How do we choose our mates? Some scientists have suspected that it is not for looks or fashion or love but rather, genes.

A new study provides support for this idea by looking at lemurs in Madagaskar. Female fat-tailed dwarf lemurs (Cheirogaleus medius) live in life-long pairs, yet notoriously cheat on their partners to improve the genetic fitness of their offspring.

The team headed by Prof. Simone Sommer looked for possible genetic benefits in the obligate pair-living fat-tailed dwarf lemur which maintains life-long pair bonds but has an extremely high rate of extra-pair paternity. Possible mechanisms of female mate choice were investigated by analyzing overall genetic variability as well as a marker of adaptive significance (major histocompatibility complex, MHC-DRB exon 2). MHC-genes determine not only the individual’s immune response but also the individual’s body odor. This holds true for animals as well as for humans.

"I'm not a tramp, I'm cheating on you for evolution" Picture by Simone Sommer

The study indicated that females preferred males both as social and as genetic fathers for their offspring if they have a higher number of MHC-alleles and MHC-supertypes, a lower overlap with the female’s MHC-supertypes as well as a higher genome-wide heterozygosity than randomly assigned males. This means that females looked for the most genetically different males preferably with a “healthy” set of genes. Mutual relatedness had no influence on mate choice.

Interestingly, females were most likely to cheat on their social partner if he had a higher overlap with the female’s MHC supertype. Extra-pair mates were chosen mostly for their genetic difference, thus maximising the genetic complementarity of sires to the females.

Article: Nina Schwensow et al.: MHC-associated mating strategies and the importance of overall genetic diversity in an obligate pair-living primate (in Evolutionary Ecology; DOI 10.1007/s10682-007-9186-4)