Wikipedia:Reference desk/Archives/Science/2023 October 23

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October 23

Heritability and Intelligence?

Is it possible to predict the intelligence of a child based on the intelligence of its parents? 2A02:8071:60A0:92E0:F0DC:D8BC:3C8D:36F2 (talk) 21:40, 23 October 2023 (UTC)

see Intelligence quotient#Genetics and environment where it mentions to what extent this can be done. Graeme Bartlett (talk) 21:57, 23 October 2023 (UTC)

See also more specifically Heritability of IQ. But note also that intelligence is not necessarily what is measured by IQ.  --Lambiam 09:54, 24 October 2023 (UTC)

The answer also depends on what you mean by "heritable." Technically, heritability of traits doesn't necessarily have to be genetic. For example, the religion of a child is generally the same as the parents, especially if the parents are both of the same religion, thus making it a "heritable trait" that has zero genetic basis. The same can apply to intelligence, to the extent that it can be quantitatively or qualitatively measured. For example, if a child is raised in a home with parents that read a lot of books, those parents will often encourage their child to read, thus passing on "book smarts." Families with generational wealth will often live in communities that have better performing schools, or send their children to better performing private schools, thus adding a socio-economic dimension to "heritability." --OuroborosCobra (talk) 07:49, 24 October 2023 (UTC)

Can someone's religion be called a "trait"?  --Lambiam 09:45, 24 October 2023 (UTC)

Sure. It may be more mutable than many others, and it may not be caused by alleles, but not all traits are fixed and not all traits are genetic. —OuroborosCobra (talk) 15:46, 24 October 2023 (UTC)

Yes, the present evidence is that "nurture" totally swamps out any potential contribution from "nature". All the genome-wide association studies that have been done find very little, if any, genetics for intelligence. Abductive (reasoning) 08:05, 24 October 2023 (UTC)

Citation needed.  --Lambiam 09:47, 24 October 2023 (UTC)

Yeah, I have a feeling that it’s more that we have not necessarily found a genetic link genetic variation within human populations that correlates with differences in intelligence, though this is made difficult by the issue of actually being able to measure intelligence. Obviously there are genetic links to human intelligence vs other organisms, but the that’s a huge difference than the variation within the human population. i.e. you and I both are not sponges and have a genuine, organized central nervous system, but the genetic variation between you and me may not have an identified correlation with our respective intelligence (which, of course, hasn’t even been qualitatively measured). —OuroborosCobra (talk) 15:51, 24 October 2023 (UTC)

I agree that Abductive's statement is misleading. Studies have consistently shown that IQ (yes, not the same as intelligence!) has a heritability of about 0.75 in western populations. That figure factors out the effect of shared family environment: like it or not, it really is genetic variation that explains most of the variation in IQ. But it is true that it is proving difficult to identify particular genes that are responsible for this pattern. Once whole-genome sequencing became routine, this has turned out to be a finding common to many other traits, and the result caught scientists by surprise. My understanding is that the phenomenon is not fully understood, but one hypothesis is that there is variation in lots of genes of small effect that have an influence. JMCHutchinson (talk) 17:29, 24 October 2023 (UTC)

No, it turns out that all those studies were garbage. For example, the "heritability" of IQ varies radically depending on the ages of the people tested, even the same people tested over time. Abductive (reasoning) 18:13, 24 October 2023 (UTC)

Please provide a review in a peer-reviewed genetics journal concluding that these studies are garbage: it is not my reading of the literature. For instance here is a review from 2013 reporting a heritability of 0.8 for IQ in adults. This article also deals with increase of heritability of IQ with age during childhood, which is what one might expect rather than a finding that invalidates earlier studies. Remember that heritability is the proportion of total variation explained by genetics. So in a more variable environment heritability is liable to be lower even if the genetic influences are the same on an absolute scale. Because children mature at different rates (for a diversity of reasons), genetics has relatively less influence on IQ amongst children of the same age than amongst adults. Heritability stabilises at the age of about 20 when everybody has "grown up". It reduces again in old age because then diseases increase the environmental influence. JMCHutchinson (talk) 20:27, 24 October 2023 (UTC)

It's less that the studies were garbage, than that the specific understanding of 'heritability' has generally not been understood fully, and therefore garbage conclusions have been freely reached from the studies. Remsense聊 20:30, 24 October 2023 (UTC)

No genes found the harder they look, heritability itself is a flawed measure that has been largely deprecated, and it varies depending on anything you can name. Yep, garbage. Here, look at this genome-wide association study that purports to find a connection between genetics and school achievement as measured by English, Danish, and Mathematics grades. Abductive (reasoning) 21:05, 24 October 2023 (UTC)

I am puzzled what point you want to make by citing that study. It did find that variation at some particular genetic loci correlated significantly with performance at school, and it thereby estimated heritablity values for various aspects of school performance (e.g. one was estimated to have a heritability of 0.29). Heritability is still widely used by geneticists. JMCHutchinson (talk) 21:44, 24 October 2023 (UTC)

The usual definition of heredity refers only to some twins and is carried out there.

What do you have in the mind.

Interesting discussion. 2A02:8071:60A0:92E0:7CBD:1250:7548:A338 (talk) 21:50, 24 October 2023 (UTC)

It seems to me that Abductive is requiring there to be a very few intelligence gences for heritability to be anything but garbage. However even for things like speed at running or height the case is many genes contribute. Intelligence probably is like speed at running where a large number of genes all have to work together and the effect is multiplicative rather than additive. If anything it is a wonder that there are so few complete idiots - each gene must only have a small range in its effect. NadVolum (talk) 23:54, 29 October 2023 (UTC)