One suggested approach is to only implant “intelligent” human embryos and discard the rest, to
avoid editing individual genes:
First, there are obvious problems like, how much is genetics and how much is environment? From MedLine: “Studies have not conclusively identified any genes that have major roles in differences in intelligence. It is likely that a large number of genes are involved, each of which makes only a small contribution to a person’s intelligence… A person’s environment and genes influence each other, and it can be challenging to tease apart the effects of the environment from those of genetics.” Recent genetic studies point to some genes but provide no clear guidance.
It gets more complex. The interaction between genetics and environment plays a big role in intelligence: “… the right question is not a question of Genes v. Environment, the right question is how do genes and environment interact to shape behavior?” (Psychology Today)
And then there’s the Flynn effect: “… people living in the United States were gaining a little more than 3 points per decade on tests of human intelligence.” James Flynn (1934–2020) attributed this effect to the greater opportunity that modern societies offer for abstract, problem-solving approaches to life…
From available knowledge, intelligence boost proposals have all the makings of either nothing or the next ethical train wreck.News, “Could we really increase human IQ via genetic engineering?” at Mind Matters News (August 4, 2022)
Takehome: It’s not clear what, explicitly, human intelligence is or even how it originates. Ethics aside, there’s no way to decide who to save and who to throw away.
You may also wish to read: Can science really engineer a bigger human brain? Computational neuroscientist Daniel Graham wonders why we would bother. There is no strict relationship between brain size and intellectual achievement. The human brain has actually been shrinking in the last 30,000 years, the same period that has also shown great intellectual achievements.