Genes have a very strong influence over how certain parts of our
brains develop, scientists in the US and Finland have found. And the parts most influenced
are those that govern our cognitive ability. In short, you inherit your IQ.
Thompson at the University of California at Los Angeles and his colleagues used MRI to
scan the brains of 10 pairs of identical and 10 pairs of fraternal twins. Identical twins
have identical genes, whereas fraternal twins sharing on average half their genes. The
twins shared environments, means researchers can separate genetic and environmental
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, among other things, plays a huge role in cognition.
In identical twins, these areas showed a 95 to 100 per cent correlation 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 the most highly influenced trait
we know of - fingerprints.
"It's extraordinary how similar they are," he says. The finding suggests
that environment - their own personal experiences, what they learned in life, who they
knew - played a negligible role in shaping it.
Fraternal twins were near-identical in Wernicke's area, showing about 60 to 70 per
cent correlation, but were less similar in other areas, . Random pairs of people would be
expected to have no correlation.
The study was all the more interesting in that it found that not only was this
gray matter highly heritable, but it affected overall intelligence as well. "We found
that differences in frontal gray matter were significantly linked with differences in
intellectual function," the authors write.
The volunteers each took a battery of tests that examined 17 separate abilities,
including verbal and spatial working memory, attention tasks, verbal knowledge, motor
speed and visuospatial ability.
These tests hone 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
It is not known what exactly "g" is. But these new findings suggest that
"g" is not just a statistical abstraction, but rather, that it has a biological
substrate in the brain, says Robert Plomin, of the Institute of Psychiatry in London.
Plomin has spent eight years looking for genes behind "g". "I'm convinced
that there are genes," he says, a lot of them, each with a small effect.
Stephen Kosslyn of Harvard University in Boston questions whether "g"
should really be called intelligence. "G" picks up on abilities such as being
able to abstract rules or 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."
Journal reference: Nature Neuroscience (DOI: 10.1038/nn758)