One explanation for the
similarities between dogs and
humans is that the two species may have evolved under similar pressures that favored «survival of the friendliest,»
with benefits and rewards for more cooperative social
behavior.
Juxtaposing descriptions of social
behaviors of
humans with those of other primates, Maestripieri emphasizes our
similarities with our closest evolutionary relatives.
Two major reasons for this view are (1) the strong
similarities between monkeys and
humans in social
behavior, endocrine function, brain structure, and degree and duration of mother - infant nurturance (Harlow and Zimmerman 1959; Kalin and Shelton 2003; Mendoza and Mason 1997), or, in the unique case of titi monkeys, the extent of biparental care (Hennessy 1997); and (2) the extent to which monkeys fulfill Ainsworth's criteria of attachment (Ainsworth 1972), namely, unequivocal distress upon complete separation from the attachment figure and alleviation of this distress (both behavioral and physiological) upon reunion / interaction
with the attachment figure (Mendoza and Mason 1997).