Diagnosed rates of autism spectrum disorders have grown tremendously over the last few decades. I find that assortative mating may have meaningfully contributed to the rise. I develop a general model of genes and assortative mating which shows that small changes in sorting could have large impacts on the extremes of genetic distributions. I apply my theory to autism, which I model as the extreme right tail of a genetic formal thinking ability distribution (systemizing). Using large sample data from the Centers for Disease Control and Prevention, I find strong support for theories that autism is connected to systemizing. My mating model shows that increases in the returns to systemizing, particularly for women, can contribute significantly to rising autism rates. I provide evidence that mating on systemizing has actually shifted, and conclude with a rough calculation suggesting that despite the increase in autism, increased sorting on systemizing has been socially beneficial.
This is an important paper, though I would stress the generality of the result; autism and systematizing may or may not be the best applications. If you are in some way genetically “extreme,” and suddenly better at finding/pairing with similar extremists, the numbers of that type in a population can rise relatively rapidly. We now have a very clear and useful model of how that works. One way to interpret this is to believe that the internet will, over time, increase human genetic diversity.