Over the past 20 years, long-term studies have shown that mammalian fa
thers, brothers and even unrelated males may contribute substantially
to the care of the young. Recently, more field studies of mammals with
male care have further expanded interest in male care potential. Male
mammals can never be sole care-givers because offspring depend on mat
ernal milk, but assistance provided by males may allow females to prod
uce more energetically costly litters. The need for such male care con
tributes to the development of obligate social monogamy or communal br
eeding.