There is certainly an inner drive, more pronounced in women, because species without such a drive don't make it though natural selection.

Really? The reproductive urge in humans seems to be more centered on a desire for sex rather than on a desire for children. And, in most animals, this is sufficient; sex leads directly to reproduction without the brain having to take an active role after the exchange of genetic material takes place.

Humans, oddly enough, seem to have evolved adaptations for ensuring that people have unplanned pregnancies in spite of their big brains. Human females don't have an obvious estrus cycle, their fertile periods are often unpredictable, and each individual act of copulation has a relatively low chance of causing a pregnancy. As a result, humans are often willing to have sex when they don't want children and end up having them anyway.