Genetic correlation between friends

There is an interesting, and sexy, line of research which suggests that people who are non-related friends are genetically more similar than you’d expect. For years people have been telling me privately that this is not likely to be robust, and probably just really really subtle structure (friends of mine). But most of these were private gripes. Now a group has written a preprint outlining the basis from skepticism, No evidence for social genetic effects or genetic similarity among friends beyond that due to population stratification: a reappraisal of Domingue et al (2018):

Using data from 5,500 adolescents from the National Longitudinal Study of Adolescent to Adult Health, Domingue et al. (2018) claimed to show that friends are genetically more similar to one another than randomly selected peers, beyond the confounding effects of population stratification by ancestry. The authors also claimed to show ‘social-genetic’ effects, whereby individuals’ educational attainment (EA) is influenced by their friends’ genes. Neither claim is justified by the data. Mathematically we show that 1) although similarity at causal variants is expected under assortment, the genome-wide relationship between friends (and similarly between mates) is extremely small (an effect that could be explained by subtle population stratification) and 2) significant association between individuals’ EA and their friends’ polygenic score for EA is expected under homophily with no socio-genetic effects.

Almost no one is a genetic determinist except in your Communist imagination

Next summer I’m going to be giving a talk at the ISIR meeting. I’m a little bemused about this since, to be honest, I don’t talk much about behavior genetics and intelligence anymore.

Until August of 1998, I had rather conventional views for someone of my education and social background on psychometrics. Then I read Chris Chabris’ article in Commentary. From that, I began to conclude the “orthodoxy” that was presented in the elite media really wasn’t representative of what was going on in the field of psychometrics. It’s kind of like thinking that you get a balanced view of the Arab-Israeli conflict from reading Commentary.

Over the next few years, I read some books, review papers, and updated my views. Every few years I read a book or checked out a paper to see if anything had changed…and usually not to my eye as someone who is not in the field. About a decade ago I read What Is Intelligence?: Beyond the Flynn Effect. More recently I read Stuart Ritchie’s Intelligence and Richard Haier’s The Neuroscience of Intelligence. And other things here and there.

I’ll be reviewing Blueprint: How DNA Makes Us Who We Are, but I do wonder if it’s nothing more than an incremental improvement upon The Nurture Assumption: Why Children Turn Out the Way They Do.

Incrementalism isn’t a problem. I am a big fan of genomics. But its impact has been variable. And frankly in some fields less than you might think. I don’t believe it has changed our understanding of evolutionary process qualitatively (rather, it has allowed a finer-grained resolution to certain arguments around particular hypotheses). Educational attainment 3 is great. But does it change how heritable I think intelligence is in a qualitative sense? Not really. We already knew it was a heritable trait, and we’ve known it for a long time.

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Applying intelligence to genes for intelligence

Carl Zimmer has an excellent write up on the new new Nature study of the variants associated with IQ, In ‘Enormous Success,’ Scientists Tie 52 Genes to Human Intelligence.

The issue with intelligence is that it’s a highly polygenic trait for which measurement is not always trivial. You need really large sample sizes. It’s about ten times less tractable than height as a quantitative trait. There are still many arguments about its genetic nature (though a majority position that it’s not rare variants of large effect seems to be emerging).

But all in good time.

Science is divided into many different fiefdoms, and people don’t always talk to each other. For example I know a fair number of population genomicists, and I know behavior geneticists who utilize quantitative genomic methods. The two are distinct and disparate groups. But the logic of cheap sequencing and big data is impacting both fields.

Unfortunately when you talk to population genomicists many are not familiar much with psychology, let alone psychometrics. When it comes to the behavior geneticists many come out of psychology backgrounds, so they are not conversant in aspects of genetic theory which harbor no utility for their tasks at hand. This leads to all sorts of problems, especially when journalists go to get comments from researchers who are really opining out of domain.

Some writers, such as Carl Zimmer, are very punctilious about the details. Getting things right. But we have to be cautious, because many journalists prefer a truth-themed story to the truth retold in a story format. And, some journalists are basically propagandists.

Over the next five years you will see many “gene and IQ” studies come out, with progressively greater and greater power. Read the write-ups in The New York TimesScience, and Nature. But to my many readers with technical skills this is what you should really do:

  1. pull down the data.
  2. re-analyze it.

My plain words are this: do not trust, and always verify.

I’m a big fan of people educating themselves on topics which they have opinions on (see: population genetics). If intelligence is of some interest to you, you should read some things. Arthur Jensen’s classic The g Factor: The Science of Mental Ability can be quite spendy (though used copies less so). But Stuart Ritchie’s Intelligence: All That Matters and Richard Haier’s The Neuroscience of Intelligence are both good, and cheaper and shorter. They hit all the basics which educated people should know if they want to talk about the topic of intelligence in an analytical way.