Many, many years ago, sex was something that people would typically have if they wanted children. Nowadays, it is something that lot of people have if they want to experience pleasure.
In the past, then, it was generally seen as having one purpose and in the present, it is generally seen as having another. Now, while there were people in the past who did have sex for other reasons, there is no denying how different it is today.
Separated
If it wasn't for the contraceptive pill, it is highly unlikely that sex would be seen in the same way as it is often seen today. Naturally, this has lowered the risk of a woman getting pregnant, thereby making it possible for her to have sex without needing to worry about what will happen after.
Along with this, a man can use a condom to stop his sperm from causing any problems.
So, in the same way that someone might have a piece of chocolate to experience pleasure, they can also have sex to achieve the same outcome.
It's Just Sex
Unlike most of their ancestors, this could be the only thing they know.