1. drug addiction
   bungee jumping
2. childbirth

Falling in love is like taking cocaine -- at least to your brain. There's a reason why both love and drugs are hard to quit. They activate pleasure centers in your brain that make you crave more.

1. serotonin
   testosterone
2. Rohypnol

Because a man's saliva includes testosterone, which increases sex drive in both men and women, a good make-out session can make you feel even more gaga for your guy.

1. men
   women
2. Both genders take about the same amount of time.

According to prominent anthropologist Helen Fisher, men tend to fall in love more quickly than women, because they are more visually oriented.

1. during full moons
   when a woman is ovulating
2. between 9 p.m. and 2 a.m.

Even when we're not looking to have children, our bodies respond to evolutionary urges telling us to mate. That may help explain why many studies have shown that women respond differently to men when they're ovulating. And men respond differently to women as well -- one notable study found that exotic dancers made more tips when they were ovulating.

1. 0.25
   0.7
2. 1.45

Researchers have determined that a waist-to-hip ratio of 0.7 is the most attractive to men; that number means that the waist is narrower than the hips. Waist-to-hip ratios between 0.7 and 1.18 would also be attractive; this measurement may indicate physical health and fertility.

1. motorcycles
   birth control pills
2. parental disapproval

Though motorcycles and a nagging mother may drive some women into the arms of a bad boy, birth control pills have been shown to affect women's ability to sniff out good genetic matches for themselves. Studies have shown that women can use their noses to find men who have different genes than their own, ensuring a good genetic mix in any potential children; however, women on birth control were more likely to find men with a similar genetic code more attractive.

1. the line that two people make across the room to flirt with each other
   a list of traits that turn a person on
2. slang for certain body language signals that drive women wild

"Love map" is a term coined by sexologist John Money, and it refers to an unconscious catalog of traits that we look for in a relationship. When we meet someone, Money posits, our brain goes through the love map determining how well this person measures up.

1. her reputation
   her clothing
2. her face

According to studies, a woman's face and its symmetry is the biggest turn-on for a man.

1. assortative mating
   sympathetic sexual recognition
2. punctuated equilibrium

We're often attracted to people who look, think and act the way we do, which is known as assortative mating.

1. two to four weeks
   between 18 months and three years
2. forever, if you're truly in love

Enjoy it while you can -- romance doesn't last forever, mainly because our brains can't handle the constant excitement. But that doesn't mean you have to break up; rather, it just means that two people have to work a little bit harder to keep the fire alive.