Having now learned the terminology, assortative mating could indeed lead to speciation in the general case; it's just a special case of sexual selection. I find it highly unlikely that that will happen with human intelligence, though (despite the fact that it's been used in fiction more than once). The reason is that there's a limit to how big the variance can get- it doesn't grow forever, it grows until limited by other factors (i.e., there are only so many intelligence-promoting alleles that you can possibly have).
It would take intentional segregation to cut off all gene flow between the upper and lower halves of the intelligence Bell curve, thus allowing other differences to pile up between the populations, to cause speciation. And as noted elsethread, that's called eugenics and generally frowned upon in polite society.
> The reason is that there's a limit to how big the variance can get- it doesn't grow forever, it grows until limited by other factors (i.e., there are only so many intelligence-promoting alleles that you can possibly have).
What makes you think that? You could say the same thing about seed size in plants, but comparing modern corn kernels to wild type seeds provides a clear counterexample.
You should look at the type of stuff they've done in plants and animals. Here's a paper on the selective breeding of fruit flies for flight speed. The results are astounding:
"The mean apparent flying speed of both lines increased from approximately 2 to 170 cm/sec and continued to respond at diminishing rates, without reaching a plateau, for 100 generations. Competitive fitness tests in generations 50 and 85 showed minimal or no fitness loss in selected lines compared to controls."
Interestingly, the current mating and segregation trends, to the extent they exist, appear to be completely "natural" and lacking in premeditation. Can't help but wonder if modern humans are not the result of a process that left the Neanderthals ( pre-modern humans, whoever they were) behind. I'm no expert, but I don't think a complete lack of gene flow between groups is thought to be required for the process of speciation.
It would take intentional segregation to cut off all gene flow between the upper and lower halves of the intelligence Bell curve, thus allowing other differences to pile up between the populations, to cause speciation. And as noted elsethread, that's called eugenics and generally frowned upon in polite society.