analyze situations and have flexibility in the way in which we think, says Professor Seth Grant of the University of Edinburgh, who led the research -  "One of the greatest scientific problems is to explain how intelligence and complex behaviours arose during evolution." 

They say their research also shows a direct link between the evolution of behavior and the origins of brain diseases and that the same genes that improved our mental capacity are also responsible for a number of brain disorders.

Intelligence in humans developed as the result of an increase in the number of brain genes in our evolutionary ancestors, that is obvious, but the researchers suggest that a simple invertebrate animal living in the sea 500 million years ago experienced a 'genetic accident', which resulted in extra copies of these genes being made. This animal's descendants benefited from these extra genes, leading to behaviorally sophisticated vertebrates – including humans. 

The research team studied the mental abilities of mice and humans, using comparative tasks that involved identifying objects on touch-screen computers. They then combined results of these behavioral tests with information from the genetic codes of various species to work out when different behaviors evolved.

They found that higher mental functions in humans and mice were controlled by the same genes. When these genes were mutated or damaged, they impaired higher mental functions. 

"Our work shows that the price of higher intelligence and more complex behaviours is more mental illness," said Grant.


Published in two papers in Nature Neuroscience.