Anytime discussion of a genetic basis behind intelligence comes up we immediately enter a minefield of social and ethical controversies. What actually constitutes "intelligence" in the first place, and what are the practical outcomes of being able to pinpoint so-called "smart" genes? Could we create designer babies with super high IQs, or develop pills that turn on intelligence genes giving us a temporary smart boost?

A giant meta-study comprised of over 78,000 people has confidently identified 52 genes that scientists consider to be significantly associated with intelligence. While only constituting a fraction of the thousands of genes potentially associated with influencing intelligence, this discovery sets scientists on a fascinating path to understanding the genetic roots of intelligence.

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There has long been argument over the degree of heritability of intelligence. A variety of studies have fascinatingly, and counter-intuitively, concluded that genetic influences on intelligence actually increase with age. Dubbed "The Wilson Effect," it has been found that environmental factors dominate intelligence in early years with genetic factors having as little as 20 percent influence in infancy, growing over adolescence to a peak of up to 80 percent in one's early twenties.

This dramatic weighting of nature over nurture in adulthood has been the source of some debate, but even oppositional scientists have generally assumed that the heritable basis of intelligence is not much less than 50 percent. If we could discover which genes are associated with intelligence then we could gain a significant understanding into how our brains function.

An international team of scientists led by Professor Danielle Posthuma, Principal Investigator of the study from VU University in Amsterdam, has made a significant breakthrough identifying 40 previously undiscovered genes associated with intelligence, alongside another 12 that were previously known.

"The genes we detect are involved in the regulation of cell development, and are specifically important in synapse formation, axon guidance and neuronal differentiation," said Professor Posthuma. "These findings for the first time provide clear clues towards the underlying biological mechanisms of intelligence."

The team used a measure of intelligence called "g-factor" to evaluate all the participants in the study. After carrying out a large associational study they identified several hundred SNPs, or single-nucleotide polymorphisms. These are DNA markers that point to a person's likelihood in developing a certain trait, in this case intelligence. After more work they eventually focused in on the 52 specific genes that correlated across the highest intelligence brackets in the study.

The team is careful in making it clear this is only a very small part of the bigger puzzle that makes up an individual's overall intelligence. And even though the "g-factor" is one of the better ways we have to understand intelligence it still doesn't cover the broad variety of intelligences out there, from musical prodigies to those with high "emotional" intelligence.

"The current genetic results explain up to 5 percent of the total variance in intelligence," says Professor Posthuma. "Although this is quite a large amount of variance for a trait as intelligence, there is still a long road to go: given the high heritability of intelligence, many more genetic effects are expected to be important, and these can only be detected in even larger samples."

The team will now move on to specific mouse studies targeting these genes to better understand their broader biological effects, while also attempting to discover even more genes that are part of the larger intelligence puzzle.

The study was published in the journal Nature Genetics.

Source: VRIJE University Amsterdam via Eurekalert