Family brains: Like it or not, you've inherited your parents' intelligence

BYLINE: Alison Motluk

YOU can claim to have inherited the family nose without inciting controversy. But the mere mention of inheriting the family brain makes people shift uncomfortably. Say that the grey matter passed down through the generations affects how smart or stupid you are, and you're as good as shunned.

Yet that is precisely what scientists in the US and Finland have found: genes strongly influence how certain parts of our brains develop. And the parts genes affect most are those that govern our cognitive ability. In short, you inherit your IQ. That doesn't mean your intellect is set in stone, says Paul Thompson at the University of California at Los Angeles. But it does mean that your genes set the limits on your intellectual prowess. And, say neuroscientists, this may one day help us target the areas of the brain that respond most to environmental stimuli, where the potential for improvement may be greatest.

Thompson and his team studied 10 pairs of identical and 10 pairs of fraternal twins. Identical twins share the same genes, while fraternal twins share half on average. Because twins usually grow up in a similar environment, any differences between the two sets of twins can safely be put down to their genes.

The team used a medical MRI scanner to study the brains of the volunteers, selected from a Finnish twin registry. All twins were same-sex pairs born between 1940 and 1957. Identical and fraternal pairs were matched for age, gender, handedness, social class and how long they'd lived in the same house.

The researchers found that certain regions of the brain were highly heritable. These included language areas, known as Broca's and Wernicke's areas, and the frontal region, which is one of the areas that plays a huge role in cognition. In identical twins, there was a 95 to 100 per cent correlation in these areas between one twin and the other - they were essentially the same. The frontal structure, says Thompson, appears to be as highly influenced by genes as fingerprints. "It's extraordinary how similar they are," he says.

The finding suggests that environment - the twins' personal experiences, what they learned in life, who they knew - played a negligible role in shaping that part of the brain.

Fraternal twins had very similar Wernicke's area, showing about 60 to 70 per cent correlation. But they were less similar in other areas. You'd expect no correlation in random pairs of people.

Even more interestingly - not only was this grey matter highly heritable, but it affected overall intelligence, too. The volunteers each took a battery of tests that examined 17 separate abilities, including verbal and spatial working memory, attention tasks, verbal knowledge, and motor speed.

These tests home in on what's known as "g", the common element measured by IQ tests. People who do well on one of these tests tend to do well on them all, says Thompson. It's not known exactly what g is, but these new findings suggest that it is not just a statistical abstraction. Rather, they point to a biological substrate for g in the brain, says Robert Plomin, of the Institute of Psychiatry in London.

But Stephen Kosslyn of Harvard University questions whether g should be called intelligence. It picks up on abilities such as being able to figure out how to order things according to rules. "It's the kind of intelligence you need to do well in school," he says. "Not what you need to do well in life."

Kosslyn also says that many genes turn on or off in response to what happens in the environment. This means that learning and experience can indeed boost your intelligence within its predetermined range.

He thinks that the study may eventually help us target education to areas of the brain that are most responsive to environmental stimuli, such as the sensory areas.

More at: Nature Neuroscience online (DOI: 10.1038/nn758)

For more science news see http://www.newscientist.com

LOAD-DATE: November 9, 2001