Where is the heritability of intelligence hidden in our genes?

I’m quite sure that the title of this post may have upset some people already. The reason is that both heritability and intelligence can be regarded as problematic concepts by even researchers. Still, bear with me, because this new study is quite intriguing.

The following key points actually describe a steep evolution in our knowledge about both the genetic and heritability components of our intelligence (which aren’t synonyms to be clear):

  • Until 2017, genome-wide polygenic scores derived from genome-wide association studies (GWAS) of intelligence were able to predict only 1% of the variance in intelligence in independent samples.
  • Polygenic scores derived from GWAS of intelligence can now predict 4% of the variance in intelligence.
  • More than 10% of the variance in intelligence can be predicted by multipolygenic scores derived from GWAS of both intelligence and years of education. This accounts for more than 20% of the 50% heritability of intelligence.
  • Polygenic scores are unique predictors in two ways. First, they predict psychological and behavioural outcomes just as well from birth as later in life. Second, polygenic scores are causal predictors in the sense that nothing in our brains, behaviour or environment can change the differences in DNA sequence that we inherited from our parents.
  • Polygenic scores for intelligence can bring the powerful construct of intelligence to any research in the life sciences without having to assess intelligence through the use of tests.

The key element in this paper is the concept of polygenic scores. What are they?

A polygenic score, also called a polygenic risk score, genetic risk score, or genome-wide score, is a number based on variation in multiple genetic loci and their associated weights (see regression analysis). It serves as the best prediction for the trait that can be made when taking into account variation in multiple genetic variants. (wikipedia)

My attempt to say it as easy as possible: intelligence isn’t located on one gene, but is due to the combination of a lot of genes.

Now the good thing and the thing that even frightened me. First the good thing: Plomin and von Stumm don’t say everything is down to our genes. That would be downright stupid, btw. That is why the last key point frightens me as it makes everything much too deterministic and limits intelligence to something purely native. Also, if I read the article correctly, there is still a long way to go.

Although the authors do go into the ethical side of their work, this element is not really discussed. Did I mention I think this paper is intriguing?

Abstract of the article in Nature:

Intelligence — the ability to learn, reason and solve problems — is at the forefront of behavioural genetic research. Intelligence is highly heritable and predicts important educational, occupational and health outcomes better than any other trait. Recent genome-wide association studies have successfully identified inherited genome sequence differences that account for 20% of the 50% heritability of intelligence. These findings open new avenues for research into the causes and consequences of intelligence using genome-wide polygenic scores that aggregate the effects of thousands of genetic variants.

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