The Human Beast

Why we do what we do

Are Fertile Women More Attractive?

Subtle signals reveal when a woman may conceive.

Recent research argues that female sexuality changes in the days surrounding ovulation.
Like other mammals women are now thought to experience sexual heat, or estrus. Earlier sex researchers assumed that women had lost estrus entirely, or had "concealed" it, thereby keeping men in the dark as to when ovulation was actually taking place.

If men had no idea when women were ovulating, (which occurs in mid cycle), then they might be induced to stay around and care for offspring. The idea is that if men had no idea when women were fertile, then attempting to impregnate several women by showing up on those days of the month when each woman is most likely to conceive is a non starter.

The notion that women evolved concealed ovulation as a means of securing investment by men in themselves and their children has had a good inning but researchers have been chipping away at some of the its key assumptions. Is ovulation really hidden, or is it just not advertised? Are men completely in the dark about when women are most fertile in their cycle? Or do they find women more appealing when they are in estrus, just as other male mammals are drawn to estrus females?

Cues to being in heat
A lot of recent research looks for behavioral differences across the menstrual cycle relevant to women's sexual behavior and attractiveness to men. Contrary to the view that human estrus is cryptic, whether unadvertised, or "concealed," many cues can be used to distinguish between women who are close to ovulation and the same individuals at other times in the menstrual cycle.

Feminine lust is probably not one of them. There is no reliable difference in female-initiated sexual behavior between estrus and other parts of the menstrual cycle - as detailed in an earlier post. Some studies reported such a difference but many others did not (1). On the other hand, a great deal of research now indicates that women are more attractive at mid cycle (2).

Their body scent is more attractive to men. Their bodies also become more symmetrical due to changing shape of the soft tissues. Skin becomes paler, which is significant because women are slightly less pigmented than men in all ethnic groups. Their gait is sexier.  Even women's voices change, becoming more high-pitched when they are fertile (2).

As if this were not enough for a species supposedly having concealed ovulation, it turns out that men are also sensitive to when their female partners are ovulating because they are more attentive, and express greater jealousy at these times.

Despite all of the possible cues to their reproductive state, women themselves are not particularly good at detecting whether they are fertile or not, guessing correctly about 60 percent of the time versus a 50 percent chance of being right.

Whether they are aware of it or not, women who are fertile behave differently. In particular, they are more likely to wear revealing clothing and to behave in flirtatious ways (3). The researchers believe that clothing preferences around ovulation may reflect a ratcheting up of female-female competition. Another factor is that they are free of the discomfort of menstruation and pre-menstrual symptoms that may take up as much as a third of the cycle.

All of the above changes in women's attractiveness and flirtatiousness across the menstrual cycle may have a relatively simple hormonal explanation. They might be due to increases in estrogen levels, which peak around the time of ovulation. Other research finds that women whose estrogen (estradiol) level is high are both more physically attractive and more likely to think of cheating on their current mate (4).

Marilyn Monroe is sometimes given as a good example of a high-estrogen woman given both her curvaceousness and physical attractiveness and her proclivity to love them and leave them so far as boyfriends were concerned. She was also competitive with other women and mostly disliked by them. Moreover, she tended to move up the social ladder, dating leading figures right up to the U.S. president. Perhaps ordinary women feel a little bit more like Marilyn Monroe on days of the month when they are fertile.


1. Thornhill, R., & Gangestad, S. W. (2008). The evolutionary biology of human female sexuality. New York: Oxford University Press.
2. Bryant, G. A., & Braselton, M. G. (2009). Vocal cues of ovulation in human females.. Biology Letters, 5, 12-15.
3. Durante, K. M., Norman, P. L., & Haselton, M. G. (2008). Changes in women's choice of dress across the ovulatory cycle: Naturalistic and laboratory-based evidence. Personality and Social Psychology Bulletin, 34, 1451-1460.
4. Durante, K. M., & Norman, P. L. (2009). Oestradiol level and opportunistic mating in women. Biology Letters, 5, 179-182.

 

Nigel Barber, Ph.D., is an evolutionary psychologist as well as the author of Why Parents Matter and The Science of Romance, among other books.

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