for the scent of men with high facial symmetry correlated with their probability of conception. Men's body odor is also affected by their diet, with women expressing preferences for male body odor associated with increased dietary fruit and vegetable and protein content, and reduced carbohydrate content. Genetics Studies have explored the genetic basis behind such issues as facial symmetry and body scent and how they influence physical attraction. In one study in which women wore men's T-shirts, researchers found that women were more attracted to the bodily scents in shirts of men who had a different type of gene section within the DNA called major histocompatibility complex (MHC). MHC is a large gene area within the DNA of vertebrates which encodes proteins dealing with the immune system and which influences individual bodily odors. One hypothesis is that humans are naturally attracted by the sense of smell and taste to others with dissimilar MHC sections, perhaps to avoid subsequent inbreeding while increasing the genetic diversity of offspring. Furthermore, there are studies showing that women's natural attraction for men with dissimilar immune profiles can be distorted with use of birth control pills. Other research findings involving the genetic foundations of attraction suggest that MHC heterozygosity positively correlates with male facial attractiveness. Women judge the faces of men who are heterozygous at all three MHC loci to be more attractive than the faces of men who are homozygous at one or more of these loci. Additionally, a second experiment with genotyped women raters, found these preferences were independent of the degree of MHC similarity between the men and the female rater. With MHC heterozygosity independently seen as a genetic advantage, the results suggest that facial attractiveness in men may be a measure of genetic quality. General genetic heterozygosity has been demonstrated to be related to attractiveness in that people with mixed genetic backgrounds (i.e., mixed race people) as seen as more attractive than people with a more similar genetic parents. (i.e., single race people). However, some studies have not found that mixed race individuals are rated as more attractive, and one found that only certain mixes were rated as more attractive; this study argued that equating race with genetics was incorrect and argued for social influences as the cause. Youthfulness A 2010 OkCupid study on 200,000 of its male and female dating site users found that women are, except those during their early