The Science of Seduction: Why Him, Why Her?

Jan. 27, 2009— -- Will you marry me?

It's a simple question made difficult because a lifetime of commitment rides on the answer. And how we arrive at this sought-after moment is one of the most complicated mysteries of our lives. How do we find love? Or more important, what exactly is love? Why do we feel it for one person and not another?

Biological anthropologist Helen Fisher has devoted a lifetime of research to these questions, and now she believes she has found some of the answers.

"I feel as if I've stumbled into Mother Nature's kitchen and found some of her recipes," Fisher said.

Watch the story Friday on a special edition of "20/20" at 9 p.m. ET

A seminal moment in Fisher's research occurred when she and her colleagues, Arthur Aron and Lucy Brown, started putting young lovers in an MRI machine. When they showed these subjects photos of their partners, a small region of the brain called the ventral tegmental area lit up on the scan. The ventral tegmental area produces the stimulant dopamine, and sends it to the brain's reward centers -- the centers for wanting, craving, motivation, focused attention and ecstasy.

For Fisher, it was a revelation.

"This made me realize that romantic love is not an emotion. ... It's a basic mating drive. A motivation system. A system to try to win life's greatest prize, which is the right mating partner," she said.

But while Fisher thought she knew what love was, it took a call from an Internet dating service to get her thinking about why we fall in love.

"They asked me a question: Why do you fall in love with one person rather than another? And I said, 'I don't know. Nobody knows.'"

Fisher found the question intriguing, and she began to suspect that the answer must lie somewhere in the brain.

"What I had to do," she said, "is figure out if there was any biology to your behavior."

Fisher began an exhaustive review of the scientific literature, looking, for example, at studies that have associated specific genes with certain behavior patterns, at studies that have examined the impact of recreational drugs on the brain and at studies that have examined the change in personality brought about by drugs like L-Dopa, which drives up dopamine and is given to people with Parkinson's Disease.

Explanation:

Doodles are used to determine if you are empathetic, assertive, risk taking, traditional, competitive, curious, or have a need for order.

Hearts: Negotiator, Geometric Shapes: Director, Repetitive Squiggle: Builder, Abstract Form: Explorer

If you were the publisher and had to choose a title for this book based on the cover below, what would it be?

A. Adventures on the Rhine
B. Anatomy of Friendship
C. Power Plays
D. Things Left Unsaid

Explanation:The title you select reflects if you seek intimate connections, build stable long-term ties, are logical and analytical or a thrill seeker. A. Explorer; B. Builder; C. Director; and D. Negotiator.

How does the length of the index finger on your right hand compare to your other fingers? Which hand in this photo most resembles your right hand?

Explanation:Testosterone builds the length of the ring finger in the womb. The longer your ring finger in relation to your pointing finger, the more likely you are to have mathematical, mechanical and/or musical skills.