Family relationships are a key component of human evolution. The extent and duration of offspring care are extraordinary and unique in the huge informational transfer via language. Human kin relationships are bilateral, complex, variable, multigenerational, and intergroup. Mating relationships are also variable and often strongly influenced by kin in traditional cultures. These aspects of our sociality are biologically embedded in neurological and physiological mechanisms. Here we examine how hormonal and neural mechanisms provide clues to the evolution of the emotional and cognitive systems that underpin human family psychology.