One thing that has come up a lot in recent posts is the serious impact that the proliferation of obesity among women has had in the SMP/MMP.
If you go back to the 1950s, approximately 10% or so of the female population is significantly overweight. Most of these are women beyond prime marriage and dating years (which was also significantly younger back then). Today those numbers are well over 50% in many population segments.
One significant result from this is that a lot of groups that have raised their relative status, by pushing someone else to the back of the bus, still haven't improved the attractiveness of the women that will give them the time of day in the SMP/MMP. Let's illustrate...
Imagine a black man @1950-1960 who is around 25th percentile in terms of status among black men. He's not in significant competition with any other races in his SMP/MMP due to segregation. Therefore what he's likely to be able to attract for marriage is a black woman around the 25th percentile of attractiveness. What was that back in the 1950s? Essentially it was a non-overweight girl around the 25th percentile of attractiveness among non-overweight women. The lack of any significant numbers of marrying age black women who were overweight put even the 25th percentile black man in pretty decent shape.
That same black woman would be around the 50th + 1/4(50)---or around the 62nd or 63rd percentile today among black women! So even if we presume that other factors contrived to raise his effective status among society as a whole, is he better off?
The same man at the 50th percentile back then would likely pair with a woman who would be around the 75th percentile in today's distribution, and the man at the 75th percentile would probably get a wife around today's 87th or 88th percentile. Much above that and you probably can't use my basic assumptions, as the 95th-99th percentile women of today compare pretty well with those of yesteryear.
Is a large component of the baby boom's fertility just a predictable outcome of the fact that average Joe's, white and black, had more attractive partners and what Athol Kay calls 'structural alpha' (i.e., society wasn't going out of its way to weaken their position in the family or SMP/MMP)?