The American science writer Jason G. Goldman recently wrote a piece on bbc.com about sex behaviours in animals, highlighting some interesting recent discoveries. For instance, researchers Alfonso Troisi and Monica Carosi spent 238 hours watching Japanese macaques - observing around 240 individual copulations (!) - and came to the conclusion that females can have a form of orgasms and that usually happens when copulating with males belonging to an 'higher social class'. Isn't it curious? Check also the following links, where you can find some more interesting stuff about our beloved Bonobos and gay-ish brown bears.
What we are saying now could get many scientists angry because one of the most important things to keep in mind when you talk about animal observation is to not follow the temptation of saying "Oh god! They are animals but they are acting like humans": ‘anthropomorphosis' isn't a scientific attitude. Nonetheless, the article by Goldman ends with quoting ethologist Jonathan Balcombe, who, in the Applied Animal Behaviour Science, seemed to conjugate a canonical Darwinian point of view with some interesting consideration about animals and sex. "Pain's unpleasantness helps steer the animal away from 'bad' behaviours that risk the greater evolutionary disaster of death. Similarly, pleasure encourages animals to behave in 'good' ways, such as feeding, mating, and...staying warm or cool."