For a species to survive, they needed to have the innate desire to reproduce. In humans, perhaps that would normally be referred to as horniness, but in the end, humans are still animals no matter how much they evolve past their roots.
Even for a long lived species like elves, reproducing had to be a part of their nature, otherwise they couldn't survive. The real difference between humans and elves however was that elves were much less fertile than humans and conspection would therefore take a lot longer to achieve. While humans would naturally be able to reproduce as soon as puberty hit, there is only the short span of forty to fifty years before they would then lose that ability.
Sometimes the time frame was even less.
