“Hypergamy refers to a system of practice of selecting a spouse of higher socio-economic status than oneself. Specifically, it refers to a widespread tendency amongst human cultures for females to seek or be encouraged to pursue male suitors that are comparatively older, wealthier or otherwise more privileged than themselves.”
Women, if left to nature, prefer to marry equally or up the scale. This means that very highly educated and successful women face a problem. It is also true of lower class women who choose not to marry someone who cannot or will not provide for them. Lower class men believe they have no great ability to move up the ladder; hence, you have 70% illegitimacy rates.
Incidentally, in studying primates one can clearly and closely correlate the body size difference between men and women to polygamous tendencies. For humans this results in men having weak polygamous tendencies—more than one but usually no more than three significant bondings. It matters little if these are all at once polygamous bondings or serial bondings (divorces). To be sure, individuals may overcome these patterns but only with some effort.