In 2020, a company called Genomic Prediction started offering genomic scores for diabetes, skin cancer, high blood pressure, elevated cholesterol, intellectual disability, and “idiopathic short stature.” They’ve stopped advertising the last two “because it’s too controversial.” Not, mind you, because the effects are minor and the science is unreliable. The theoretical maximum polygenic score for height would make a difference of 2.5 inches, and that theoretical maximum has not been seen yet, even in studies of Europeans. Polygenic scores for most other traits lag far behind. (And that’s just one company; another called Herasight has since picked up the slack and claims to offer embryo selection based on intelligence.)

Remember, the more traits one selects for, the less accurate each prediction is. Moreover, many genes affect multiple biological processes, so a gene implicated in one undesirable trait may have as yet undefined impacts on other desirable ones.

And all of this is ignoring the potential impact of the child’s environment. The first couple who used genetic screening for their daughter opted for an embryo that had a reduced risk of developing heart disease; her risk was less than 1 percent lower than the three embryos they rejected. Feeding her vegetables and sticking her on a soccer team would have been cheaper and probably more impactful.

The risks of reduced genetic diversity

Almost every family I know has a kid who has taken growth hormones, and plenty of them get tutoring, too. These interventions are hardly equitably distributed. But if embryos are selected based on polygenic scores, the authors fear that a new form of social inequality can arise. While growth hormone injections affect only one individual, embryonic selection based on polygenic scores affects all of that embryo’s descendants going forward. So the chosen embryos’ progeny could eventually end up treated as a new class of optimized people whose status might be elevated simply because their parents could afford to comb through their embryonic genomes—regardless of whether their “genetic” capabilities are actually significantly different from everyone else’s.