The Washington PostDemocracy Dies in Darkness

Knowing more about our genes shouldn’t affect how we raise our kids

The limits of genetic determinism.

Scientists examine DNA gel used in genetics, medicine, biology, pharmaceutical research and forensics. (Klaus Ohlenschlaeger /Alamy Stock Photo)

The question has once again surfaced: What matters more — nature or nurture? “Blueprint: How DNA Makes Us Who We Are,” a new book by psychologist Robert Plomin, argues for nature, reassuring parents that they needn’t worry about screwing up their kids because parenting makes little difference.

Plomin weighs in on a very old debate, one that began at least 2,500 years ago in ancient Greece. This age-old conversation, however, serves to reinforce the prejudices of those participating in it, rather than offering any salient advice on how we are supposed to live and act.

In the 5th century B.C., many leading intellectuals grappled with the relationship between “nature” and “nurture.” The Greeks called nature “physis” (from which we get “physics”) and nurture “nomos,” which is more properly translated as law, custom or convention. Naturalists like Hippocrates, the famous doctor, investigated the role of biology and natural environment in making people more or less susceptible to various illnesses. And the Sophists, teachers-for-hire who flocked to Athens, frequently debated whether nomos or physis was supreme.

While some of those who ran in these intellectual circles advocated for the primacy of nomos, without which nothing would restrain human nature, others insisted that physis could not, or should not, be opposed. In the opening lines of Plato’s “Republic,” the Sophist Thrasymachus declares that justice is nothing more than the interest of the stronger. (In recent days, Bret Kavanaugh has been compared to Thrasymachus.)

The historian Herodotus, who spent a great deal of time in Athens while this debate was in full swing, also weighed in. He argued that both environmental and genetic factors (though he, of course, didn’t understand genetics as we do) influence human character and the success or failure of human societies. In his history of the Persian Empire, Herodotus used the interplay between nomos and physis as an explanatory tool for historians, as when he — or his character Cyrus the Great, a Persian king — claimed a link between “soft lands” and “soft men.”

Herodotus made explicit claims about the primacy of nomos over physis in his account of the Spartan stand at Thermopylae in 480 B.C. According to the mythology surrounding the Spartans, they were very concerned with physis. For example, they regularly committed infanticide to ensure that only the fittest children were allowed to live and even engaged in wife-swapping so that the most strapping Spartan man could have children with the most strapping Spartan woman, even if they were married to other people. Yet Herodotus’s Spartans resisted the Persians at Thermopylae not because of their superior biology but because of their unique society.

Herodotus invented a meeting on the eve of the battle between the Persian king Xerxes and the exiled Spartan king Demaratus. In it, the two opponents debate what matters most: being physically hardier or years of training and education. Nature or nurture?

Xerxes admits that his men might be physically inferior to the Spartans, but fear of Xerxes would impel the Persians to fight beyond their nature. Demaratus counters by saying that even though the Spartans, as residents of a harsh land, are naturally well endowed, nomos would be decisive. The Spartan nomos, instilled by years of brutal military education, dictated that a Spartan never yields his place in battle.

Though the Persians eventually won at Thermopylae, they did so only by treachery and after losing myriad soldiers. But Herodotus’s account of Spartans, and his emphasis on their nomos over their physis, is instructive for how we are to respond to the research of Plomin and others.

While the ancient Spartans didn’t have access to a map of their genome, they did believe they were biologically superior. But they fought so well against the Persians because of the training Spartans received as part of their way of life. And even if that way of life was a reflection of their DNA — and somehow they knew that — it wouldn’t have made any practical difference to their commitment to live a certain way.

This lesson from ancient Greece suggests we should reject genetic determinist ideas — or at least question their usefulness. If parenting doesn’t make a difference, or is nothing more than a result of the parents’ own DNA (Plomin seems to make both arguments), a parent’s responsibility to raise their child to the best of their ability changes not a wit — nor do society’s responsibilities to its members, even those with what Plomin would consider a poor genetic endowment.

Of course, many now, as in the past, do think research like Plomin’s should have an impact on public policy. And that has proved troubling for experts like Nathaniel Comfort, a historian of medicine at Johns Hopkins University. Reviewing Plomin’s book in “Nature,” Comfort worries that “people would be defined at birth by their DNA” if Plomin’s argument won the day. And as I’ve discussed here, “race science” is once again growing in popularity — which Plomin’s work will do little to dissuade.

Just as Herodotus’s Spartans would have carried on with business as usual should they have undertaken a modern analysis of their DNA, parents and everyone else should probably still try their best, even for those who might have less of a chance of “success” because of their genes. As Plomin seems to suggest, neither we nor the Spartans would have much of a choice in the matter anyway.