Mice use their sense of smell to detect and avoid mating with relatives

To prevent the accumulation of harmful recessive mutations, many animals have evolved complex mechanisms for kin discrimination. Mice, for instance, use their sense of smell to detect Major Histocompatibility Complex (MHC) molecules in the urine of others. By choosing mates with an MHC profile different from their own, they ensure their offspring have a more robust immune system and avoid the biological 'inbreeding depression' caused by mating with close relatives.