It's actually proven out long term in the genome. Only about 40% of all men who've ever lived had children. 80% of women have. Women have higher selectivity toward partners.

Wilder, J. A., Mobasher, Z., & Hammer, M. F. (2004). "Genetic evidence for unequal effective population sizes of human females and males". Molecular Biology and Evolution, 21, 2047-2057.

Just one of the usual MRA talking points.

Depends if species is monogamous, basic ethology stuff.