[throwaway769879]

Preferences evolve during the lifetime of humans. Preferences in infants is usually different from preferences in sexual partners. Don't have the source handy, but it has been shown that females look for people with different genes (at least in regards to antibody-encoding) for mating, but once pregnant, seek people with similar genes (e.g. family). In general, most studies saying people prefer sexual partners with different genes refer to the genes encoding antibodies, not the genome in general.