Thursday, January 29, 2009

Female brains and male skin tone

It is well known that women feel attracted to certain visual, auditory, and olfactory characteristics of men. This attraction seems to be hormonally regulated, as suggested by psychosexual studies of women at different phases of the menstrual cycle. In general, women are more strongly attracted to male characteristics during the estrogen-dominant phase of their cycle (first two-thirds) than during the progesterone-dominant phase (last third).

This cyclical change has been most recently shown by Rupp et al. (2009). MRI scans were used to measure how female brains process pictures of male faces that morphing software had either masculinized or feminized. The subjects were tested on days 10-12 and days 19-23 of the menstrual cycle. Measurements were taken of their levels of estradiol, progesterone, free testosterone, and total testosterone. The subjects also filled out questionnaires about their psychosexual profile (propensity for short-term sexual encounters, for sexual excitation, for sexual inhibition, etc.).

During the first time window (days 10-12), five brain regions showed a stronger neural response to masculinized faces than to feminized faces. No brain region showed the reverse pattern. During the second time window (days 19-23), only one region responded more to masculinized faces than to feminized faces. For both windows, some regions showed significant correlations between neural activation and hormone level. Estradiol correlated positively with neural activation whereas progesterone correlated negatively. The correlations were negative or positive for free and total testosterone. In some brain regions, neural activation also correlated with psychosexual variables.

What was driving these neural responses? What facial feature was turning these women on? In response to an e-mail, the lead author, Heather Rupp, told me that the morphing software had varied the shape of the male faces and their skin tone. The masculinized faces were darker-skinned and the feminized faces lighter-skinned. Her results may thus dovetail with my own findings on female preferences with regard to male skin tone, i.e., my subjects more strongly preferred darker male faces during the estrogen-dominant phase of their menstrual cycle than during the progesterone-dominant phase (Frost 1994).

References

Frost P. (1994). Preference for darker faces in photographs at different phases of the menstrual cycle: Preliminary assessment of evidence for a hormonal relationship, Perceptual and Motor Skills, 79, 507-514.

Rupp, H.A., T.W. James, E.D. Ketterson, D.R. Sengelaub, E. Janssen, and J.R. Heiman. (2009). Neural activation in women in response to masculinized male faces: mediation by hormones and psychosexual factors. Evolution and Human Behavior, 30, 1-10.

7 comments:

Tod said...

Preferences across the Menstrual Cycle for Masculinity and Symmetry in Photographs of Male Faces and Bodies These results suggest that a menstrual cycle shift in visual preferences for masculinity and symmetry may be too subtle to influence responses to real faces and bodies, and subsequent mate-choice decisions.

They were not artificially darkening photos or looking inside the brain with an MRI scanner though and their photos might have mixed naturally darker southern Europeans. Maybe northern and eastern Europeans are so white the constitutive skin color difference between men and women is less important in practice than the facultative skin color is. Darkened skin may suggests those personality traits found in outdoor types like surfers, skiers and climbers. Scars are a clear cut case, they advertise a personality that is not afraid to take risks, presumably scarred men would be avoided less during the first time window.
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Neanderthals were ambush predators, could their fur have functioned as camouflage, many woodland animals have reddish-brown coats, (foxes, squirrels, deer fawns).

Peter Frost said...

Thanks for the reference. I see two problems with the study you link to:

1) The 'masculinity' of the male photos is based on subjective criteria, i.e., ratings by a panel of 12 women. No information is given on the consistency of the ratings. This factor would have added a significant amount of noise to the results.

2) Most of the women on the panel were taking oral contraceptives. Consequently, their hormonal state would have been analogous to that of women in the last third of the menstrual cycle (i.e., the infertile phase). So I would not expect to see a correlation between their ratings and those made by fertile women. The two groups are cognitively different.

In my own research, women on contraceptives showed no menstrual cycle variation in response to male skin tone.

Tod said...

I should have read over Male skin color and ruddiness before commenting, it says
"At no point in the cycle was the darker male face more popular than the lighter one. It was simply less often disliked during the estrogen-dominant phase. As I saw it, higher estrogen levels seemed to be disabling a negative response to darker individuals. This negative response might be a social-distancing mechanism that keeps conflict readiness at a higher level during social interaction with males".

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Is there an alphabet gene?

Tod said...

Exposed skin has a tan long before the end of summer, facultative skin darkening adds melanin which results in vitamin D synthesis taking twice as long with same UVB intensity. (Yet another anomaly for those who hold to the 'skin lightening for maximization of vitamin D theory').

I've been wondering why the 'white' skinned tan?
The erythemal (burning) UV gets through pale skin and sunburned skin is inflamed and reddened, under selection for feminine looks reddish skin would be a very bad thing for women. "In humans, the adult male is ruddier in complexion than the adult female and male hormones greatly increase blood circulation in the skin’s outer layers." For women a tan would be far better than a red face.

Anonymous said...

How do you reconciliate the fact that women are looking for darker, more masculinized faces and the fact that european population skin complexion gradually lightened over the last 12000 years.
Is it possible that sexual selection for lighter skin tones was driven by males only ?
and that while males were looking for lighter skin, womem were looking for just the opposite?

strange world.
RG

Peter Frost said...

Tod,

I doubt that women are more prone than men to erythema. Even though female skin has less melanin, it also has more carotene, which blocks UV-A and neutralizes free radicals (Edwards & Duntley, 1939; Lee et al., 2000; White & Jahnke, 2002).

References

Edwards, E.A., & S.Q. Duntley. (1939). The pigments and color of living human skin. American Journal of Anatomy, 65, 1-33.

Lee, J., S. Jiang, N. Levine, & R.R. Watson. (2000). Carotenoid supplementation reduces erythema in human skin after simulated solar radiation exposure. Proceedings of the Society for Experimental Biology and Medicine, 223, 170-174.

White, A.L. & L.S. Jahnke. (2002). Contrasting effects of UV-A and UV-B on photosynthesis and photoprotection of β-carotene in two Dunaliella spp. Plant & Cell Physiology, 43, 877-884.

Anon,

Sexual preferences do not always translate into sexual selection. If too many women are competing for too few men, male sexual preferences will prevail over female sexual preferences.

I don't know whether women necessarily prefer darker-skinned men. In my research, this preference was stronger during the fertile (estrogen-dominant) phase of the menstrual cycle. But even then, the lighter-skined male face was still preferred by most subjects. I suspect this cyclical effect may have been stronger if I had been using color photos instead of B/W ones, but at present I really don't know.

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