You may think your sex life is imaginative. But, have you ever done the naughty with a partner not your own species? Some of our ancestors did. 23andme will tell you what fraction of your DNA comes from Neanderthals. The Inuit may be more adapted for the cold, because their ancestors cuddled up with the Denisovans. And there is tantalizing evidence that Pacific islanders may have mated with a hominid species not yet known. When H. sapiens spread from Africa throughout the world, our logo seemed to have been veni, vidi, futui.
Though it is now just a mathematical model without empirical validation, I like this explanation of why complex animals such as ourselves are born with germ cells, while that’s not the case in many simpler animals. Expect exceptions. Sex is weird because biology is complex.