Women may prefer more masculine men when they're ovulating, but those aren't necessarily the traits they look for in long-term partners.
Researchers analyzed a number of both published and unpublished studies that looked at how women's sexual preferences change throughout their menstrual cycle, a University of California - Los Angeles news release reported.
Their findings suggest women evolved to prefer mates with traits such as "masculine body type and facial features, dominant behavior and certain scents" during ovulation, the news release reported. These traits are believed to have been marks of "high genetic quality" in our ancestors.
During the other days of the month (when the woman is not ovulating) she tends to look for traits in men that would have boosted survival rates in her offspring.
"Women sometimes get a bad rap for being fickle, but the changes they experience are not arbitrary," Martie Haselton, a professor of psychology and communication studies at UCLA and the paper's senior author said in the news release. "Women experience intricately patterned preference shifts even though they might not serve any function in the present."
The researchers collected raw data from 50 studies and converted the information into a mathematical format that allowed it to be statistically analyzed.
The findings showed a significant shift in women's preferences at different times in the menstrual cycle; the research is not as clear on exactly what male traits women are most attracted to during ovulation, but scent could be a strong factor.
In the scent studies analyzed women were asked to smell T-shirts that had been worn by males of "varying degrees of body and facial symmetry," the news release reported. Women tended to prefer the scent of "more symmetrical men" during the fertile days of their cycles.
These shifts in sexual preference have also been documented in animals. Female chimpanzees are known to have sex with different males during their fertile phase than they tend to prefer during the rest of their cycle.
"Until the past decade, we all accepted this notion that human female sexuality was radically different from sexuality in all of these other animal species - that, unlike other species, human female sexuality was somehow walled off from reproductive hormones," Haselton said. "Then a set of studies emerged that challenged conventional wisdom."
One hypothesis on why this occurs suggests that it is an "evolutionary adaptation" that worked to reduce offspring mortality rates. The "dual mating hypothesis" suggests women look for "good dad qualities" such as kindness and reliability when they are not ovulating.
"Ancestral women would have benefitted reproductively from selecting partners with characteristics indicating that they'd be good co-parents, such as being kind, as well as characteristics indicating that they possessed high genetic quality such as having masculine faces and bodies," Haselton said. "Women could have had the best of both worlds - securing paternal investment from a long-term mate and high-genetic quality from affair partners - but only if those affairs were timed at a point of high fertility within the cycle, and probably only if their affairs remained undiscovered."
Another hypothesis is that the phenomenon is simply a trait left over from our ancestors, but currently serves no significant purpose.
"If women understand the logic behind these shifts, it might better inform their sexual decision-making so that if they notice suddenly that they're attracted to the guy in the next cubicle at work, it doesn't necessarily mean that they don't have a great long-term partner," Haselton said. "They're just experiencing a fleeting echo from the past."
