Women who take oral contraceptives desire different traits in an imaginary man than women not on the Pill, according to a small study done in in Italy.
Whether that translates to their choices in the real world remains uncertain, but with more than 60 million women taking the Pill worldwide, the study authors write, the possibility that it changes mating dynamics is worth examining.
"It is important to reflect on these aspects from an evolutionary point of view, as changes in preference for indicators of genetic quality in a sexual partner are considered to be functional and adaptive," said Alessio Gori, lead author of the study and a psychologist at the University of Florence.
More masculine traits
Past research has found that when women view images of potential male partners during the most fertile time of their menstrual cycle, they tend to prefer the guys with more masculine traits.
Oral contraceptives prevent ovulation, so women on the Pill don't have a most-fertile time of the month.
To see if that makes a difference in what women want in a man, the researchers recruited 195 women between the ages of 18 and 50 from central Italy to complete questionnaires. These included a 20-item survey in which they rated on a five-point scale their preference for various indicators of masculinity, including athleticism, social class and shoulder width.
They also filled out a 56-item portion of the Minnesota Multiphasic Personality Inventory-2, a well-known personality test, to assess how masculine or "submissive" the women themselves were feeling.
Participants provided information about their menstrual cycles and whether they were using contraceptives. The women's average age was 32, and women who were significantly overweight or underweight were not included in the study.
Of the nearly 200 participants, 39% were taking the Pill. One hundred of the women were between days 11 and 21 of their menstrual cycle, which is when ovulation occurs and women are most fertile.
Gori and his team found that during the fertile days of the menstrual cycle, non-Pill users scored significantly higher on the questionnaire asking about preferred traits in an imagined man. Women on the Pill scored an average of just over 59 points on the survey, versus women not on the Pill, who scored about 73 points.
The higher score indicates that the women not on the Pill preferred men with more masculine characteristics, both physical and psychological.
Read: What do women want in a man?
When the researchers looked at the results according to the women's own masculinity level, they found that women with the most feminine and submissive personalities most preferred masculine attributes in an imagined man, whether or not they were taking the Pill.
Still, even in this feminine group, women on the Pill scored slightly lower in their desire for masculine traits, according to the report in the Journal of Sexual Medicine.
Little impact on reality
The results are intriguing, said Christine Drea, an evolutionary biologist at Duke University in Durham, North Carolina. But a woman's preferences for a hypothetical, made-up mate often differ from the men she chooses in real life.
"I question that a woman's fantasies about someone she might want to have sex with are necessarily predictive of the actual men with whom she tangos," said Drea, who was not involved in the study.
"Do hormones affect women's fantasies? Sure," but whether these fantasies actually predict behaviours is unclear, Drea told Reuters Health in an email.
For example, when asked to imagine an ideal mate, many women may envision a man with traits such as a strong jaw or a full head of hair.
"The vast majority of women, however, are not married to Brad Pitt or George Clooney. Instead, they're married to individuals with whom they're actually compatible – someone who acts right or smells right," Drea said.
So although the recent study indicates the Pill might affect some hypothetical ideal mate, such a fantasy might have little impact on actual mate selection.
"Having your normal hormonal variation be blunted chemically might make you care less about Brad or George, but you wouldn't have ever tangoed with Brad or George anyway," Drea said.
How people choose their partners
What makes us choose a partner?
The Pill influences choice of partner