Evolutionary anthropology has a long history of contributing to our understanding of how humans establish and maintain relationships, a central area of research in the study of human evolution. Social relationships have a positive effect on health, survival, and reproduction. Of particular importance in understanding the evolution of parenting relationships is to understand male paternal care (i.e. fatherhood). We find fascinating examples of fatherhood in titis and owl monkeys of South America where we see a commitment of males to the care of infants that is unparalleled by any other mammal, sometimes helping even more than the mother. Why is this? What does it mean? These species offer us a "two care-givers" model to explore the potential role of parenting strategies in the evolution of human and nonhuman primate societies. They can help us identify behaviors that facilitate the development of strong, healthy bonds between fathers and young.