I see many posts here asking about the genetics of intelligence. Here is the best review to date (it is open access) [1]. The authors have been studying the genetics of intelligence for over 30 years. The tl;dr is that we know if no single genetic switch that can increase intelligence, there seem to be many little switches that give rise to the normal IQ distribution.
As I commented on this interesting article when it was a submission to Hacker News, "Robert Plomin and Ian Deary are mainstream researchers on the behavior genetics of human intelligence, the authors of well regarded textbooks (Plomin), popular books (both), and primary research articles (both) on various related topics. Their joint point of view as expressed in the review article published today is not the exact point of view of all researchers in the field, but I thought it would do as a discussion-starter here on Hacker News.
"A crucial detail (Deary and Plomin would both agree about this, but it hasn't come up in the discussion here yet) is that heritablity has NOTHING to do with modifiability. It is quite possible in principle that a novel environmental intervention might be discovered that could boost most people's intelligence. It is even possible that the most effective intervention might have a gene-environment (G × E) interaction such that the intervention would most help people with lowest IQ, and least help people who already have high IQs. No such intervention that human beings can direct purposefully has yet been found, but it is clear from the Flynn effect[1] that something in the environment can have powerful effects in raising average IQ levels of whole countries, as has happened in the developed world throughout the last century (for as long as IQ tests have been around).
"It is correct that people marry and have children on bases other than just shared level of intelligence. (But living in the same town, and completing higher education at similar ages, and pursuing compatible occupations for marriage, etc. is correlated with IQ.) It is still far too early to say how rapidly human populations might see noticeable effects from assortative mating by IQ. It is reasonably clear that often-feared dysenic trends probably are NOT happening--the lowest-IQ people in the world population don't reproduce at all, and high-IQ people actually have reasonable numbers of children to replicate their genes. In any event, the favorable environmental trends have SWAMPED whatever genetic trends are going on for IQ in the whole human population, and people are getting smarter all over the world, according to the research on the Flynn effect.
"It is still a hard problem to identify anything at all meaningful and replicable about how gene differences influence IQ differences, even though it is now settled wisdom that they do. Human IQ, as the article says, is influenced by MANY genes, and many of those genes interact with one another in ways that are not understood at all yet."
1. http://www.nature.com/mp/journal/vaop/ncurrent/full/mp201410...