Saliva has testosterone and estrogen. When you kiss, you're having a chemical experience.

Every time you cuddle with your children, you're likely to be driving down your testosterone.

Real competition can drive up testosterone, which boosts libido.

When you fight, anger drives up testosterone in both men and women.

From my studies of genetics and neuroscience I have come to believe that people fall into four broad personality types - each influenced by a different brain chemical: I call them the Explorer, Builder, Director, and Negotiator.

Women are very attracted to a low voice because it's linked to testosterone, which for millions of years was a sign that men had very good spacial skills and would have been very good at hunting and finding their way back home.