The reversal test makes this sound a bit strange:
If you have a population with an average IQ of 100 and you add in an equal number of people with an IQ of 80 then after a generation, you will have a Gaussian with a larger variance. Hence there will be more geniuses due to more genetic variation.
Surely you don't believe that? I realize that this isn't a perfect reversal but that sounds very odd to me.
Anyway here is the crude model of intelligence that I working with - I admit I'm not an expert on this topic, and I have some reading up to do on the genetic basis of intelligence. Intelligence is a polygenetic trait that can be roughly (very roughly) modeled as a bunch of genetic sites with either a plus or minus alleles (keeping it simple with just 2 possibilities). The more plus alleles you have the more likely you are to have a high IQ (genes and intelligence aren't perfectly correlated). Populations with a higher average IQ have a higher concentration of plus alleles so the chance of receiving many of them is increased. But if you take away all of the people who due to bad luck received a very large number of minus alleles, you haven't altered the concentration of alleles in the gene pool that much - this is part of why regression to the mean occurs. But if you consistently select for people with a higher concentration of plus alleles, then the odds of any one child having a lot of plus alleles increases in the population. This is how artificial selection occurs in any trait that is polygenetic. Corn kernels are huge because the people who cultivated corn selected for the biggest corn kernels - yes there was a loss of genetic diversity and yes there was decrease in the variance, but that nevertheless what was observed were corn kernels that were bigger than any corn before.
Surely you don't believe that? I realize that this isn't a perfect reversal but that sounds very odd to me.
It would happen in your model, if there is no perfect overlap between the set of sites in one population and the set of sites in the other population. With two populations, you have more sites. The smartest possible mega-genius is from the mixed population and has + alleles on each site; none of the original populations can have a genius this smart at all.
To see that on less extreme rarity (and approximately for a large number of alleles), write do...
A long blog post explains why the author, a feminist, is not comfortable with the rationalist community despite thinking it is "super cool and interesting". It's directed specifically at Yvain, but it's probably general enough to be of some interest here.
http://apophemi.wordpress.com/2014/01/04/why-im-not-on-the-rationalist-masterlist/
I'm not sure if I can summarize this fairly but the main thrust seems to be that we are overly willing to entertain offensive/taboo/hurtful ideas and this drives off many types of people. Here's a quote:
The author perceives a link between LW type open discourse and danger to minority groups. I'm not sure whether that's true or not. Take race. Many LWers are willing to entertain ideas about the existence and possible importance of average group differences in psychological traits. So, maybe LWers are racists. But they're racists who continually obsess over optimizing their philanthropic contributions to African charities. So, maybe not racists in a dangerous way?
An overly rosy view, perhaps, and I don't want to deny the reality of the blogger's experience. Clearly, the person is intelligent and attracted to some aspects of LW discourse while turned off by other aspects.