Suppose a couple has a strong family history of schizophrenia. They expect their children will be at high risk. They do IVF and get ten embryos. Polygenic screening reveals that nine of the embryos are at high risk for schizophrenia, but one is safe. They implant the safe embryo, and have a healthy child who never develops the disease.

Some commenters challenge my statement that this represents successfully preventing schizophrenia, at least in the same way that eg better prenatal nutrition prevents schizophrenia. They point out that it didn’t exactly prevent schizophrenia in any particular person, so much as replace a schizophrenic with a non-schizophrenic.

I can never tell how much of this is linguistic hair-splitting versus an actual moral objection to considering this strategy a success, but I think it’s worth arguing against the moral objection.

One easy argument: even if this doesn’t prevent schizophrenia on an individual level, it prevents it on a family and social level. The couple gets to have a non-schizophrenic child instead of a schizophrenic one. Society gets a productive taxpayer instead of someone who they might be a net consumer of health care resources. All of this is true, but slightly gross. Medical care helps society, but it shouldn’t primarily be designed to help society; it should be geared at helping individuals.

Still, I think that - even though this is a weird situation - it’s fair to gloss selection as “preventing a case of schizophrenia”, such that we should treat it approximately the same as prevention via improved nutrition or any other intervention. Once again, my thought process centers around avoiding isolated demands for rigor - ie what happens when we try to think of this the same way we think of other clearer examples where everyone already agrees. Here are three situations that I use as intuition pumps for this case:

Situation 1: The Alcoholic

A woman is planning on getting pregnant. She talks this over with her doctor, who asks her some screening questions and discovers she is a heavy drinker. The doctor warns the woman that her child is at risk of fetal alcohol syndrome, and advises her to quit alcohol before becoming pregnant. She goes to a rehab for three months and quits alcohol. Then she becomes pregnant and has a healthy child without fetal alcohol syndrome.

In common language, we would say that the doctor’s intervention prevented the baby from getting fetal alcohol syndrome. But a woman produces ~one egg per month, so the post-rehab egg that produced the healthy baby was different from the egg that would have produced the baby if she’d gotten pregnant right away. They’re different babies! She has, essentially, replaced a baby who would have had fetal alcohol syndrome with another baby who doesn’t have it.

Still, in common language we call this “preventing the baby from having fetal alcohol syndrome”. Nobody thinks there are any ethical ramifications. Nobody thinks this is a creepy case of putting the needs of the mother and society above the needs of the baby. It’s just an obvious unalloyed good thing.

Situation 2: The Intern

A woman goes in for IVF. She produces ten embryos. The usual technique for deciding which of the ten embryos to implant is for a doctor to look them over and see which one looks generally the most normally-shaped and healthiest. This time, the doctor tells the intern to make this decision. The intern chooses embryo #5. But a few hours later the doctor gets nervous, decides to double-check, disagrees with the intern’s assessment, and picks embryo #7. Embryo #7 gets implanted, and the woman gives birth to a healthy child.

I think most people would think of this as a completely normal day in the life of an IVF doctor (which it is), and deny that it had any additional ethical ramifications. It’s true that embryo #5 was briefly destined to be implanted and born and grow into a human being, and that the doctor’s decision caused that not to happen. But almost nobody would consider this an injury done to embryo #5 or consider this to be impermissible meddling in the threads of Fate. Nobody would say that, once the intern had picked #5, it was wrong for the doctor to switch to #7 in the name of health.

Situation 3: The Parenting Workshop

A social reformer is against child abuse. She sponsors workshops with high-risk teenage boys, where she teaches them some parenting skills that will be useful to them after they get married and become fathers. Studies show that these workshops are very effective, and that when these boys grow up, their children get abused much less often then those of equally high-risk boys who didn’t attend the class.

A skeptic pipes up: these boys had to walk to the reformer’s workshop. This very slightly jostled their testicles, which changed the distribution of sperm, which means there’s no way that the exact same spermatozoon fertilized their wives’ eggs as would have fertilized them if they’d never been to the workshop. Therefore, the workshop didn’t prevent abuse in any particular child who would have otherwise been abused. It just caused a different crop of children to be born and not abused.

I think this skeptic is exactly right that sperm production is so stochastic that there’s no way their children had exactly the same genes after the workshop as in the counterfactual world where they didn’t attend. Still, this is an insane way to think about things, right? You just say that the workshop prevented child abuse.

I think the strongest objection to selection would come from someone who is anti-abortion. If they think life begins at conception, then actual harm is done to a frozen embryo if it is not selected (and so probably eliminated).

But even this isn’t an argument against polygenic selection. It’s an argument against IVF in general, which usually involves production of more embryos than the couple intend to bring to term. As in Situation 2, usually the doctor chooses the most robust looking one that they have a good feeling about, and throws away the others. An Alabama court made this argument on anti-abortion grounds recently. But once you’re already doing IVF, selecting the embryos based on some criterion, like low schizophrenia risk, doesn’t make this issue any worse.

And if the anti-abortionist doesn’t have much of a case here, pro-choice people have even less of a case. This is a non-injury to something they don’t even acknowledge as having rights anyway. It maps to cases where everyone agrees a good thing has been done, like asking pregnant women not to drink, or teaching high-risk men parenting skills. We call these “preventing fetal alcohol syndrome” and “preventing child abuse”, and it’s equally fair to call polygenic selection “preventing schizophrenia”.