A man who smells good to one woman doesn't necessarily smell good to another. "There is no ' Brad Pitt of smell,

Taking a contraceptive pill messes with Mother Nature in more ways than one, according to a new study by a scientist at the University of Liverpool in England.<br />In its effort to prevent pregnancy, the Pill alters a woman's sense of smell, which is one of the ways she decides, consciously and unconsciously, which men she is attracted to. When on the Pill, she is attracted to men with similar genes, the study revealed. With these men, she is more likely to have a miscarriage or a baby who has a compromised immune system, or suffer from infertility. When she is not on the Pill, her nose tells her to choose men who are genetically dissimilar, which increases her chances of producing a healthy child. It is Survival of the Fittest 101.In the study, which was led by Dr. Craig Roberts, lecturer in evolutionary psychology, 100 women were asked to indicate their preferences of six male body odor samples. Roberts tested women before and after their use of the Pill, which took research one step further from the 1995 study by Claus Wedekind that linked scent to selection by genes."Makes sense," says matchmaker Barbie Adler, president of Chicago-based Selective Search. "We don't usually hear the word 'smell' when people tell us if they like or don't like someone, but that is part of it. Usually, they use the word 'chemistry' or 'intuition.' "The Roberts study helps explain the science behind the intuition, says Rachel Herz, Brown University visiting professor of psychiatry and human behavior and the author of "The Scent of Desire" (William Morrow, $24.95). "Except for identical twins, each of us has a unique set of MHC (major histocompatibility complex) genes, which is the genotype for our immune system," explains Herz. "Our body odor is the external manifestation of this."<br />A man who smells good to one woman doesn't necessarily smell good to another. "There is no ' Brad Pitt of smell,' " says Herz.When people meet potential mates, their noses tell them if they have similar or dissimilar genes and immune systems, according to Herz and Roberts. Mating with someone with similar genes increases the chances of a baby having negative recessive traits such as Tay-Sachs.In terms of hormones, the Pill tells a woman's body she is pregnant. This could explain why women on the Pill choose men who smell like family members, because they could protect her while she is vulnerable. Off the Pill, nature takes over, so she seeks genetically dissimilar mates.The time of month affects a woman's ability to sniff out mates too. Her gene-smelling ability is keenest around ovulation, says Herz, when it exceeds a man's. During menstruation, her ability is less than a man's. Men, on the other hand, are more likely to use sight to locate what their eyes tell them are fertile mates: women with healthy-looking skin and hair and a waist-to-hip ratio of 7:10.The Pill isn't the only way people alter their scent detecting, adds Herz. "Men can mask their odors by wearing, for example, colognes," she says. Does this mean a woman will ditch a man when she discovers his real body odor? Not necessarily, says Herz. "If he has masked his real smell with a strong fragrance such as Axe, and you fall in love with him, and then he later reveals his real smell, it will be positive to you because of your positive feelings for him," she says.Does all this fly in the face of society's definition of eligible men as rich, successful and intelligent? Herz's studies have shown that body odor wins. One of her test respondents said, "If I'm with a guy who smells really good, nothing else about him matters."Yet, Herz offers an explanation of why so many successful men seem to have their choice of women: On average, these men are healthier and not plagued with illness, so their body odor is more likely to be pleasant.<br />"This doesn't necessarily mean that Donald Trump is the right MHC match for model Melania Knauss," writes Herz in her book. "But it does mean that he probably smells better fresh out of the shower than someone his same age whom you meet at the unemployment center."Roberts' study, which brings attention to a field that is ripe for additional studies, raises as many questions as it answers, says Herz. Yes, she says, "I don't like the way he smells" is a common complaint among women in marital counseling. And, she says in her book, infertility clinics report that couples who are MHC-similar have a harder time conceiving.But, are women messing with the future of our race by choosing mates while they are on the Pill? That, says Herz, is what we still don't know.Next up for Roberts, he said in an e-mail, is to study couples' experiences outside of the laboratory. This could tell scientists, he said, the secondary effects "in terms of within-couple infertility and, potentially, on child health and relationship outcomes."Not to mention, he said, the possible "breakdown of relationships when women stop using the contraceptive pill."

A man who smells good to one woman doesn't necessarily smell good to another. "There is no ' Brad Pitt of smell,

Taking a contraceptive pill messes with Mother Nature in more ways than one, according to a new study by a scientist at the University of Li...

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