Indeed love-making has been the subtext of the vast majority of art and poetry since the dawn of time.
And now a team of scientists in Indiana have worked out just why we make love.
It's to ward off parasites.
The research team discovered that humans and animals reproduce together, rather than simply cloning themselves, because it helps them to ward off parasites.
The same reason partly explains the existence of men.
The findings support the evolutionary theory that the blending of two animals' genomes creates an offspring with a new genetic code which makes it more resistant to attack.
Cross-fertilisation helps creatures stay a step ahead in the continuous "arms race" with parasites, which are forever evolving to try and infect them.
Experts at the University of Indiana have provided the best evidence yet after engineering two types of worms, some which could only reproduce by mating with each other and some could only clone themselves.
After exposing them to a harmful bacteria, worms that reproduced through sex survived fairly well while those that were asexual died rapidly.
Co-author Curtis Lively said: "The hypothesis predicts that sex should allow hosts to evade infection from their parasites, whereas self-fertilisation may increase the risk of infection.
"The coevolutionary struggle between hosts and their parasites could explain the existence of males."