Dr. Michael Gurian has some very interesting things to say about the relationship between men and women, and how the two genders are different.

One of the things he discusses in his book, "What Could He Be Thinking?", is how and why there's a link between sex and aggression. According to Gurian, the two are linked to a man's sexual biology, but is a lesser case in women. Read on to see some of the reason's he found this to be true.

Men's dominant hormone is testosterone, which is also called the sex and aggression hormone. Because of its high levels, a man has a higher sex drive and is more aggressive. However, aggression doesn't necessarily mean violence, it could mean just about a hundred different things from the way he focuses on advancing in the workplace to being the best at something such as a sport. When a women has a high testosterone level, she, too, will have a higher sex drive and feel more aggression.

A man needs the brain chemical called Vasopressin in order to easily engage in sexual activity. It is an aggression chemical found in a male's amygdala and anterior hypothalamus. Vasopressin helps a male to mark his territory, as well as help with sexual aggression. However, in the case of a female, this chemical curtails courtship functions.

Dopamine is a huge part of a man's sexual aggression. When removed, he can lose all sexual desire, whereas a female isn't affected at all.

Check back with us for Part II.