Q: In a nutshell, why do people fall in love?

Dr. Fisher: I’ve come to think that romantic love is one of three basic brain systems that evolved for reproduction. Each evolved for a reason: The libido evolved to get you out there looking for partners. Romantic love evolved to enable you to focus your energy on just one person at a time, conserving time and energy. And attachment, the feeling of security you can feel with a long-term partner, evolved to help you stay together long enough to raise your kids.

Q: Why does being in love feel so good?

Dr. Fisher: Because some of the most powerful brain circuits for pleasure are triggered. The main chemical involved is dopamine, which produces feelings of euphoria, energy, sleeplessness and focused attention on your beloved. Biologically speaking, you’re experiencing something similar to a high.

Q: Is there such a thing as love at first sight?

Dr. Fisher: Yes. It probably happens to men more than women because men are more visual, but I think we can all remember times when we felt an instant attraction to someone we barely knew. It has a practical purpose: in the animal kingdom you can’t spend three months discussing your résumé; you need to feel instant sparks to start the reproductive process.

Q: Is falling in love all about timing?

Dr. Fisher: Timing is important. The perfect partner can sit right next to you at a party and you might not notice him or her if you’re too busy at work, enmeshed in another relationship or otherwise preoccupied. But if you’ve just moved to a new city, recovered from an unsatisfying love affair, begun to make enough money to raise a family, are suffering through a difficult experience or have a good deal of spare time, you are ripe to fall in love.

Q: Is there anything we can do to make someone fall for us (or make ourselves fall for someone)?

Dr. Fisher: Do new things together. Novelty and excitement all drive up the activity of dopamine and norepinephrine in the brain. These neurotransmitters are associated with energy, elation, focused attention and motivation — all central traits of romantic love. So as you do novel things, these chemicals hop into action and may just push you over the threshold to fall in love.

Q: Is there anything you can do to make yourself stop loving someone?

Dr. Fisher: Some people, especially women, tend to talk about a failed relationship so much that they re-traumatize themselves. Instead, get rid of your ex’s cards and letters. Don’t call or write. Get some sunshine and exercise, because both can change your brain chemistry.

Q: What’s the difference between love and lust?

Dr. Fisher: Lust generally dissipates after physical intimacy and returns hours or days later. You can feel it for several people at the same time and not necessarily feel jealous. But when you’re in love, you are very possessive. And romantic feelings don’t dissipate after becoming physical with someone; in fact, they can intensify.

Q: Does physical intimacy make people fall in love?

Dr. Fisher: It can trigger love — probably because afterwards, there’s a peak in dopamine activity. So watch out — you might unintentionally fall for someone.

Q: Do feelings of love die over time, and is there any way to bring them back?

Dr. Fisher: The first intense period of love can last one to three years. After that, these feelings subside. But if two people are compatible, there are many ways to renew a flagging partnership. Novelty can spur romance; physical intimacy can trigger it, too. Do some of the things that you used to when you were first dating.

Q: How important a role does chemistry play in love?

Dr. Fisher: I believe that when the chemistry of one personality meshes well with the chemistry of another, it will continually combust throughout the relationship — keeping both partners together and happy during dry spells when feelings of romance are low.

Q: How do men and women experience love differently?

Dr. Fisher: Men fall in love faster than women do. Women take longer because they have to create a “memory trail” of their mate’s behaviors. She has to remember what he promised, what he’s done for the partnership, and what he failed to do.

Q: What do men look for in a mate?

Dr. Fisher: Men are more likely to choose women who display signs of youth and beauty — the first time that they marry, men around the world tend to marry women who are three years younger than themselves. Men are also attracted to women who “need” them. Men want to be helpful.

Q: What do women look for in a mate?

Dr. Fisher: Women are attracted to partners with money, status and ambition — one study found that American women seek partners who offered financial security twice as frequently as men do. If men look for “arm candy,” then women look for “success magnets.”

Q: Can someone truly love more than one person?

Dr. Fisher: No. I think you can feel lust for more than one person, and feelings of attachment for more than one person. But not love. As the Indian aphorism goes, “The lane of love is narrow; there is room for only one.”

Q: What’s the biggest mistake people make when it comes to love?

Dr. Fisher: Some people fall in love before they really know their partner and marry in this state of romantic rapture. They should probably wait until that intense early phase wears off so they can see the flaws in the relationship before they dive in for good.

Q: Having reviewed so much scientific data on love, what would be the most important thing we’ve learned?

Dr. Fisher: To me, the most important thing that scientists have learned is that romantic love was not invented by the troubadours in 11th-century France. We have now found love poetry from the ancient Sumerians written some 4,000 years ago, as well as evidence of romantic love in over 150 societies. It’s given me a deep sense of connection to people everywhere: We’re all alike in some basic and beautiful ways.