Only dominant pygmy females reproduce; their presence suppresses the release of these in other females
Marmosets may 
leave their natal groups when they become adults, in contrast to other primate... [DOC] [TLE] Mothers and Others: the evolutionary origins of mutual understanding [PAR] [And, our] ability to identify with others and vicariously experience their ... [and] 
serves humans well in all sorts of social circumstances, not just in acts of .... Part 
of the explanation for the evolution of alloparental care is that these .... infants - 
even if human groupings don't limit reproduction to the dominant female (see 
below).