Scott Alexander in Astral Codex Ten:
“Female hypergamy” (from now on, just “hypergamy”) is a supposed tendency for women to seek husbands who are higher-status than themselves. Arguing about educational hypergamy (women seeking husbands who are more educated than themselves) is especially popular, because women are now (on average) more educated than men – if every woman wants a more-educated husband, most won’t get them, and there will be some kind of crisis.
Freddie de Boer’s Demographic Dating Market Doom Loop presents an argument that educational hypergamy is lowering marriage rates.
More here.