Is a left-wing author allowed to believe in genetics? The question is only partially sarcastic: Doctrinaire progressives are inclined to cringe (at least for public consumption) at the idea that one’s DNA might drive real differences that shape our lives. Indeed, the whole concept is seen as a means of justifying social inequality, and perhaps even a step down the slippery slope to eugenics.

But there’s been pushback among some progressives recently, based on the idea that anyone who cares about equity or social justice should care about genes. After all, the genes we get are purely a function of luck—an unfair and unequal system of advantages and disadvantages whose effects can be addressed through public policy. In this regard, at least, genes aren’t too different from other forms of “privilege” that progressives talk about all the time.

Last year, the socialist writer Fredrik deBoer floated this sort of argument in The Cult of Smart, a book that was long on provocative ideas, but lacking in scientific explanation. In The Genetic Lottery: How DNA Matters for Social Equality, soon to be published by Princeton University Press, behavioral geneticist Kathryn Paige Harden expertly addresses that shortcoming.

Part of Harden’s task is simply to distance genetic research from some of the policies and ideas with which it’s sometimes been historically associated. She acknowledges and condemns the role that genetic science has played in eugenics, for example, and reiterates her skepticism (prominently aired in a co-authored 2017 Vox article) of the idea that genetic differences are linked to a racial IQ gap. Most importantly, she expertly sets out the current state of genetic research, and argues the philosophical case that what we know about the subject is consistent with an egalitarian worldview. The book feels incomplete, however, when it comes to the question of how society should be restructured to address the inequities linked to the genetic lottery.

The scientific idea that one’s genes affect one’s life outcomes isn’t novel. During the early Cold War period, researchers already were conducting systematic “behavioral genetics” studies on different types of siblings, twins in particular. Identical twins share twice as much genetic material as fraternal twins; so if genes are important, then, other factors being equal, the life outcomes of identical-twin pairs should be more similar than those of fraternal-twin pairs. When you read that a given trait is estimated to be “X percent genetic,” with Y percent attributed to “shared environment,” and Z percent to “unshared environment,” someone is probably citing a twin study.

This work generally has tended toward the conclusion that genes have a strong effect on most traits, though rarely an effect that is all-powerful. However, there are some skeptics, especially on the Left, who dismiss such findings; claiming, for instance, that identical twins’ similarity in life outcomes might originate in their being treated alike precisely because they present to their parents and others as identical, and not because they happen to have the same genes. In the past decade or so, however, behavioral geneticists have moved beyond these traditional experimental designs, and are now more focused on individuals’ actual DNA.

One new technique allows researchers to compare siblings—not just twins, but all full siblings—by reference to the random genetic draw each received from their parents. By chance, some sibling pairs are more genetically similar than others, because their random DNA draws happened to pick up more of the same parental source. (Harden, for example, reports that she shares just 44.6 percent of her genes with her brother, well below the expected average of about 50 percent.)

If sibling pairs that are more genetically similar also tend to have more similar life outcomes, we can be confident that the relationship is one of causation—not mere correlation—because the genetic similarities emerge from a random process. (It’s similar to any randomized scientific experiment, only nature is doing the randomization for us.) In general, this research shows us that the conclusions drawn by researchers in early twin studies were correct. However, the various methods do produce somewhat different estimates of the effect of genes—which Harden depicts in a useful chart summarizing research that’s been conducted in the areas of education, height, age at first birth, and body-mass index. (Heritability estimates for educational attainment, for instance, range from roughly 20 to 40 percent, depending on which research technique one applies.) But the bottom line is that genes really do matter greatly for a wide range of important outcomes. One analytical method, for instance, suggests that genes associated with educational attainment predict one’s adult income level about as well as does one’s parents’ income level. And someone with a high score on this genetic metric is several times as likely to graduate college as someone with a low score.

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But at this point, let’s back up for a moment. As some informed readers may already have noted, the idea that a gene may “cause” this or that trait isn’t as simple as my language might suggest. As Harden explains, genes don’t operate in a vacuum, but instead express themselves within human societies characterized by their own unique biases, technologies, cultural practices, economic structures, and educational systems. To the extent that genes can be said to cause anything, they do so in a way that’s influenced by environmental context.

As sociologist Christopher Jencks once pointed out, in a society that refused to educate redheads, a gene for redheadedness would be seen as a “cause” of illiteracy: If you randomly assigned a child to possess that gene, the child would grow up unable to read. The resulting redhead/brunette gap would be nominally associated with a genetic marker, but the gap would hardly be intractable, because society could fix it by being more equitable to redheads. The wide availability of eyeglasses, a technology that addresses genetic disadvantages associated with bad eyesight, is a non-hypothetical example that shows how the effects of a genetic difference can vary widely based on the societal or technological environment in which that difference is expressed.

So, in thinking through how genetic findings affect social policy, we can’t stop at the conclusion that genes cause some set percentage of outcomes: We need to flesh out how they cause those outcomes, and ask if these processes could reasonably be changed.

As Harden notes, the genes that affect educational attainment are expressed in the brain, begin affecting development early in life, and seem to affect both intelligence and non-cognitive skills. It immediately occurs to the reader that it’s hard to imagine a modern world in which intelligence and non-cognitive skills don’t affect how far one goes in school—though of course we can make life better for people who are born with bad genetic luck in this area, including by improving their education.

Jencks’s cautionary theoretical tale about red hair is instructive, too, because there are plenty of ways in which our genes set in motion positive or negative environmental feedback loops. Harden reports, for instance, that children with genes associated with academic success also tend to get more intellectual stimulation from their parents. Our genes also contribute to how we’re parented more generally, and how attractive we are perceived to be.

Nonetheless, it’s clear that comprehensively addressing the unfairness caused by genes couldn’t be accomplished merely by making everyone less bigoted. In fact, as bigotries and other artificial limitations fall away—i.e., as we come closer to achieving the “equality of opportunity” associated with a free and tolerant society—genes can actually have a more pronounced effect on outcomes, because those with genetic gifts are held back less often. Harden discusses some fascinating studies in this regard. In Estonia, for instance, genes for educational attainment were shown to produce an increased advantage for those children who came of age after the Soviet withdrawal in 1994. The same is true of recent cohorts of American women, who’ve been less constrained by traditional gender roles than were their forebears.

And so, to truly address the unfair social outcomes associated with genes, we’d need to go beyond the usual principles of free-market liberalism, and address the enormous economic dividends paid to those of us who possess highly remunerative skills that have genetic underpinnings. And this brings us to some of the shortcomings of Harden’s book.

Harden is correct that none of us did anything to “earn” our genes; nor, for that matter, the homes into which we were born. As she notes, when you combine the “shared environment” factors with the estimated genetic effects in twin studies, these (unearned) causes explain most of what there is to explain—with the leftover portion comprising a sort of “free will” residual, which serves to illustrate why even identical twins growing up together will end up on (at least somewhat) different paths. That residual figure tends to be around 20 percent or so for educational outcomes, and about twice that for income.

Harden is also right that we can recognize the power of genes without invoking them to justify inequality as a “natural” phenomenon. Genes do explain, to some extent, why some people are more economically productive, and thus earn more than others, given the demands of a modern economy. But, again, genes are just luck. And the structure of the economy is something we can change.

At the micro level, Harden has a lot of useful insights and suggestions. For example, she points out that our policies can either narrow or widen genetic inequalities. Some interventions seem to help people with a genetic predisposition toward obesity, for example; while cigarette taxes seem to help reduce smoking more among people who are not especially at risk genetically, leaving those with the most intractable addictions to pay the price every time they feed their habit. She also urges researchers not to ignore genetics when they study people’s traits and efforts to change them (an argument that many Quillette readers have been familiar with since 2017).

But looking beyond such abstract considerations, a reader is left grappling with the enormous challenge to traditional concepts of “meritocracy” and free-market economics that Harden’s analysis implicitly presents. In this area, I found The Genetic Lottery a bit thin, perhaps because the author’s expertise is rooted in genetics rather than, say, modes of economic redistribution. She outlines the philosophical principles at play nicely, with the requisite hat-tips to John Rawls’s “veil of ignorance,” but doesn’t quite succeed in showing us how a genetically-informed Rawlsian policymaking approach would work in practice.

Harden writes that school curricula can be structured in a way that’s “equity-promoting” or “performance-maximizing.” But it isn’t clear what the best tradeoff between these two goals is. If you focus educational efforts on the lowest-ability students, you might bring everyone up to an important baseline of mathematical and verbal skill. But teaching to the highest-ability students might drive more achievement at the top of our economy, with more inventions and medical breakthroughs that help everyone (including people born in the future, whatever their genes). The tradeoff involves not only raw, utilitarian cost-benefit analysis, but also the question of how much we subjectively value equity for its own sake.

Thinking about this kind of tradeoff leads a reader to larger questions that extend well beyond the classroom. Capitalism pushes us to use our talents for the good of others, if only to be compensated in return. This keeps us busy working, and produces a wellspring of goods, services, and discoveries—but also allows some of us get far richer than others. (Harden acknowledges this “instrumental” value of the market processes that create inequality.) On top of that, of course, many people (Americans in particular) see economic freedom as good in itself. And so modern welfare states seek to harness the productive efficiencies and freedoms associated with capitalism, while also addressing poverty and low social mobility through taxes, transfer payments, regulations, education incentives, and so on (which is why, in almost all developed countries, government spending tends to fall roughly between 40 and 60 percent of GDP). Most forms of policy disagreement in these countries are rooted, in one way or another, in questions relating to how big this social safety net should be and how it should be structured.

Harden clearly thinks the US safety net should be stronger than it is, but her case for this barely rises beyond a sketch. There’s little engagement, for example, with longstanding and complicated academic debates over the roots of American poverty and inequality, including the question of whether generous social programs might create perverse incentives. And so while Harden cites the power of genes and family background as evidence that our understanding of “personal responsibility” is overblown, she doesn’t really get into the weeds of what kind of policy change should follow from this insight.

To be fair to Harden, she set out to write a book that required her to speak as a geneticist, a philosopher, and a policy wonk, and she succeeded quite well on two of three counts. At the very least, she made a much-needed case for the proposition that progressives cannot continue to ignore the reality of human genetics.