This question originally appeared on Quora. Answer by Adriana Heguy, professor of pathology at NYU Langone Medical Center.

There is much more to reproduction than the act of sex. This question is written from the perspective of a male mammal only.

Pregnancy and childbirth are necessary conditions to "preserve the species", as the OP puts it. And pregnancy and childbirth are painful. Even for someone like me who had easy pregnancies, pregnancy itself is uncomfortable at the very least, and childbirth is always painful, sometimes excruciatingly so. Even when the process is quick. It is alsodangerous. For our species, even more so than for others, because of our erect posture and large headed babies. The death rate from childbirth has been steadily declining, though in the US is now rising again, but worldwide 800 women die from pregnancy or childbirth complications daily. These numbers may be small, compared to the number of live births that don't kill the mother, but it is still a risk.

And yet women do it over and over, not because they were horny and wanted to enjoy sex, or because they were raped, but because they want to have babies. And often their husbands or partners want to become fathers too. They want babies because they want to experience the love and the bond that being a parent creates.And many people have no desire for babies at all, and that's more than fine! There are too many of us and the worry right now is too many people on the planet, not too few.

Our species has largely dissociated sex for pleasure or bonding from sex for reproduction. Sure, there are unintended pregnancies that happened because both partners got in the mood and were not thinking straight about contraception, or, in some countries, did not have access to contraception. And when access to contraception is easier, most couples choose to have fewer babies because they want to give their babies their best opportunities in life and because, let's face it, almost no woman wants to be a baby incubator and nothing else. Raising kids is extremely rewarding but also taxing. Even for people like me, who think that having children is the most fantastic experience in the world, there is more to life than raising children.

The pleasure that we derive from sex was a factor at the dawn of a species, when we reproduced just like other animals do, not planned, but instinctual. But very early on humans attempted to control reproduction and dissociate sex from it. In other words, we wanted to have more sex than that needed for making babies. There are a variety of contraceptive techniques or natural plant derived products used as contraceptives very early on in history.

In any case, I honestly never understood the "preserve the species" worry. Why would we be interested in preserving the species? To me, that is not a value or a duty. If humans were to gradually disappear from Earth, what is it to me? As long as the humans that exist can live happy lives, the distant future is not my concern in terms of species survival. The reason why we worry about conservation of animal or plant species that are endangered is because the abrupt disappearance of any species can have devastating consequences for entire ecosystems, and even completely unforeseen consequences, especially if an equilibrium is altered very fast by human action. And while we are on Earth as a conscious species capable of planning, we should care about preventing major collapses and we should not be thoughtless and careless because plain stupidity and greed never helped any species.

So, long story short: humans reproduce even though it is painful and dangerous to do so. Humans do not largely reproduceause sex is enjoyable. The enjoyment of sex is a "trick" of evolution. Evolution does not care for this "trick" but clearly organisms without a strong impulse to reproduce do not pass on their genes efficiently, thus are less represented in the population. That's all there is to it.

If, from the male perspective, penetrating females was painful, many would still do it because they would want to become fathers, so they would put up with the discomfort and go soak their penises on ice water after the act, or something like that. Of course, the attachment to babies is also another of evolution's tricks. I totally fell for it, and not because I'm female. Many men fall for it too.

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