Assortative mating -- among other things -- was one of the "problems" identified by Charles Murray in his book Coming Apart as a cause of greater inequality in American society[1]. As people "stick to their own kind", there are fewer opportunities for both economic and cognitive mobility: in the past, when marriage was determined by other factors, it was more likely that a highly intelligent person might have children with a much less intelligent person. That's increasingly no longer the case.
Interesting, but assortative mating is not a new phenomenon in the history of mankind. If anything, its impact has probably decreased significantly over the past centuries and decades. This makes it more difficult to take such explanations for growing income inequality at face value.
Let's put it this way: a "meritocratic" society has made intelligence inextricable from wealth and power in a way that was not true 100 years ago or earlier. If you were very smart in 1900, whether you worked in a factory or ran the factory was determined by your family's wealth and influence, and that also determined your pool of available mates. So instead of having a society where people practice assortative mating based on non-hereditary factors (wealth and power) people are mating based on intelligence and passing it onto their children. (I suppose familiar wealth and power is "hereditary" to a degree, but not with the durability of intelligence.)
> Are the U.S. economy and society more meritocratic than they were 100 years ago?
I think this question is more fuzzy at the 100-year time scale than the 200, 500, or 1000-year scale. It seems fairly uncontroversial that "merit" (whether by pure intelligence or some other metric for skill) had little to do with your station in life in 1514.
> The value of specific cognitive skills varies over time.
True. We should be careful not to anachronistically apply meritocratic assumptions about intelligence to other eras where raw intelligence and mental flexibility was less important than domain knowledge and practiced skill. But can we safely say that the Information Age has put a premium on the skills of those with high intelligence, and the benefits accruing to those workers over the last 50-60 years has skewed the mating priorities of many?
> There is far more to capability than intelligence. For example, there are very smart people who, due to lack of emotional or interpersonal skills, don't produce much.
Also true. Murray is careful to note that when we speak about meritocracy or the hereditary impact of intelligence, we can really only generalize about groups -- it can be wildly inaccurate for individuals. Can we safely say that the Harvard Class of 2014 as a group will have greater economic value over the course of their lives than the Anytown Junior College Class of 2014?
> a "meritocratic" society has made intelligence inextricable from wealth and power in a way that was not true 100 years ago or earlier
An interesting hypothesis.
1) Are the U.S. economy and society more meritocratic than they were 100 years ago? I've seen research saying social mobility has decreased recently (it didn't say about over 100 years) and is lower than in Europe, for example. Also, at least some research says that access to higher education depends significantly on the wealth of your parents; elite universities (and others) have problems attracting and graduating poor, smart students.
2) The value of specific cognitive skills varies over time. If 100 years ago, you had great ability to translate problems into efficient data structures and logic, I'm not sure how much economic value you would have. 50 years from now, I'm not sure how many humans will be writing code.
3) There is far more to capability than intelligence. For example, there are very smart people who, due to lack of emotional or interpersonal skills, don't produce much.
Suppose US society was meritocratic, intelligence is highly hereditary, and assortative mating happens. Then you'd expect low social mobility - people will have the same intelligence, and hence the same income, as their parents.
[1] http://www.nytimes.com/2012/02/12/books/review/charles-murra...