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Still, 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. "That is one reason why it feels so horrible when we're abandoned or a lover dies," notes Fisher. "We don't have our daily hit of narcotics."
Researchers 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. "Early love is when you love the way the other person makes you feel," explains psychiatrist Mark Goulston of the University of California, Los Angeles. "Mature love is when you love the person as he or she is." It is the difference between passionate and compassionate love, observes Walsh, a psychobiologist at Boise State University in Idaho. "It's Bon Jovi vs. Beethoven."
Oxytocin 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.
One mystery is the prevalence of homosexual love. Although it would seem to have no evolutionary purpose, since no children are produced, there is no denying that gays and lesbians can be as romantic as anyone else. Some researchers speculate that homosexuality results from a biochemical anomaly that occurs during fetal development. But that doesn't make romance among gays any less real. "That they direct this love toward their own sex," says Walsh, "does not diminish the value of that love one iota."
A certain smile, a certain face
-- Johnny Mathis
Chemicals 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 are looking for maximal fertility in a mate," says Loyola Marymount's Mills. "That is in large part why females in the prime childbearing ages of 17 to 28 are so desirable." 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. "Age is not vital," notes Mills, "but the ability to provide security, father children, share resources and hold a high status in society are all key factors."