New Delhi, Dec. 3: A chance event in the genome of a marine creature about 550 million years ago triggered the evolution of intelligence and brain disorders, from autism to mental retardation to schizophrenia, new research suggests.
Scientists in the UK have identified what they believe was a landmark event in the history of evolution that set off biological changes that led to learning and complex behaviour in simple animals and eventually into the intelligence observed in humans.
The researchers have used a combination of genome studies and laboratory experiments to show that, in both mice and humans, the same genes involved in higher intelligence also play a role in brain disorders. The results of the studies are described in two papers published in the journal Nature Neuroscience on Sunday.
“Mental illness appears to be the price of higher intelligence,” said Seth Grant, professor of molecular neuroscience at the University of Edinburgh who directed the research.
“If we didn’t have these genes (for higher intelligence), we couldn’t do the complex behaviours, and we wouldn’t have the genetic susceptibility they confer to mental illness,” Grant told The Telegraph.
Scientists have long assumed that a steady increase in both the size and the complexity of central nervous system and the brain translated into increasing capacity for intelligence, but the molecular events driving this evolution have remained unknown.
The studies by Grant and his colleagues suggest that a marine invertebrate creature acquired extra copies of a set of ancestral genes that over time led to the emergence of complex behaviour in vertebrates.
“The extra genes could have contributed to an expansion or to a diversity of complex forms of learning or behaviour,” Grant said. “The behaviour could have been something as simple as responding to specific changes in the environment.”
The scientists studied a set of genes called Dlg that help make proteins that serve as scaffolds that bind molecules at the junctions of brain cells to enzymes.
Their studies show that Dlg genes in both mice and humans are involved in higher intelligence tasks such as memory storage and retrieval, processing complex information, and decision-making.
They found mutations or damage to some of these genes appeared to be associated with impaired brain functions.
Mice, for example, that lacked a Dlg gene appeared to show impaired cognition similar to that observed in patients with schizophrenia, the researchers observed.
Two years ago, Grant and his colleagues had reported that one of the genes linked to higher intelligence is known to be mutated in autism.
The scientists believe a better understanding of the shared genomic mechanisms in mice and humans will help in the search for new treatments for brain disorders.