Researchers bust head size-intelligence link
The genes that are thought to have helped humans evolve big brains do not appear to play any role in how intelligent we are, according to a DNA study.
This backs separate research that has failed to come up with a link between head size and intelligence, except in extreme congenital abnormalities.
The Queensland Institute of Medical Research (QMIR) study is the first to specifically look at genes, head size and intelligence in a normal population.
The Australian study finds that people who scored highly in intelligence tests did not necessarily possess versions of the genes that are expected to code for big heads and intelligence.
People who did possess the suspected 'smart' versions of the genes were not necessarily the most intelligent or the ones with the biggest brains.
The study will be presented at the 11th International Congress of Human Genetics in Brisbane next week.
The researchers tested 4,395 teenagers for head size and intelligence.
They also looked at the genes ASPM, MCPH1 and CDK5RAP2, which regulate brain size and activity.
When mutated, these genes result in an abnormally small brain, a condition known as congenital microcephaly.
"Normal variation in these genes has not yet been investigated in relation to head size and intelligence," Dr Michelle Luciano, a research fellow at QMIR, said.
She says the only comparable previous study used MRI imaging to measure brain volume in relation to two microcephaly genes.
"Their findings [about a relation to brain size] were negative and they didn't find a relationship with two of the genes we were looking at," Dr Luciano said.
"We decided to take it a step further and look at intelligence and lo and behold we find a similar negative result."
Ancestral or evolved?
We all carry the three genes the QMIR team investigated but some of us carry 'ancestral', or less evolved, versions and others carry 'derived' or more recently evolved versions.
Some of us carry one of each.
Dr Luciano says researchers had expected that people with evolved versions of the gene would be smarter and have bigger heads, but were surprised to find this was not the case.
"We would predict that if you've got the more recent version you should have a higher IQ," she said.
"We actually found that not to be the case.
"It is unlikely then that selective pressure for these genes is related to the evolution of intelligence in humans."
Rather, she says the genes might be important for a neurological function outside the brain.
Are humans getting smarter?
Professor Colin Groves, an expert in human evolution from the Australian National University, says human brains began getting bigger after our earliest ancestors like Homo habilis appeared.
But our brains have stopped growing and have actually started getting smaller, or at least more 'compact'.
"[Our brains] have got bigger but they're not getting bigger," he said.
"In fact since the late Pleistocene in general they've got smaller."
Professor Groves says while brain size appears to be related to intelligence between species, this does not seem to be the case within a species.
Despite the development of technological advances, he says there is no evidence that Homo sapiens have become more intelligent in the last 50,000 years.
So nothing much has changed in the last 50 000 years...