In the absence of lifetime monogamy, males and females have conflicting interests over the amount of maternal investment in offspring, with males favouring more maternal investment than is optimal for the female. In polygynous species, males copulate with several females that may later breed communally. Thus, offspring in a communal nest will be more closely related through the paternal than the maternal line. It may therefore be in the male's interest that all of his offspring are nursed regardless of their maternal origin. This may have selected for paternally expressed genes that suppress kin recognition during lactation.