I. Sex was Invented by Ancient Scottish Fish

Somewhere around 385 million years ago a small bony fish invented intercourse in what is now Scotland. You wouldn't really recognized it as something to watch online in private, but none the less sex has been an important evolutionary feature of our world for almost 400 million years.

And keep in mind that this isn't the invention of sexual reproduction, that happened even earlier, the Scottish fish only innovated the touching part. Sexual reproduction started between 1 and 1.2 billion years ago.

Sexual reproduction broadly, and sexual intercourse as a strategy for said same is, as evolutionary strategies go, a huge success. You can see in countless examples how the lives of many species orbit around sex, how obsessive and even violent they can be around getting the chance to breed. Male Polar Bears fight all through mating season, Humpback whales are so aggressive toward females that it can endanger the calves they are still caring for. All of this effort and risk is almost certainly paid off, because if asexual reproduction was more adaptive it would be the norm. But sexual reproduction, with all its extravagant costs is still the most successful strategy for macroscopic life from rabbits to trees.

This is the first lesson of an empirical perspective on sex. It is first and foremost an evolutionary strategy with benefits and costs. And for any species that does reproduce sexually, sex is as important food. Keep this in mind, from the perspective of the species sex is as critical as air and water. Without sex there is extinction.

There are no animals who don't care about breathing. If you could make such an animal it would be doomed, it would never make it out of infancy. The same goes for food and water (all of the homeostasis issues). Sex is different, as the individual can survive without it. But you are a member of a species that can no more survive without sex than you can survive without air.

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature13825.html