Mental illness and Intelligence tied to ancient accident

Scientists have discovered for the first time how humans – and other mammals – have evolved to have intelligence.

Researchers 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, analyse situations and have flexibility in the way in which we think.

Professor Seth Grant, of the University of Edinburgh, who led the research, said: “One of the greatest scientific problems is to explain how intelligence and complex behaviours arose during evolution.”

The research, which is detailed in two papers in Nature Neuroscience, also shows a direct link between the evolution of behaviour and the origins of brain diseases.

Scientists believe that the same genes that improved our mental capacity are also responsible for a number of brain disorders.

“This ground breaking work has implications for how we understand the emergence of psychiatric disorders and will offer new avenues for the development of new treatments,” said John Williams, Head of Neuroscience and Mental Health at the Wellcome Trust, one of the study funders.

Genetic accidents will happen

The study shows that intelligence in humans developed as the result of an increase in the number of brain genes in our evolutionary ancestors.

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 behaviourally 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.

Researchers then combined results of these behavioural tests with information from the genetic codes of various species to work out when different behaviours evolved.

Mental illness connection

They found that higher mental functions in humans and mice were controlled by the same genes.

The study also showed that 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 Professor Grant.

The researchers had previously shown that more than 100 childhood and adult brain diseases are caused by gene mutations.

“We can now apply genetics and behavioural testing to help patients with these diseases”, said Dr Tim Bussey from Cambridge University, which was also involved in the study.

Antidepressants in water trigger Autism genes in fish

Low levels of antidepressants and other psychoactive drugs in water supplies can trigger the expression of genes associated with autism, in fish at least.

The use of antidepressants has increased dramatically over the past 25 years, says Michael Thomas of Idaho State University in Pocatello. 

Around 80 per cent of each drug passes straight through the human body without being broken down, and so they are present in waste water. In most communities, water purification systems cannot filter out these pharmaceuticals. 

"They just fly right through," says Thomas, which means they ultimately find their way into the water supply.

The concentration of these drugs in drinking water is very low – at most, they are present at levels several orders of magnitude lower than the prescription doses. 

But since the drugs are specifically designed to act on the nervous system, Thomas hypothesised that even a small dose could affect a developing fetus.

Thomas's group created a cocktail of the anti-epileptic drug carbamazepine and two selective serotonin uptake inhibitor (SSRI) antidepressants, fluoxetine and venlafaxine, at this low concentration. 

They exposed fathead minnows (Pimephales promelas) to the drugs for 18 days, then analysed the genes that were being expressed in the fishes' brains.

Although the researchers had expected the drugs might activate genes involved in all kinds of neurological disorders, only 324 genes associated with autism in humans appeared to be significantly altered. Most of these genes are involved in early brain development and wiring.

The finding fits with previous research which had found that pregnant women who take SSRIs are slightly more likely to have autistic children. (Archives of General Psychiatry, DOI: 10.1001/archgenpsychiatry.2011.73).

To test whether these changes actually altered the fish's behaviour, the researchers did an experiment in which they startled the fish. Fish exposed to the drugs tended to panic and behave differently from a control group of fish.

Thomas emphasises that the research is very preliminary – there's no need for pregnant women to worry about their drinking water yet, he says. The researchers next plan to study whether the drugs have a similar effect in mammals. 

They are testing this by lacing the drinking water of pregnant mice with the low-concentration cocktail. 

They are also studying water supplies in areas around the country where there are particularly high concentrations of drugs to determine whether the fish – and people – in these areas have autism-like gene expression patterns.

Journal reference: PLoS One, DOI: 10.1371/journal.pone.0032917