, sometimes known as the male , has well-known effects on competitiveness and status-seeking behavior. But does it also influence what men find attractive in women?

Research has suggested that men with naturally high levels of testosterone are more drawn to women with typically feminine faces: women with smaller jaws, bigger eyes, and higher eyebrows.

This makes sense because feminine features are thought to signal a woman’s “good ”, her high fertility, and physical quality: characteristics that our male ancestors evolved to pay extra special to. At the same time, facial femininity may also be related to characteristics men are less enamored of, such as unfaithfulness.

Testing for a link between mate preferences and natural hormone levels can never give us the whole picture. Perhaps men with high testosterone are different to men with low testosterone in some other way that explains their mate preferences. For example, men with high testosterone could be accustomed to winning at competitions, and expect attractive women to flock to them as a result. They could be more heavily muscled and more masculine-faced, thanks to the effects of testosterone on body growth, and may therefore suspect that their interest in feminine women will be reciprocated.

The only way to be sure that testosterone has a direct effect on men’s mate preferences is to conduct a proper experiment.

That’s right. You have to dose men up on testosterone.

A Hormone Massage

Brian Bird, a psychologist from Laurentian University in Ontario, Canada, did just that. He and his colleagues massaged a wad of gel into the backs of their male volunteers (who said science wasn’t fun?). Half of the men received a testosterone gel, normally used by men suffering from a testosterone deficiency. The other half of the men received a gel with no active ingredient. Of course, the men had no idea which gel was being massaged into their backs (and neither did the researchers who applied the gel — this was a double-blind study).

All the men then rated a series of female faces for . The faces were manipulated to appear more or less feminine.

On another day, the men returned to the lab and swapped groups. Those who had received testosterone gel on day one now received the placebo gel, and vice versa. Again, all the men rated the female faces.

Testosterone increases preference for femininity

The results of the study revealed that men rated the feminine-faced women more attractive when dosed up with testosterone rather than a placebo. Men rated the women’s attractiveness for both long- and short-term relationships, and preferred feminine-faced women for short-term relationships. This effect was more pronounced when men were dosed with testosterone.

Deeper analyses revealed that there was no difference between men after receiving testosterone or the placebo when it came to rating the women for short-term attractiveness. Men on testosterone, however, were less attracted to feminine women for long-term relationships than were men on the placebo.

Pointing out that earlier studies have suggested that feminine-faced women are more likely to cheat on their partners, the researchers claim that their study:

could suggest the possibility that T[estosterone] may increase men’s sensitivity to cues, perhaps triggering careful regarding the trade-off between a healthy partner with good genes (i.e., feminine faces), and /potential for defection (i.e., a more masculine face offering reduced likelihood of cheating) when it comes to selecting a long-term mate.

In other words, men high on testosterone may be more worried that their partner will leave them for a rival man, and aim to mitigate against this possibility by directing their attention towards women less likely to cheat when seeking a long-term partner. Men may care less about hooking up for a short-term fling with a woman likely to cheat, because the consequences of the cheating would be less severe.

The researchers concede that:

The present design did not allow a direct test of this hypothesis, so this remains entirely speculative as one of many possibilities for the pattern observed.

Follow up research may focus on this and other reasons for the changes in men’s preferences caused by spikes in testosterone.

For an audio version of this story, see the 20 December 2016 episode of The Psychology of Attractiveness Podcast.

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