What makes male mice paternal?

Both copulation and postcopulatory cohabitation with pregnant females reduce infanticide and enhance paternal responsiveness in male CS1 mice. The effectiveness of copulation in this process, however, depends on the number of occasions that males have previously encountered infants. Infanticidal males which have been subordinated in brief encounters with other males are less likely to commit infanticide in subsequent tests than are those which became dominant to other males. Males which copulate and cohabit with a relatively large female are less likely to be infanticidal than are those with a relatively small female. These data suggest that males are subordinated after copulation by their mates and that this subordination is a factor in the reduction of infanticide and the initiation of paternal responsiveness.