Genetics guide to man's IQ

CLEAR evidence that intelligence is largely determined before birth has emerged from a genetic study of twins.

The findings showed genetic factors accounted for differences between individuals in key areas such as intelligence and language ability. Grey matter volume -- a measure of the brain cells' density -- was strongly determined by genes and reflected cognitive performance.

Researchers led by Dr Paul Thompson, of the University of California at Los Angeles, compared 20 twin pairs, half of whom were identical and half non-identical.

Identical twins have the same genes, whereas non-identical twins, like ordinary siblings, share about half.

Features which are the same in identical, but not non-identical twins, are therefore likely to be governed by genetic factors. New 3D imaging techniques enabled the scientists to look for subtle similarities and differences in brain structure.

There are thought to be strong genetic influences on IQ, verbal and spatial abilities, perceptual speed and even some personality traits, including emotional reactions to stress.

The California findings were reported in the journal Nature Neuroscience. The researchers wrote: "The resulting genetic brain maps reveal a strong relationship between genes, brain structure and behaviour, suggesting that highly heritable aspects of brain structure may be fundamental in determining individual differences in cognition."

LOAD-DATE: November 4, 2001