In 2006, the porn industry raked in nearly 13 billion dollars. Hardly surprising, given that the there's definitely a market for it. According to a survey by the Pew Internet & American Life Project, 26% of male Internet users visited adult websites compared to 3% of women. So what is it about watching naked strangers have sex that leaves men so in awe?

It all boils down to evolution. The male brain is hard-wired for easy arousal due to their desire to spread their seed, meaning that men are ready for sex whenever opportunity knocks. But what about guys who are already in a long-term relationship? Could it be a warning sign of things to come? Psychologist and sex therapist Russell Stambaugh tells WebMD:
"Often, one partner has a porn interest, and the other thinks that's a problem. It rarely is. The best studies suggest that only about 5% of porn users have a problem that interferes with their daily life."