Families of husband and wife are commonly considered to be the fundamental social group in society. However, recent research indicates that primate sociality did not evolve from smaller to larger groups of adults. Primates species seem to have shifted from solitary living to living in groups with multiple male adults and multiple female adults. Some species then shifted to one-adult-male/multiple-adult-female groups, and others shifted to one-adult-male/one-adult-female pair-bonded groups. Hence, from an evolutionary perspective, large-group sociality was the fundamental form of sociality in primate evolution.
Humans typically form pair bonds among breeding adults, but these pair bonds are embedded within large groups of multiple adult males and adult females. That human pattern of sociality is distinctive among mammals. Concern about poor-quality sociality in humans tends to link family breakdown to wider social disorder. An evolutionary perspective highlights that poorly structured large-group sociality affects family formation.
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Study:
Shultz, Susanne, Christopher Opie, and Quentin D. Atkinson. 2011. “Stepwise evolution of stable sociality in primates.” Nature. 479 (7372): 219-222. (review article)