Just about every article I read on women’s preferences for sexual dimorphism in men points out that the data are consistent with the good genes hypothesis. There are a couple of technical variations of this hypothesis, but they all are based on the reasonably well-established connection between testosterone and impeded immune system functioning. The idea is: testosterone interferes with immunity so males who display increased phenotypic influences of testosterone must have better genes, in order to combat the toxic effects of the hormone on the immune system. So far, so good. The hypothesis is perfectly reasonable: however, it is far from substantiated. A central issue for me involves the notion of trade-offs: it is possible that the larger muscles and increased status-seeking that are associated with testosterone might result in higher status which could produce adaptive benefits, e.g., increased access to food which, at least theoretically, could compensate for the correlated decrease in immune functioning. I am not arguing that this has been shown – but I am emphasizing the hypothetical nature of the good genes hypothesis.
Regardless of the veracity of the good genes hypothesis, the beauty literature is lacking in proximal explanations for women’s increased interest (during ovulation) in sexually dimorphic features in men. Broadly speaking, the evidence continues to build that women find moderately increased levels of sexual dimorphism in males more attractive during fertile periods than during non-fertile periods (e.g., Johnston et.al, 2001). The question is, why?
My hypothesis is that ovulating women have higher levels of libido (to use the vernacular, they are a little hornier) and, when hornier, are more likely to prefer males who look like virile, competent, enthusiastic – good – lovers. Evidence is accruing that women have increased interest in sex during/around ovulation (e.g., Wilcox, et.al. 2004; Tarin & Gomez-Piquer, 2002). I also believe there is some evidence to support the assertion that the increased attraction to sexually dimorphic characteristics around ovulation could be due to the belief that such features signal competence as a lover rather than an attraction to increased masculinity per se.
Using frame numbers in the quick time movie (the format the morphed faces were presented in): the average attractive male face was depicted in frame 284 (below middle). When peri-ovulatory, women found frame 245 (below right) the most attractive.
This shift in preference is a shift toward both increased sexual dimorphism and to the perception of increased competence as a lover. Since the average optimally attractive male face (frame 245) more closely approximates the face that looks like the optimal lover (approximately: frame 190) rather than the one identified as masculine (frame 115), it seems prudent to consider the possibility that peri-ovulatory shifts in attractiveness ratings might result from an increased interest in the perceived sexual characteristics of the depicted male rather than in his masculinity per se.
Blue Jeans photo courtesy of Hendrike, 2005. Wikipedia Commons.
Johnston, V. (2001). Male facial attractiveness: evidence for hormone-mediated adaptive design Evolution and Human Behavior, 22 (4), 251-267 DOI: 10.1016/S1090-5138(01)00066-6
Tarin, J. (2002). Do women have a hidden heat period? Human Reproduction, 17 (9), 2243-2248 DOI: 10.1093/humrep/17.9.2243
Wilcox, A. (2004). On the frequency of intercourse around ovulation: evidence for biological influences Human Reproduction, 19 (7), 1539-1543 DOI: 10.1093/humrep/deh305
About two years ago, Elliot & Niesta (2008), concluded that the color red makes men find women more attractive. Essentially, they found that men – but not women – rated black and white photos of women about a point higher in physical attractiveness (on a 9-point scale) when the photos were presented on a red background than when presented on a white/gray/green background. They also found a similar result when the woman’s shirt was red rather than blue in a color photograph. The authors favor a sexual-signalling interpretation of these results: that men key into displays of red in women due to the color’s role in signaling sexual health/availability/interest/arousal (they do acknowledge, however, that other – more culturally influenced – explanations for this data are possible). The implication is that red enhances attractiveness (the photos used reasonably attractive subjects) – not by an intrinsic characteristic of the stimulus like symmetry or averageness – but by somehow covertly activating sexual cognition in men. I have been unable to find a replication of this research in the subsequent literature. After two years, this lack of replication or direct follow-up on a variable with this much potential impact on attractiveness ratings is concerning.
I am aware of one subsequent study that relates the color red to attractiveness indirectly: Stephen, et.al. (2009) have found that the color “blood red” makes faces appear healthier (apparently, no direct rating of attractiveness was used in this study). Other psychology of color studies have been and continue to be published: with no clear application to beauty research. For example, using a Stroop-like methodology, Moller et.al. (2009) found that the color red is implicitly associated with failure and negativity – a relationship that is difficult to mesh with the Elliot & Niesta data.
The photo of Daniela Niesta (below) is available from the University of Rochester website:
It is possible to download a full-size version of the image from this page. If you do, I urge you to look at the images displayed in this photo. They are examples of the stimuli used in experiment five. To my eye, on my color calibrated monitor, the skin tone in the image with the red shirt is more pleasing. This is likely due to a contrast effect, as only the colors of the shirt were manipulated by the experimenters. This, of course, suggests a competing explanation for the data (at least of experiment five).
All-in-all, a cautious acknowledgment of the conclusions reached in the Elliot & Niesta study is called for, pending replication and clarification in further research.
Photo of J.W.Waterhouse’s Lady of Shalott courtesy of Wikipedia Commons.
Photo of Daniela Niesta courtesy of the University of Rochester.
Elliot, A., & Niesta, D. (2008). Romantic red: Red enhances men’s attraction to women. Journal of Personality and Social Psychology, 95 (5), 1150-1164 DOI: 10.1037/0022-35220.127.116.110
Moller, A., Elliot, A., & Maier, M. (2009). Basic hue-meaning associations. Emotion, 9 (6), 898-902 DOI: 10.1037/a0017811
Stephen, I., Coetzee, V., Law Smith, M., & Perrett, D. (2009). Skin Blood Perfusion and Oxygenation Colour Affect Perceived Human Health PLoS ONE, 4 (4) DOI: 10.1371/journal.pone.0005083
Piers Cornelissen has offered some pointed objections to concluding that WHR (waist-hip ratio) is more important than BMI (body mass index) in the evaluation of women’s body attractiveness. He posted these objections as a response to Caution: Curves Ahead. Since comments are easily overlooked on this blog due to the nature of the site’s formatting, I have decided to highlight his argument by reproducing it here.
A few points regarding Caution: Curves Ahead
1) BMI and WHR range effects.
Smith et al. (Smith, K.L., Cornelissen, P.L. & Tovée, M.J. (2007) Colour 3D Bodies and Judgements of Human Female Attractiveness. Evolution and Human Behaviour, 28, 48-54) used colour videos of women, who were rotated twice through 360 deg, as stimuli in an attractiveness rating paradigm. The relative range for WHR and BMI in these stimuli can be described by looking at the range of their z-scores: -2.55 to 2.72 and -1.70 to 1.89 respectively. In other words, there was more variability in WHR than BMI. However, the correlations between attractiveness and WHR / BMI in this study were -0.28 (p=0.06) and -0.73 (p<0.0001) respectively.
A similar result was reported in Tovee et al. (Tovée, M.J., Warren, T.T.L., Hancock, P. & Cornelissen, P.L. (2002). Visual cues to female attractiveness: Waveform analysis of body shape. Proceedings of The Royal Society, B Vol. 269, No. 1506., 2205-2213). In this study, using 2D gray level images in front view, stimuli were picked deliberately so that the WHR range outweighed the BMI range by a factor of ~3.
In conclusion, using videos / photos of whole bodies, we have repeatedly found that we can’t get WHR to work in explaining attractiveness ratings even when it has a bigger relative range than BMI.
2) False positives.
If Caucasian males were to rely primarily on WHR for mate choice when judging the bodies of potential partners, they would be prone to making false positive errors; sometimes they would pick women with amenorrhoea as partners who are infertile. As Fig. 1 shows in Tovee et al. (Tovée, M.J. and Cornelissen, P.L. (1999) Visual cues to female physical attractiveness. Proceedings of the Royal Society of London Series B-Biological Sciences, 266(1415), 211-218), it is perfectly possible to find individual females with optimally attractive WHRs but who have extremely low body fat, and who have amenorrhoea as a consequence. So, it is hard to see how WHR alone can be treated as a reliable signal.
3) Micrograft surgery BMI / WHR manipulations.
Clearly this is an elegant paradigm in principle. Indeed, based on their Fig. 2A, I would be hard pushed *not* to agree that the post-operative figures in Dixson et al. are more attractive (Dixson, B., Sagata, K., Linklater, W., & Dixson, A. (2009). Male preferences for female waist-to-hip ratio and body mass index in the highlands of Papua New Guinea American Journal of Physical Anthropology DOI: 10.1002/ajpa.21181). However, my reason for this decision would have to include the fact that the post-operative images are aesthetically more pleasing because they are rounder and smoother. This image property was neither quantified nor coded qualitatively in any way, and no such measures were included in the analyses either as outcome variables or covariates. Moreover, from an image analysis point of view, a smoothness metric could be obtained without having anything to do with WHR. Therefore, it would be useful to check that roundness / smoothness is not a confound in future research of this kind.
Secondly, even if the conclusion from these experiments is correct, we still have to explain why WHR fails as a cue when photos/videos of the *whole* body are available. Are we really suggesting that the answer lies in males *only* making their mate selection choice when they have a close up view – because that is the implication.
Many contemporary beauty researchers assume/conclude that attractive, sexually dimorphic features in men (strong jaws, increased lean muscle mass, etc.) are true signals of mate quality. This model is best illustrated in peacock tail feathers: the size and color of the train makes the male more sexually attractive to peahens. Rather than being just an attractive, but functionally useless ornament, this weighty handicap is an honest signal to peahens of the male’s quality – because this tail is so costly to possess. Any peacock that can thrive with this large disadvantage must be well-adapted – that is, possess good genes.
Testosterone inhibits immune functioning. Given this, the basic argument is that any potential mate with testosterone-related features must have “good genes” in order to thrive with the testosterone handicap. One big problem with the testosterone as a handicap hypothesis is that testosterone is not merely an immunity suppressant. Testosterone produces benefits as well:
The primary fitness benefits of testosterone are multifaceted, including support for optimal spermatogenesis, the development and maintenance of secondary sexual characteristics that augment male competitiveness and attractiveness, as well as libido. Other associations include competitive ability and possible relationships with social dominance. (Bribiescas & Ellison, p. 104)
Thus, testosterone’s effects involve trade-offs: there are pros and cons to having testosterone coursing through one’s veins.
The second big problem with this hypothesis is that there is no evidence for this phenomenon in mammals. Roberts, et.al. (2004) found evidence for the immunocompetence handicap hypothesis (what I am calling the testosterone as handicap hypothesis) in birds and reptiles, but not mammals. Nunn, et.al. (2008) subsequently corroborated this conclusion with regard to mammals.
Arguments which assume sexually attractive, dimorphic features in human males are costly handicaps – and thus true signals – are overlooking the complex influence of testosterone in human adaptations as well as overlooking the lack of evidence for applying this concept to mammals generally and humans specifically.
Image courtesy of Rhodney Carter, Wikipedia Commons.
Nunn, C., Lindenfors, P., Pursall, E., & Rolff, J. (2009). On sexual dimorphism in immune function Philosophical Transactions of the Royal Society B: Biological Sciences, 364 (1513), 61-69 DOI: 10.1098/rstb.2008.0148
ROBERTS, M., BUCHANAN, K.L., & EVANS, M.R. (2004). Testing the immunocompetence handicap hypothesis: a review of the evidence Animal Behaviour, 68 (2), 227-239 DOI: 10.1016/j.anbehav.2004.05.001