BODY ODOR PREFERENCES IN MEN AND WOMEN - DO THEY AIM FOR SPECIFIC MHCCOMBINATIONS OR SIMPLY HETEROZYGOSITY

The major histocompatibility complex (MHC) is an immunologically impor tant group of genes that appears to be under natural as well as sexual selection. Several hypotheses suggest that certain MHC-allele combina tions (usually heterozygous ones) are superior under selective pressur e by pathogens. This could influence mate choice in a way that prefere nces function to create MHC-heterozygous offspring, or that they funct ion to create specific allele combinations that are beneficial under t he current environmental conditions through their complementary or epi static effects. To test these hypotheses, we asked 121 men and women t o score the odours of six T-shirts, worn by two women and four men. Th eir scorings of pleasantness correlated negatively with the degree of MHC similarity between smeller and T-shirt-wearer in men and women who were not using the contraceptive pill (but not in Pill-users). Depend ing on the T-shirt-wearer the amount of variance in the scorings of od our pleasantness that was explained by the degree of MHC similarity (r (2)) varied between nearly 0 and 23%. There was no apparent effect of gender in this correlation: the highest r(2) was actually reached with one of the male odours sniffed by male smellers. Men and women who we re reminded of their own mate/ex-mate when sniffing a T-shirt had sign ificantly fewer MHC-alleles in common with this T-shirt-wearer than ex pected by chance. This suggests that the MHC or linked genes influence human mate choice. We found no significant effect when we tested for an influence of the MHC on odour preferences after the degree of simil arity between T-shirt-wearer and smeller was statistically controlled for. This suggests that in our study populations the MHC influences bo dy odour preferences mainly, if not exclusively, by the degree of simi larity or dissimilarity. The observed preferences would increase heter ozygosity in the progeny. They do not seem to aim for more specific MH C combinations.