> 18 years

Why 18 years? You can harvest fertile gametes much earlier than that in an ordinary person. And with some unethical drugs you can reduce that age even more.

Just watch out you don't end up selecting for early maturation :)

> Everything I'm reading is saying the genes for IQ, as with most traits, are additive. And it really is as easy as putting as many high-IQ-associated genes into one genome as possible.

High IQ's come with large tradeoffs. Foremost among them is a much higher rate of depression. Second among them is a reduction in socialization.

Bear in mind that that each of the "high-IQ-associated genes" (alleles) is responsible for the synthesis of a polypeptide, and that the phenotypes produced by their interactions can be extremely difficult to predict.

I believe the studies you have in mind, one of which appeared on HN last week, find that high IQ is not associated with any small set of highly unusual alleles (i.e. "freak mutations"). This isn't to say that genetically engineering a person to have a high IQ is as simple as "putting as many high-IQ-associated genes into one genome as possible." It could be the case that certain specific interactions between the products of these alleles prove deleterious to the individual with respect to intelligence or other traits.

I agree that some of the sentiment on HN about the mutability of intelligence is wishful thinking, but our understanding of genomics and the genetic component of intelligence is still very much incomplete.