It’s also important to look at human longevity with respect to cultural expectations of monogamy.
As recent as over 100 years ago, it was far more likely that an individual would lose his or her spouse at a young age. Remarriage by widows and widowers — also known as serial monogamy — was one way for humans to fulfill the need for sexual variety.
Today, the median age for first marriages is 28 for men and 26 for women. Disease is far less likely to kill someone in their prime and life expectancy hovers in the late 70s.
Because fidelity is considered the barometer of a successful marriage, this means that a person is theoretically expected to have one sexual partner for about 50 years.
This seems like a lot to expect of any human being — even the most honorable, ethical and moral.