Figure 1. Parrot feather colorations are signs of attractiveness (Photos: Creative Commons).
What makes a person’s face attractive? Is attractiveness determined by cultural preferences, or is attractiveness simply a process explained by Darwinian evolution? To answer these questions, Dartmouth College’s Seth Dobson and Zaneta Thayer at Northwestern University, along with other researchers, are trying to determine whether particular facial features are universally accepted as attractive across human populations (1, 2).
To study what physical features are considered attractive, some biologists have looked at animals for clues (3). For example, the traits of peacocks and the coloration of parrots, both examples of sexual dimorphism, represent examples of the inheritance of sexual characteristics based on genetic material (Figure 1). Similarly, studying the physical traits of people, researchers have postulated that evolution has led to human biases about attractiveness that operate independently of a person’s cultural upbringing (2, 4). Both approaches represent the Darwinian explanation for attractiveness, which holds that the process of sexual selection results in phenotypes, such as facial features, that provide an advantage for individuals competing to find mates (5). In contrast, the non-Darwinian view holds that attractiveness is something learned within a particular culture and may vary between different cultures.
Figure 2. A Peacock’s fanned out tail feathers entail male dominance and are designed to capture the females’ attention (Photo: Creative Commons)
Professor Dobson’s work on attractiveness focuses on the universal facial attractiveness (UFA) theory which postulates that all human beings find certain facial characteristics attractive because they are predictors of qualities that make good mates. More simply, some physical features are preferred across cultures because they represent signs of mate quality (2). According to Dobson and Thayer, the UFA theory predicts that if facial features are attractive independent of culture and geography, and attractiveness helps determine reproductive success, then sexual selection would lead to those features expressed at similar rates across different cultures and across distant geographies (2). Thus, if facial symmetry were a reliable predictor of attractiveness, and led to success in breeding, similar measures of facial symmetry would be found across cultures and among individuals living at different locations around the world.
To study attractiveness, Dobson and Thayer focused on the shape of a person’s chin, normally considered to be a sign of attractiveness among humans, and a feature specific only to humans (2). Dobson and Thayer predicted that if people from distant geographies had similar chin shapes, as predicted by the UFA hypothesis, and if mating preferences influenced morphological evolution of facial features, as implied by sexual selection theory, then the geographic variation in chin shape would be small (2).
To test this hypothesis, Dobson and Thayer observed the variation in chin shapes among 180 healthy male and female skeletons collected from the mandibular specimens contained at the American Museum of Natural History in New York (2). To obtain a sample from different geographical areas, they selected skeletons’ jawbones from Australia, Africa, Asia, and Europe, which were then scanned and digitized. With the digitized data, Dobson and Thayer used a “morphometric technique” to quantify chin shapes using elliptical Fourier functions analysis, a technique for analyzing outlines by fitting trigonometric, polynomial, or spline functions to a particular shape (2, 6).
Figure 3. Example of “generic” chin/face shapes (Images: Creative Commons)
Again, the UFA theory predicted that based on Darwinian evolution, humans across different cultures and geographies would find certain chin geometries to be attractive, and thus such traits would be prevalent in populations separated by geography. However, in contrast to the predictions of the UFA theory, Dobson and Thayer found that the average Eastern European chin was not the average West Asian chin which was not the average South African chin (2). That is, inter-region variability was shown. Thus, the data analyzed by Dobson and Thayer provides evidence disputing the UFA theory. As suggested by Yu and Shepard a person’s physical attractiveness may be less important in finding a mate than cultural factors (7). So will the shape of your chin determine your success at finding a mate? According to Dobson and Thayer, the answer is no.
References
1. H. H., Anyaso, (2013), All Chins are Not Created Equal, Available at http://www.eurekalert.org/pub_releases/2013-04/nu-aca041213.php (19 April 2013).
2. Z. M., Thayer, and S. D., Dobson, (2013), Geographic Variation in Chin Shape Challenges the Universal Facial Attractiveness Hypothesis, PloS ONE, 8 (4): doi:10.1371/journal.pone,0060681.
3. K., Grammer, B., Fink, A. P., Møller, and R., Thornhill, (2003), Darwinian Aesthetics: Sexual Selection and the Biology of Beauty, Biological Reviews, 78: 385–407.
4. D. Bennett, Universal Attractiveness and the Meaning of Our Chins, Available at http://www.businessweek.com/articles/2013-04-12/universal-attractiveness-and-the-meaning-of-our-chins (17 April 2013).
5. B. C., Jones, A. C., Little, B. P., Tiddeman, D. M., Burt, and D. I., Perrett, (2001), Facial Symmetry and Judgments of Apparent Health Support for a “Good Genes” Explanation of the Attractiveness and Symmetry Relationship, Evolution and Human Behavior, 22, 417–429.
6. P. E., Lestrel, editor, (1997), Fourier Descriptors and their Applications in Biology, Cambridge: Cambridge University Press.
7. D. W., Yu, and G. H., Shepard, (1998), Is Beauty in the Eye of the Beholder? Nature, 396: 321–322.