It is clear that genes at the major histocompatibility complex (MHC) are involved in mate preferences in a range of species, including humans. However, many questions remain regarding the MHC's exact influence on mate preference in humans. Some research suggests that genetic dissimilarity and individual genetic diversity (heterozygosity) at the MHC influence mate preferences, but the evidence is often inconsistent across studies. In addition, it is not known whether apparent preferences for MHC dissimilarity are specific to the MHC or reflect a more general preference for genome-wide dissimilarity, and whether MHC-related preferences are dependent on the context of mate choice (e.g., when choosing a short-term and long-term partner). Here, we investigated whether preferences for genetic dissimilarity are specific to the MHC and also whether preferences for genetic dissimilarity and diversity are context dependent. Genetic dissimilarity (number of alleles shared) influenced male, but not female, partner preferences, with males showing a preference for the faces of MHC-dissimilar females in both mating contexts. Genetic diversity [heterozygosity (H) and standardized mean (d2)] influenced both male and female preferences, regardless of mating context. Females preferred males with greater diversity at MHC loci (H) and males preferred females with greater diversity at non-MHC loci (d2) in both contexts. Importantly, these findings provide further support for a special role of the MHC in human sexual selection and suggest that male and female mate preferences may work together to potentially enhance both male and female reproductive success by increasing genetic diversity in offspring.
The major histocompatibility complex (MHC, or human leukocyte antigen, HLA, in humans) is found in all jawed vertebrates and contains genes that are implicated in many important biological functions, including immune functioning (Doherty and Zinkernagel, 1975 and Lechler and Warrens, 2000) and mate preferences (reviewed in Havlicek and Roberts, 2009 and Milinski, 2006). Because MHC genes are important for several aspects of individual fitness, they are particularly good candidates for studying the genetic benefits of mate choice (Apanius et al., 1997, Schwensow et al., 2008 and Tregenza and Wedell, 2000). MHC genes are directly involved in immune functioning, where each allele codes for peptides that can detect a restricted range of antigens derived from pathogens and parasites. MHC alleles are expressed codominantly. Therefore, increased allelic diversity at the MHC should be beneficial as it broadens the range of antigens an individual can detect and present to T cells for destruction (Doherty & Zinkernagel, 1975). There is evidence that greater MHC diversity (heterozygosity) enhances immunocompetence in some cases (e.g., Carrington et al., 1999, Duggal et al., 2004, Froeschke and Sommer, 2005, Hraber et al., 2007, McClelland et al., 2003, Oliver et al., 2009, Schwensow et al., 2007 and Thursz et al., 1997), although not in all (e.g., Hill et al., 1991 and Meyer-Lucht and Sommer, 2005).
