Women and men are different. This sentence can be considered trivial in scientific terms, since differences between females and males are the core point of sexual reproduction as a highly successful system fixed by natural selection during the evolution of many animals and plants, humans included.

 A different question is the psychological translation of the need for differences when gender is implied. Obviously, psychological differences are of great importance when it comes choosing a mate. Many scientific achievements point to attractiveness, beauty and reward as key aspects of the subject's preferences for faces of people of the opposite sex. However, little was known on the differences existing between the cerebral mechanisms underlying the perception of beauty in women and men. Until a new neurocognitive science, neuroaesthetics, come to light.

The empirical field of neuroaesthetics started in 2004, when three different studies offered the first accounts of the activation of brain areas during aesthetic appreciation (Cela-Conde et al, 2004; Kawabata & Zeki, 2004; Vartanian & Goel, 2004). None of them checked out what differences between males and females’ activation of the brain in aesthetic tasks exist. Cinzia di Dio and Vittorio Gallese (2009) reviewed five years later the state-of-the-art of neuroaesthetics, recommending 29 works. None of them referred to sex differences in the appreciation of beauty either, with the exception of our study being here commented (Cela-Conde et al, 2009). It was qualified by di Dio and Gallese as “a pioneer work in the neural exploration of gender-related differences in the appreciation of artworks. The use of magnetoencephalography (MEG) allows to study the various temporal stages at which stimuli are processed. Through this technique, it was possible to pinpoint fine gender-differences in parietal regions, which are then discussed by the authors from an evolutionary perspective.”

Before entering in such work, let’s consider a research not mentioned by di Dio and Gallese (2009) though having some relationship with the perception of beauty. James Schirillo (2007) carried out an experiment on the emotional expression displayed by artistic portraits painted by Rembrandt. in Western Europe art from the sixteenth to the twentieth century, ∼68% of the women were painted with their left-cheek exposed while only ∼56% of the men exposed their left-cheek.

 Rembrandt followed this pattern—64% of his female portraits the left-cheek faces the viewer. Schirillo (2007) stated that “This asymmetry is consistent with viewers rating Rembrandt’s left-cheeked male portraits as likely to be avoided, which may reflect that aggressive displays of dominance are governed by the contralateral right-hemisphere, while rating left-cheeked female faces as likely to be approached may indicate sexual attractiveness.“ However, Schirillo did not register any brain activity in his subjects, being his experiment based on semantic judgments. So the question is: does any difference exist between females and males when viewing and rating the beauty of objects?

An experiment carried out by our research group (Cela-Conde et al, 2009) compared by means of magnetoencephalography (MEG)—a technique that detects changes in the magnetic fields generated by the postsynaptic activity of neurons with a temporal resolution of milliseconds— brain activity in 10 female and 10 male participants while rating the beauty of artistic and non-artistic visual stimuli. We seek to ascertain whether any possible differences between the sexes are due to evolutionary processes that occurred along the evolution of the human lineage or in an earlier primate ancestor. If gender-related differences would be identified in relatively conserved brain regions, it is possible that they were inherited from our primate ancestors. If, conversely, differences between men and women appear in brain regions known to have undergone considerable modifications after the human and chimpanzee lineages split, it is likely that they are due to evolutionary processes that were especially relevant to the human way of life.

 Our experiment revealed that visual aesthetic appreciation involves high-level cognitive activity, both in women and men. The main focus of activity in both sexes is in the parietal lobe. The parietal activity is bilateral in the case of women but lateralized to the right hemisphere in the case of men. The gender-related differences in the neural correlates of the aforementioned cognitive activity indicate that there might be different processing strategies for beauty in women and men. Specifying these differential strategies is not easy to ascertain.

As we argued, a possible explanation for the greater lateralization in men than in women could be grounded on differences between exploration strategies. Women would carry out an exploration of categorical spatial relations. The processes occurring in the right hemisphere of male participants suggest an exploration strategy based on coordinate spatial relations. However, there are other alternatives to the interpretation based on spatial exploration strategies. It is generally accepted that the right parietal cortex is associated with global visual attention and the left with local attention. Perhaps women make use of both global and local features in making their judgments, whereas men only rely on global features. Another hypothesis could link our observations to language. Women obtain higher scores on a diversity of verbal and language tasks (Hyde & Linn, 1988) Perhaps women are more likely to associate the images with verbal labels than men, producing the lateralizing differences in neural activity. This hypothesis deserves further experimental work before seriously being taken into consideration. Even though the specific cognitive processes related with the appreciation of beauty are still to be determined, we propose an explanation for the evolutionary features of such capacity related with sexual selection. Silverman’s and Eals’s (1992) hunter-gatherer hypothesis of gender differences in spatial abilities provides the most convincing scenario. Differences in spatial ability between men and women would be associated with the division of labor between the sexes in hunting and gathering. In any case, given that parietal spatial-processing streams show certain derived traits present only in our species, it seems quite probable that gender-related differences in this pathway appeared after the human and chimpanzee lineages split.

Most gender differences identified in our study correspond to parietal regions. In the genus Homo, parietal development leading to brain globularity has been described by palaeoneurologists as a ‘‘modern pattern,’’ characteristic of Homo sapiens (Bruner et al, 2003, 2004). Thus, in spite of the appreciation of Homo neanderthalensis for decorative objects (Zilhao et al, 2010, for instance), the modern way to engage brain activity in the appreciation of beauty seems to be characteristic exclusive of our species.

References:

Bruner, E., Manzi, G., & Arsuaga, J. L. (2003). Encephalization and allometric trajectories in the genus Homo: Evidence from the Neandertal and modern lineages. Proceedings of the National Academy of Sciences, 100, 15335-15340. 

Bruner, E. (2004). Geometric morphometrics and paleoneurology: brain shape evolution in the genus Homo. Journal of Human Evolution, 47, 279-303.

Cela-Conde, C. J., Ayala, F. J., Munar, E., Maestú, F., Nadal, M., Capó, M. A., . . . Marty, G. (2009). Sex-related similarities and differences in the neural correlates of beauty. Proceedings of the National Academy of Sciences, USA, 106, 3847-3852.

Cela-Conde, C. J., Marty, G., Maestú, F., Ortiz, T., Munar, E., Fernández, A., . . . Quesney, F. (2004). Activation of the prefrontal cortex in the human visual aesthetic perception. Proceedings of the National Academy of Sciences USA, 101, 6321–6325.

Di Dio, C., & Gallese, V. (2009). Neuroaesthetics: A review. Current Opinion in Neurobiology, 19, 1-6.

Hyde, J.S. & Linn, M.C. (1988) Gender differences in verbal ability: A meta-analysis. Psychol Bull, 104, 53–69.

Kawabata, H., & Zeki, S. (2004). Neural Correlates of Beauty. Journal of Neurophysiology, 91, 1699-1705.

Schirillo, J. A. (2007). Gender’s effect on the hemispheric laterality of Rembrandt’s portraits. Spatial Vision, 21(1-2), 19-26.

Silverman, I., & Eals, M. (1992). Sex differences in spatial abilities: Evolutionary theory and data. In J. Barkow, L. Cosmides & J. Tooby (Eds.), The Adapted Mind (pp. 487-503). New York, NY: Oxford University Press.

Vartanian, O., & Goel, V. (2004). Neuroanatomical correlates of aesthetic preference for paintings. Neuroreport, 15, 893-897.  

Zilhão, J., Angelucci, D. E., Badal-García, E., d'Errico, F., Daniel, F., Dayet, L., . . . Zapata, J. (2010). Symbolic use of marine shells and mineral pigments by Iberian Neandertals. Proceedings of the National Academy of Sciences, USA, 107, 1023-1028. doi: 10.1073/pnas.0914088107