Oct. 7 (HealthDay News) -- Could birth control pills be taking human evolution in a whole new, and possibly detrimental, direction?

A review of past research finds that, by altering hormonal cycles, the pill might affect choice of mates among members of both genders in a way that could hinder successful reproduction in the future.

"The use of the pill by women, by changing her mate preferences, might induce women to mate with otherwise less-preferred partners, which might have important consequences for mate choice and reproductive outcomes," said Alexandra Alvergne, lead author of a study appearing in the October issue of Trends in Ecology & Evolution.

"One prediction is that offspring of pill users are more homozygous than expected, possibly related to impaired immune function and decreased perceived health and attractiveness," according to the report by Alvergne, a postdoctoral research associate in the department of animal and plant sciences at the University of Sheffield in England, and colleague Virpi Lummaa.

But another expert thinks this new revelation on the pill, which did indeed revolutionize sex in the 1960s, may have been over-interpreted.

"The study was about female preferences in their relation to hormones in the cycle but that's not the same as your mate selection for a long-term relationship," said Dr. William Hurd, a reproductive endocrinologist at University Hospitals Case Medical Center in Cleveland. "If you don't take into account society maybe we're all animals, but in social situations I don't think there are many women who change who they would mate with at different times of the month. It might change desires or perceptions but, gee whiz, that's a long stretch to changing who you would date, or even who you would go to dinner with."

Women who are ovulating tend to be attracted to so-called "manly men," those with more masculine facial features and traits of dominance and competitiveness, according to background information in the study. They also tend to prefer the man who is not like them, genetically speaking.

And men, given a choice, will gravitate towards an ovulating female rather than a non-ovulating female.

But women on the pill are more consistently in a state that mimics pregnancy, the authors stated.

According to the study authors, who stress that "modern contraception has improved the quality of life worldwide," 100 million women around the globe are on the pill.

Alvergne and Lummaa are hoping the paper will spur further research.

"There are important limitations from previous studies, due to the fact few of them have been addressing the question as their main focus," Alvergne said.

Future research should focus on two questions in particular, she said: Does use of the pill affect marital relationship, satisfaction and durability; and does it affect the ability of couples to reproduce?

But Hurd thinks there are other trends changing how humans date, mate and reproduce far more radically than artificial hormone cycles.

"Probably the biggest change in my lifetime is how people meet each other: online and using programs that match them for compatibility," he said. "That's probably going to have a massive effect on how people end up dating and ultimately reproducing. Just because you like someone with a square jaw in the middle of your cycle probably doesn't affect who you end up with."

SOURCES: Alexandra Alvergne, Ph.D., postdoctoral research associate, department of animal and plant sciences, University of Sheffield, U.K.; William Hurd, M.D., reproductive endocrinologist, University Hospitals Case Medical Center, Cleveland, Ohio; October 2009, Trends in Ecology & Evolution