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.
Paul 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 factors.
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, among other things, plays a huge role in cognition.
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In identical twins, these areas showed a 95 to 100 per cent correlation between one twin and the other 鈥� 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 鈥� fingerprints.
鈥淚t鈥檚 extraordinary how similar they are,鈥� he says. The finding suggests that environment 鈥� their own personal experiences, what they learned in life, who they knew 鈥� played a negligible role in shaping it.
Fraternal twins were near-identical in Wernicke鈥檚 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.
Intellectual function
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. 鈥淲e found that differences in frontal gray matter were significantly linked with differences in intellectual function,鈥� 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 is not known what exactly 鈥済鈥� is. But these new findings suggest that 鈥済鈥� 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 鈥済鈥�. 鈥淚鈥檓 convinced that there are genes,鈥� he says, a lot of them, each with a small effect.
Stephen Kosslyn of Harvard University in Boston questions whether 鈥済鈥� should really be called intelligence. 鈥淕鈥� picks up on abilities such as being able to abstract rules or 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�
Journal reference: Nature Neuroscience (DOI: 10.1038/nn758)
