O.K., let's cut out all this nonsense about romantic love.Follow link for extended description of An illustration titled "How Do Fools Fall In Love?" shows two stylized figures of a man and a woman facing each other. Three numbered annotations point to their heads. Their hearts are connected by a common arrow. 16Chemicals may help explain (at least to scientists) the feelings of passion and compassion, but why do people tend to fall in love with one partner rather than a myriad of others? Once again, it's partly a function of evolution and biology. Men can size up youth and vitality in a glance, and studies indeed show that men fall in love quite rapidly. Women tumble more slowly, to a large degree because their requirements are more complex; they need more time to check the guy out. 17Still, that does not explain why the way Mary walks and laughs makes Bill dizzy with desire while Marcia's gait and giggle leave him cold. He rejects the idea that a woman or a man can be in love with two people at the same time. Each person carries in his or her mind a unique subliminal guide to the ideal partner, a "love map," to borrow a term coined by sexologist John Money of Johns Hopkins University.It is particularly true for those whom Dr. Michael Liebowitz of the New York State Psychiatric Institute terms "attraction junkies." They crave the intoxication of falling in love so much that they move frantically from affair to affair just as soon as the first rush of infatuation fades. 13Still, many romances clearly endure beyond the first years. What accounts for that? Another set of chemicals, of course. The continued presence of a partner gradually steps up production in the brain of endorphins. Unlike the fizzy amphetamines, these are soothing substances. Natural pain-killers, they give lovers a sense of security, peace and calm. 14Researchers see a contrast between the heated infatuation induced by PEA, along with other amphetamine-like chemicals, and the more intimate attachment fostered and prolonged by endorphins. It is the difference between passionate and compassionate love, observes Walsh, a psychobiologist at Boise State University in Idaho. 15Oxytocin is another chemical that has recently been implicated in love. Produced by the brain, it sensitizes nerves and stimulates muscle contraction. In women it helps uterine contractions during childbirth as well as production of breast milk, and seems to inspire mothers to nuzzle their infants. Scientists speculate that oxytocin might encourage similar cuddling between adult women and men. The versatile chemical may also enhance orgasms. In one study of men, oxytocin increased to three to five times its normal level during climax, and it may soar even higher in women. An illustration titled "How Do Fools Fall In Love?"From the earliest days, contends Fisher, the human pattern has been "monogamy with clandestine adultery." Occasional flings upped the chances that new combinations of genes would be passed on to the next generation. Men who sought new partners had more children. Contrary to common assumptions, women were just as likely to stray. If, in nature's design, romantic love is not eternal, neither is it exclusive. 9Lovers often claim that they feel as if they are being swept away. They're not mistaken; they are literally flooded by chemicals, research suggests. A meeting of eyes, a touch of hands or a whiff of scent sets off a flood that starts in the brain and races along the nerves and through the blood. The results are familiar: flushed skin, sweaty palms, heavy breathing. If love looks suspiciously like stress, the reason is simple: the chemical pathways are identical. 10Above all, there is the sheer euphoria of falling in love -- a not-so-surprising reaction, considering that many of the substances swamping the newly smitten are chemical cousins of amphetamines. They include dopamine, norepinephrine and especially phenylethylamine (PEA). Cole Porter knew what he was talking about when he wrote, "I get a kick out of you.""As long as prehistoric females were secretive about their extramarital affairs," argues Fisher, "they could garner extra resources, life insurance, better genes and more varied DNA for their biological futures...."6While Western culture holds fast to the idea that true love flames forever (the movie Bram Stoker's Dracula has the Count carrying the torch beyond the grave), nature apparently meant passions to sputter out in something like four years."If a woman was carrying the equivalent of a 20-lb. bowling ball in one arm and a pile of sticks in the other, it was ecologically critical to pair up with a mate to rear the young," explains anthropologist Helen Fisher, author of Anatomy of Love.Primitive pairs stayed together just "long enough to rear one child through infancy," says Fisher. Then each would find a new partner and start all over again. 7What Fisher calls the "four-year itch" shows up unmistakably in today's divorce statistics.No, their probe reveals that love rests firmly on the foundations of evolution, biology and chemistry.That makes them ripe for the more familiar phenomenon portrayed in the Marilyn Monroe classic The Seven-Year Itch."Men are looking for maximal fertility in a mate," says Loyola Marymount's Mills.Less than 5% of mammals form rigorously faithful pairs.