Do genes determine intelligence? Both conservatives and liberals are ignoring the realities of biology

To a large extent, I expected this, as I know the author personally. We both live in Austin, where she is a professor at the University of Texas. I became acquainted with Harden in 2016 following a massive social media conflagration triggered by her sensible contention that liberals needed to acknowledge the insights of behaviour genetics, and that the field was not necessarily racist.

A committed band of online “social justice warriors” have continued to hound her; a population geneticist told me several years ago that another scientist at a seminar dismissed Harden as “Charles Murray in a skirt”. This was somewhat ironic given that she once wrote a piece titled “Charles Murray is once again peddling junk science about race and IQ”. Harden’s disagreements with conservatives also elicit outrage from the online Right, but that is of little impact. As an academic, the only serious reputational risk comes from the baying of her own ideological tribe.

It’s unfortunate, then, that though Harden provides a potted history of eugenics, much of her historical interpretation is tendentious, and seems geared to reassuring the intended audience that they are on the right side of history. She observes, for instance, that the statistician and eugenicist Karl Pearson “argued that progressive-era social reforms, like the expansion of education, were useless”. What the reader may fail to glean from this is that Pearson was a committed socialist and freethinker, who was also engaged with feminism and suffrage.

Where the narrative shines is when Harden explores fields that have long been taboo. For example, the notion that genetics can cause patterns in social phenomena is ignored by whole fields of scholarship, but it’s no coincidence that adopted individuals are much more likely to engage in crime as adults if their biological parents were convicted of offences.

Harden further illustrates this with her own research on abstinence from sex. The State of Texas promotes abstinence policies because it believes there is a strong correlation between early sexual activity and negative life outcomes such as crime. To test this assumption, Harden’s team tracked down identical twins, who share both genes and environment, and first had sex at different stages in life. They found that there was no difference in life outcomes.

The Genetic Lottery comes alive whenever Harden writes about her own research. At one point, she reports that “executive function” — your cognitive behaviour, ranging from memory to self-control — is nearly 100% heritable in children, meaning that all the variation in the population can be attributed to variation in genes. The correlation in executive function between identical twins is 1.0, while between full siblings it is 0.5. Since twins share 100% of their genes and full-siblings just 50%, this is exactly the pattern you would expect in a fully heritable characteristic, whether executive function or eye-colour. This research has no straightforward immediate political implications, so the exposition is freed from a need to gauge the impact on the audience.

But statistical correlations remain unconvincing to many. A specific criticism of twin-studies centres on the likelihood that parents treat twins more similarly than full-siblings. That’s partly why the late population geneticist Richard Lewontin thought behaviour genetics was a useless field with deep methodological problems. His views are not unusual for geneticists who work in molecular or evolutionary (rather than behavioural) fields today.

It is at this point that Harden illustrates why her book could only be written in 2021. Whereas past geneticists had to assume that full-siblings were exactly 50% related, today genomics allows a precise quantification of the level of relatedness. I know, for instance, that I share 52.49% of my DNA with one brother, 50.26% with another, and 4.57% with my first-cousin once-removed (the expectation in the last case is 6.25%).

In 2006, geneticists applied the new technology to the study of heritability, generating relatedness scores from genomics for thousands of sibling pairs. They discovered that very heritable traits did indeed show more similarity in those siblings who were genomically more related. Heritability was more than a statistical construct, it was a biophysical reality.

One of the most striking figures in The Genetic Lottery shows that “polygenic risk scores”, a statistic used to predict your position along a distribution of values, such as from shortest to tallest, are already as powerful as parental income at predicting the rate of college completion. Those students in the bottom 25% of parental income have a 15% chance of completing college. Those in the bottom 25% of the polygenic risk score also have a 15% chance of doing so.

This task in explaining the state of behaviour genetics today is helped by bodies such as the UK Biobank, which offers researchers 500,000 individuals with 820,000 genetic markers per individual. It has resulted in papers which are generated in an almost turnkey fashion. Consider “Genetic correlates of social stratification in Great Britain”, which concludes that “Alleles associated with educational attainment (EA) showed the most clustering, with EA-decreasing alleles clustering in lower SES areas such as coal mining areas”. In plainer English, smarter people migrated south, leaving those remaining in the north of England on average less intelligent due to their genes. Needless to say, this was a controversial result.

Harden spends a great deal of time exploring population structure because of its relevance to possible variation in human psychology and behaviour. She reports on survey data that liberals in particular are suspicious of — results which indicate variation in intelligence due to genes — and she argues that this is due to its connection with the history of racism and classism in the United States. Harden asserts that intelligence is heritable within a group, but does not necessarily imply that it explains differences between groups in outcome.

The targeted readership for The Genetic Lottery will almost certainly dismiss the case for behaviour genetics if that requires them to connect it to potentially racist implications. Yet Harden’s book is actually rooted in social justice, and her belief that “people’s moral commitments to racial equality are on shaky ground if they depend on exact genetic sameness across human populations”. Nevertheless, much of the narrative gets bogged down in race and particularities of American politics.

Harden is a white liberal who is deeply committed to the cause of racial justice in the historical context of black and white Americans. Presumably her audience is as well. But her ultimate goal is to talk more about John Rawls than Ibram X. Kendi. For The Genetic Lottery is a theory of justice informed by unearned genetic advantages and undeserved genetic disadvantages.

Harden personalises this by contrasting herself with her brother. Though siblings are 50% similar, she explains, they are also 50% different. Raised in the same household, she asks who was dealt the better hand — she did better at standardised tests but also has ADHD — between the two siblings. Do these differences speak at all to the moral value of the siblings? Of course not. We know this intuitively. It is self-evident.

In A Theory of Justice, Rawls introduced the “difference principle”. This argues that inequality in outcomes is permissible if those inequalities benefit the least-advantaged members of society. Similarly, towards the end of her book, Harden considers three scenarios conditioned on Rawls’ “veil of ignorance”, where you don’t know what endowments you’ll randomly be allotted. First, a society where the “biologically superior are entitled to greater freedoms and resources”. Second, a society “structured as if everyone is exactly the same in their biology”. Finally, a society “structured to work to the advantage of people who were least advantaged in the genetic lottery”.

Science does not tell you which choice to select. Harden points out that in the US, both conservatives and liberals often behave as if we live in the second scenario. But what if we consider the reality that outcomes are to some extent caused by varying genes? Though these facts do not necessarily change one’s values, they do change the prescription for how one can achieve the just outcomes we might have in mind.

Of course, biology is not everything, but The Genetic Lottery reminds us that it is a factor we ignore at our own peril when we craft social policy. In 2021, we now have the technology to plumb the depths of our human nature. The results may not always be to our liking, but the facts are ultimately unchangeable.