If we are to only mate for the purpose of pro-creation?

Basic evolution. In every other animal, is a function of the female being in heat, which then turns on the male and then the fun starts. In the human, the female is never in heat, per se, and so is ually "available" at any time. The idea of as pleasure is, of course, to encourage reproduction. For humans, recreational is also possible, since there are not specific fertile periods where humans are and they are aual the rest of the time. In hunter gather societies, this may have been an evolutionary advantage in that a separate mating season would have distracted both genders from the other tasks required to survive. That lack of overpowering distraction at distinct intervals still serves the same purpose in society. And recreational is fun!! Praise be to evolution!!