Toxoplasmosis might have something to do with it, if it is true. It's said to affect a high % of the population in countries like Brazil. Men become more aggressive/confrontational (the famous latin american "temper") and women become promiscuous, because that is what the host parasite wants... It spreads by social interaction.
I read somewhere that it "proves" that men are more natural violent and women are prmiscuous or polymonogamous by design, but there was not a shed of evidence to confirm that.
Some more about it;
http://www.viewzone.com/toxo.html
The key thing here is that you can get this brain parasite and not be affected by it. The effects are also subtle. you can have it your entire life without knowing, and since it spreads from cat shit, millions of people are walking around with it. It's pretty crazy stuff. But also interesting!
EDIT:
Yeah, according to wiki its big in Latin America;
"T. gondii infections occur throughout the world, although infection rates differ significantly by country.[63] For women of childbearing age, a survey of 99 studies within 44 countries found the areas of highest prevalence are within Latin America (about 50–80%), parts of Eastern and Central Europe (about 20–60%), the Middle East (about 30-50%), parts of Southeast Asia (about 20–60%), and parts of Africa (about 20–55%).[63]"
http://en.wikipedia.org/wiki/Toxoplasmosis