Non coitus sexual activity and the brain Most animals will only engage in sexual activity that can result in reproduction. There are some exceptions; Bonobos, for instance, engage in a lot of sexual activity that does not involve coitus.

Human beings have a large range of sexual activities and fetishes that do not involves exual intercourse that can result in pregnancy (I am not referring to the use of birth control).

Oral sex, anal sex, and a variety of fetishes that do not involve coitus between a human male and female.

Given that the origin of sexual acts pertained to reproduction, somewhere along the line there has been development in the brain of humans and some animals, to include sexual activity for pleasure and acts that have no possibility of impregnating the female.

It can be argued why and what purpose these acts have, whether they are indeed part of the mating process. I am not interested in this so much as, the development in the brain which has offered this variation in sexual activity to some species.

This is not at all a social-psychological question, but a question focusing on evolution, embryology and the brain. From a macro to microscopic view, if applicable.

What is the difference in the brains for animals capable of these great differences in sexual activity and what part of the brain is responsible for this?

edit 

I am not assuming that all sexual activity involves pleasure. Dogs are known to dry mount other dogs in an assertion of power. So there does appear to be a development throughout evolution, as to the use of sexual activity and communicate and purpose. Definitely, human beings have a wide range of pleasurable sexual activity derived from non-vaginal intercourse, that the vast majority of species do not. It could be argues to be counter evolutionary for want of a better term, as, like much human behavior, it serves no purpose in the continuation of the species.. OR maybe it does. Either way, it is an interesting advent of behavior.
The first question is, what is normal human sexual behavior. The answer to this changes over time. For example, a hundred years ago masturbation was thought to cause physical degeneration and be a sin, today it is perceived as healthy, even recommended. Research shows that adolescent girls who masturbate have more and stronger orgasms as adults.

So, if anal sex is normal, then there should not be any basic difference in how the brain processes this from vaginal coitus. The difference between different normal sexual practices should be like that between different words that you hear (as compared to non-verbal sound, which should be processed differently). Maybe anal and oral sex where processed differently a hundred years ago or in different cultures. I don't know of any research into this, but maybe there is.

Paraphilias like fetishes, pedophilia, incest, voyeurism and other "deviant" sexual behavior have not been well researched. There are many psychodynamic and cognitive theories of paraphilias, but since you ask for the brain, I'll focus on biological theories here. The following is taken from the chapter on paraphilias in Davison &amp; Neale, Abnormal Psychology.


Since most paraphiliacs are men, it has been theorized that androgen plays a role in the etiology of paraphilias. Research into hormonal differences between paraphiliacs and normal people have had ambiguous results.
Sadism and exhibitionism appear to be caused by malfunctions of the temporal lobe (Mason 1997; Murphy, 1997).
Life experiences (like childhood abuse) are seen as the most important factor in a complex net of causes.


Besides psychological therapies of paraphilias (that will obviously influence the brain), there are biological therapies:


castration: results were highly ambiguous, so this therapy has been largely abandoned
medroxyprogesterone acetate lowers the testosterone level in men, cyproterone acetate lowers the androgene level, both reduce sexual appetency: this works in many paraphiliacs, but when they stop taking the medication the symptoms return; also, the substances can cause infertility and diabetes


As you can see, that's not much, and only two articles deal with the difference in brains. There may be more in recent articles.



The sources for the temporal lobe malfunction:

Mason, F. L. (1997). Fetishism: Psychopathology and theoriy. In D. R. Laws &amp; W. O'Donohue (Eds.), Sexual Deviance (pp. 75-91). New York: Guilford.

Murphy, W. D. (1997). Exhibitionism:  Psychopathology and theoriy. In D. R. Laws &amp; W. O'Donohue (Eds.), Sexual Deviance (pp. 22-39). New York: Guilford.