Is Intelligence in the Genes?

Tom Bartlett, Chronicle of Higher Education, December 21, 2011

At least a dozen papers have been published that appear to show links between general intelligence and specific genes. But the authors of a forthcoming paper, to be published in Psychological Science, contend that those findings are all most likely false. I asked one of those authors, Christopher Chabris, who co-wrote the best-seller The Invisible Gorilla, a few questions via e-mail, and he was kind enough to answer:

So general intelligence is to some degree heritable, but previous attempts to pin down the particular genetic variants involved were flawed because their sample sizes were too small. Is that right?

This is pretty much correct. But I wouldn’t call those studies “flawed” in the sense of “designed erroneously.” When researchers started looking for the genes that contribute to differences in cognitive ability, it was thought, or at least hoped, that there would be specific genetic variants that each accounted for a meaningful portion of those differences, say one to two IQ points. It was also very expensive to assay genes, making it impractical to collect really large samples. So samples were used that in retrospect, given what we now know about the genetics of attributes like height and obesity, seem much too small, and when samples are too small, some of the positive results that turn up are more likely to be accidents than true successful finds. Our article shows that out of the 12 published genetic associations with intelligence that we were able to examine, none consistently replicated in our three samples that totaled almost 10,000 people. This doesn’t mean at all that there are no genes associated with intelligence. It just means that we haven’t found them yet, and this is probably because the common genetic variants that have been studied each have at most tiny effects on intelligence—not the large effects that had been expected when the enterprise of finding those genes began.

This seems like bad news. Does your study mean that, when it comes to figuring out which genes are associated with intelligence, we actually didn’t know what we thought we knew, and now we’re back to square one?

Not at all. We know more about what’s called the “genetic architecture” of intelligence. It turns out to be similar to that of height, which is interesting, since height is a trait that’s easy to measure accurately, not based on mental performance, and not very controversial. For both height and intelligence we now know that there are probably no individual genetic variants that are both common in the population (as opposed to rare mutations that are peculiar to particular families) and responsible for large differences between people in the trait. The field has to look for more genes, each with much smaller effects, which requires different methods from the ones that have been mostly used to date. So we have replaced some conclusions that turned out to be premature with some knowledge that can form a basis for the next steps in working out the genetics of cognitive abilities. I think we have also gained an instructive example of how the scientific literature can wind up—through no one’s fault—incorporating results that turn out to be unlikely to be correct.

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  • Anonymous

    Sorry, but it either is or it is not.  It appears that it is attributable to genes, but there’s enough reasonable doubt to allow this guy to wriggle out of making a definitive statement and ending his career.

    If the “genetic architecture” is very similar to those that control height, and height doesn’t seem to be affected very much by such things as poverty, violence, and “historical disadvantage,” I think the answer to the question of whether or not genes determine intelligence is fairly obvious.

  • Back when I was in school I was taught that genes sets the limits of our intelligence and our environment determines how far we go in reaching those limits.

  • Sherman Ackerson

    The more you study genes, phenotype,  and behavior, the more apparent it is that our genes not only determine our intelligence, but are also responsible for creating our environment.  Every person will eventually create the environment he wishes or deserves, whether a barren room with a couch, Cheetos and a flat screen television or a room with a desk and filled with books.

    • It doesn’t matter much if meth or crack is the neighborhood drug of choice. It doesn’t matter much if you live in a trashy trailer park or a run down ghetto. It doesn’t matter what color your skin, if you have half a dozen sibling by different fathers. The bottom line is, it is hard to create a good environment if you never lived in one.

      • Sherman Ackerson

        Yes, Yes and Yes.  It doesn’t matter.  And if it did, we wouldn’t have Jack London, George Wald, Abe Lincoln, Andrew Carnegie, Oprah Winfrey or millions of others who overcame a bad childhood environment.

        Read Steve Pinker’s The Blank Slate and The Nurture Assumption by Judy Harris to get a refreshing new perspective.  A good environment makes it easier to succeed but in the end we will settle on the environment that best suits our true personality.

  • Andy

    “to some degree”….Ever since the 1988 publicaton of the seminal research survey by Synderman and Rothman, the question marks have been removed as to whether the influence of genes is other than equal to that of nurture–to make a crudely useful distinction between nature and nurture.  The better estimate for heritability of “g” for the U.S. population  is about 80.   The incessant drum beat that we don’t quite know enough to challenge the policies based on Blank Slate mythology is the cadence to a lemming march.    Part of the mass delusion arises from the increasingly contrived “bubble world” nature of American life.   When a large proportion of our population lived on farms or in rural villages,  the observance of the actions and heritability of dogs and horses   (and farm families of 8-10 siblings )  left little doubt as to the impact of genes.  

  • Andy Summer

    Many reports from Africa during its colonization and soon afterward, noted very
    distinct differences in intelligence (as assessed by keen observers and as manifested
    in dwellings, adornment, tribal customs, etc. )  among varied groups of native Africans.

  • acc

    When comparing Eg. a mouse and a human being differences in their IQ may be detected. Both life forms have genes and they are even related.  I dare to present a hypotheses that IQ and genes have a connection.