Through functional magnetic resonance imaging, or fMRI, scientists for the first time peered into the brains of fully conscious nonhuman primates (marmoset, a tree-dwelling Brazilian monkey) to learn what's really on their minds when it comes to sex.

Common marmosets, like humans, live in family groups and have to make careful choices when confronted with the scent of an attractive female, a team of marmoset experts led by Charles T. Snowdon, UW-Madison professor of psychology, discovered.

"We were surprised to observe high levels of neural activity in areas of the brain important for decision-making, as well as in purely sexual arousal areas, in response to olfactory cues," Snowdon says. "Lighting up far more brightly than we expected were areas associated with decision-making and memory, emotional processing and reward, and cognitive control."

The marmoset fMRI findings add strong weight to the mounting evidence that, when faced with a novel, sexually attractive and receptive female, males even in monogamous species aren't necessarily just acting on some primal urge to procreate, without a second thought. Rather, they exhibit highly organized, complex neural processes. >from *Sex In The Brain: How Do Male Monkeys Evaluate Mates?*. February 3, 2004.

related context
> science in the bedroom: a history of sex research by vern l. bullough. 1994
> the evolution of human sexuality by don symons. 1979
> a history of sex by andres serrano. 1997. more...
> common biological ground for maternal and romantic love in humans. february 13, 2004
> neurobiological basis of romantic love. november 26, 2003
> conflict interaction of couples. october 27, 2003
> biodiversity include sexual diversity. june 14, 2002
> next sex: sex in the age of its procreative superfluousness. ars electronica. september 2-7, 2000

imago
> contained marmoset sex life?

Researchers have suggested that size matters when it comes to sex - the size of part of the brain, that is.

According to David Reutens at the University of Melbourne, Australia, a person's sex drive may be proportional to the size of their amygdala, a small 'emotion' centre nestled at the base of the brain... a larger amygdala might boost the likelihood of a sexual trigger leading to arousal.

The amygdala is unlikely to account for sex drive on its own. It is intimately linked to other brain regions, including the hypothalamus, which sets off physical responses to arousal, such as erections. From "Brain size matters for sex: The fear centre finds a role in arousal" January 21, 2004

http://www.nature.com/nsu/040119/040119-4.html

What defines a sex? Although we tend to think there are only two - males and females - there are many different ways to mix and match the attributes of sexes.

In fact, different species have evolved a bewildering number of ways to mix and match the attributes of sexes. Some do not have males and females, but have adaptations that mean each individual performs a specific role during sex. There are other species of which every member is sexually equivalent, but individuals nevertheless divide into groups for the purposes of mating. And in some species, individuals make both eggs and sperm. This biological diversity has produced a semantic muddle among biologists—everyone who thinks about the evolution of sexes seems to have a slightly different take on what a sex is.

As things stand, there are three main aspects to the definition of a sex: who you are, who you can mate with, and who your parents are. The third part of this trinity—parental number—shows the least variation in nature. No known organism needs more than one mother and one father. But even this assumption is now starting to break down at the level of biological systems. In a recently discovered hybrid system within the harvester ant genus Pogonomyrmex, queens must mate with two types of males to produce both reproductive individuals and workers. These ants are the first species known which truly has more than two sexes—with colonies effectively having three parents—. From "Everything You Always Wanted to Know about Sexes" by John Whitfield. PLoS, june 2004.
http://www.plosbiology.org/plosonline/?request=get-document&doi=10.1371/journal.pbio.0020183