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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鈥檙e 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鈥檛 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鈥檇 lived in the same
house.

The researchers found that certain regions of the brain were highly
heritable. These included language areas, known as Broca鈥檚 and Wernicke鈥檚 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鈥攖hey were essentially the same.
The frontal structure, says Thompson, appears to be as highly influenced by
genes as fingerprints. 鈥淚t鈥檚 extraordinary how similar they are,鈥� he says.

The finding suggests that environment鈥攖he twins鈥� personal experiences,
what they learned in life, who they knew鈥攑layed a negligible role in
shaping that part of the brain.

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

Even more interestingly鈥攏ot 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鈥檚 known as 鈥済鈥�, 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鈥檚 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. 鈥淚t鈥檚 the kind of intelligence you need
to do well in school,鈥� he says. 鈥淣ot what you need to do well in life.鈥�

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.