This week, we decided to take a look at the genetic basis for some of the theories revolving around attractiveness that we’ve been discussing. The 2004 study we chose focuses on the theory that the reason one person is attracted has its basis in the immune system. It is well established that disease has been a huge factor in the evolutionary trajectory of humans – ask any high school biology teacher about Sickle-Cell Anemia, for example. One of the great innovations of sexual reproduction has been the ability to mix and match antigens on the cell surface, where pathogens like viruses bind to do their damage. The genomic region responsible for these antigens is called the major histocompatability complex (MHC), an extremely large and varied family of genes. The theory that has been percolating for years now is that you will be attracted to someone’s scent if they have different, or complimentary, MHC alleles. Besides the quantity of good evidence in support of this theory, I think it’s rather romantic.
day-amn, you got some fine alpha-helices.
These researchers’ approach was to see if the MHC had any bearing on facial attractiveness, as well. They used women to judge the attractiveness of men’s faces and judge the health of magnified pictures of the facial skin of these men. To control for racial preference, they used all white men. Avery noticed that they did not seem to mention controlling for female preference by choosing only straight women. However, this arguably shouldn’t be a large issue, because everyone can gauge what she thinks is the standard for attractive whether or not they are personally attractive. The findings were pretty cool: more homozygous men (with fewer variation of alleles at the 3 chosen loci) did definitively worse than heterozygous men on both attractiveness and skin health. When comparing alleles shared between the women and the male subjects, the most attractive men who either had the most or the least in common with the women choosing. However, the researchers contended that this was because some women preferred men with MHCs similar to theirs, while others preferred those who were different. I invite you to discuss with me why this might be.
Could MHC homozygosity just be an indicator of poor genetic quality as a result of things like inbreeding? Almost definitely not – other studies have shown that heterozygosity of MHC has no demonstrated correlation with the degree of heterozygosity at other key sites in the genome. This raised a question, though: would degree of inbreeding elicit the same pattern of female preference that degree of MHC homozygosity did in this study? The logistics of finding volunteers with a varied enough degree of inbreeding without bias would be a challenge. Also, though female choice is the canonical example of intersexual selection, it would be worth doing the same with rating the attractiveness of women and see if the patterns change at all.
Roberts, S. Craig et al. “MHC-heterozygosity and human facial attractiveness.” Evolution and Human Behavior. 26(2005) 213 – 226
