There is one thing that makes us unique: the pimp. In nature there are myriad ways of having sex, and humans undertake almost all of them, from the gang rapes of Right Whales, to the monogamy of Terns. We are not only a hypersexual species, like Bonobo and Dolphin, whose females can instigate sex at will (unlike most sexual animals that have a specific season), but the most hypersexual vertebrate. In all that plethora of sexy time, no other animal has a pimp, madam, matchmaker, or priest to sanctify their unions.

I wrote a tripartite series of posts, starting with Tricks of the Trade, that goes into more detail.