For example, an estimated 90% of bird species are socially monogamous but scientists have begun to discover using genetic and behavioral studies that in some species up to 75% of the offspring may come from “extra-pair copulations.” In other words, mama bird had some other sexual partners other than just the one she was tending the nest with.“A female who mates with several different males will have more genetically diverse offspring, boosting the chances that at least some of them will thrive.” Source
This goes for human females as well as other non-human animals and it is confirmed in our anatomy. The coronal ridge of the human penis is specifically designed to displace semen left there by another man or men. In addition, animals that engage in mate competition prior to copulation (like gorillas) tend to have small testes and penises. Animals that instead engage in sperm competition are more well endowed relative to body size (like chimpanzees and humans) because they need to have a large supply of semen on hand to inseminate multiple partners.
It is only with the rise of agriculture and the patriarchal social systems that eventually accompanied it that women’s sexuality was curtailed and monitored in some parts of the world. This was the only way that “true heirs” of land and property could be determined. Prior societies had few personal possessions and since fathers could not be definitively determined, lineage went through the mothers. This only changed 6–9 thousand years ago with the advent of patriarchy. Current cultures that are very community-oriented tend to care less about paternity also.
