I believe there is some natural nurturing qualities that females have over males. I also believe our society has conditioned them in many instances to make them feel incomplete if they do not produce off spring.
Little girls are often given baby dolls to care for. Some of these dolls come with diapers, bottles, strollers, changing clothes, brushes, combs, and in some cases food. The girls are being groomed to behave in ways similar to their moms.
Little boys by contrast are given toy cars, guns, remote boats and planes, fire trucks, balls for various sports, and other self-indulgent things to do for fun. Nurturing/ taking responsibility for others is not ingrained in them as activities to do for fun.
By the time a girl reaches elementary school she most likely has practiced raising several baby dolls, cooked meals in her Easy-Bake Oven and numerous other domestic activities.
This kind of thing stays with you subconciously.
They don't call those years the formative years for nothing!