Women only stay with men for security, and men only stay with women for sex. It’s a cynical view of human relationships, but researchers now say it is the driving force behind the evolution of monogamy — and women started it. By offering sex all the time, females in monogamous species disguise whether they are fertile and trick males into sticking around.
“The male has no cue,” says Enquist. “All he can see is the behaviour of the female.”