Ever since Darwin there had been an assumption among evolutionary biologists that females were coy and choosy in their sexual behavior while males were the ardent, promiscuous sex. Even though important advances in gender equality have been achieved since then, “most Darwinian models of human origins incorporate females only as passive objects of male competition,” wrote biological anthropologists Craig Stanford and John Allen as the 20th century came to a close.
And yet these female langurs were observed actively pursuing males from neighboring troops while, according to the prevailing theory, they should have been chaste rather than chasing. What was even more surprising was that they would exhibit these sexual advances at any stage in their estrous cycle, sometimes even when they were already pregnant.
“Under some circumstances,” primatologist Sarah Hrdy wrote in her classic 1977 book The Langurs of Abu, “females are continuously sexually receptive, a pattern previously thought to occur only among human females.”
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Primatologists refer to langur societies as polygynous, in that they are composed of multifemale, single-male groups. Darwin’s theory of sexual selection held that these females should choose the most impressive male in their troop to ensure the hereditary success of their offspring. But here was clear evidence that females would actively engage in “adulterous solicitations” with males from other societies. As Hrdy revealed to a scandalized scientific community, the genetic benefits that came from seeking extra-pair matings—while maintaining the support of an existing partner—meant that evolution could favor females who choose to cheat.
Read the full, original story: Promiscuity is pragmatic
