The answer could lie in what evolutionary biologists call “parental investment theory.”

Whereas men can successfully reproduce by providing a few sex cells, a woman’s reproductive success must be tied to her ability to complete months of gestation and lactation.

During much of human history, a woman’s ability to choose a mate who was able and willing to assist in this process – by providing food or protection from aggressors – would have increased her reproductive success.

Evolution, therefore, shaped female psychology to attend to – and prefer – mates whose characteristics and behaviors reveal the willingness to invest. A prospective mate’s muscular physique (and, today, his big wallet) certainly indicate that he possesses this ability. But opening a car door or offering his coat are signs that he may have the desired disposition.