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Women who are on the birth-control pill may be more likely to pick provider types over aggressive, masculine specimens – a course that could potentially affect the health of their children, according to a controversial new paper from the University of Sheffield.

By doing away with ovulation, a woman's most fertile phase, the Pill may also make women less attractive to men, says the review paper, published in the current issue of the journal Trends in Ecology and Evolution.

While allowing that contraception has given women unprecedented control over their own fertility and reduced unwanted pregnancies and maternal deaths, the authors are concerned that women on the Pill may be choosing partners they "otherwise would not have chosen," said author Alexandra Alvergne, an evolutionary anthropologist from the university's department of animal and plant sciences who wrote the paper with colleague Virpi Lummaa.

Women who do not take hormonal contraceptives experience "dual sexuality" over the course of their menstrual cycle, write the authors, citing earlier research.

"Women prefer good genes during ovulation and good dads when they're not ovulating," Dr. Alvergne said.

During ovulation, women prefer men with symmetrical, masculine features. These men are aggressive, compete with other men, and in some cases exhibit "creative intelligence," write the authors. More importantly, their major histocompatibility complex genes – the ones that build our immune systems – are considerably unlike the individual woman's. According to earlier research, being attracted to a person with a different immune system is advantageous because the baby will inherit a larger arsenal to combat disease.

But during the infertile phase, women appear to prefer men who are more genetically similar to their relatives. Others opt for men who exhibit more "feminine" characteristics and have the means to invest in child rearing, Dr. Alvergne said.

The researchers say this dual strategy allowed ancestral women to "maximize their reproductive success."

To put it another way: "You fall in a long-term relationship with the caring, investing wimps and then you poach the good genes from the highest-status [masculine]guys. And the wimps hopefully make good stepdads and raise your kids," said Geoffrey Miller, an associate professor of human sexuality and evolutionary psychology at the University of New Mexico.

Since oral contraceptives interfere with ovulation and trick the body into thinking it is pregnant, women on the Pill tend to opt for provider types throughout their cycle, the authors write. Some women also pick men who genetically resemble their own relatives. The researchers say this is problematic: When such couples eventually decide to have children, their brood may be at risk for impaired immune function – and related health problems.

Also, "it could take a longer time to reproduce because you're too [genetically]similar to the partner," Dr. Alvergne said.

The authors contend that the Pill may also hurt a woman's chances to compete for partners, because men can detect a female's fertility status and like ovulating women better than others.

The authors cite a 2007 study conducted by Dr. Miller, who looked at the earnings pattern of 18 strippers who kept track of their lap-dance tips through two menstrual cycles. Ovulating dancers made $20 (U.S.) more an hour than their non-ovulating colleagues, Dr. Miller found.

The authors cite the lap-dance study as "among the most direct current evidence for Pill use disrupting women's attractiveness cycle" because "real consumer spending patterns (i.e. tips) probably reflect actual mate choice decision more directly" than hypothetical judgments.

Critics say the research cited in the current paper glosses over a litany of social, cultural and individual factors that help determine partner choice today.

"I think it's absolutely fascinating, but whether it actually means anything, I don't know," said James Trussell, who researches contraception and lectures on reproductive rights and health at Princeton University.

Dr. Trussell agrees that women's dual sexuality – something they don't experience while on the Pill – gave them an evolutionary edge, albeit mostly "millions of years ago."

Others say genetic whispers can't be ruled out in partner choice.

"You can't really deny certain biological urges, but on top of that you do have huge learning and cultural effects," said Anthony Little, a Royal Society Research Fellow at the University of Stirling in Scotland who studies face perception from an evolutionary perspective.

"There are certain things that seem to be cross-culturally agreed upon as attractive traits. Whether we like it or not, these things must have some sort of basis," said Dr. Little, whose own 2002 study cited in the current paper found that the Pill might change women's taste in men.

The authors are agitating for drug companies that market hormonal contraception to conduct trials on the "maladaptive side effects of Pill use on mate choice, attractiveness, relationship satisfaction, divorce probability and offspring health."

Dr. Trussell says fat chance.

"I can't imagine pharmaceutical companies doing studies of this," he said.

His bottom line is unwavering: "I trust women to make good choices about when and with whom to become mothers, and I think modern contraceptives enable many women to make their choices reality."

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