  The polyvagal theory (PT), offered by Porges (2021), proposes that the
autonomic nervous system (ANS) was repurposed in mammals, via a second vagal
nerve, to suppress defensive strategies and support the expression of
sociality. Three critical assumptions of this theory are that (1) the
transition of the ANS was associated with the evolution of social mammals from
asocial reptiles; (2) the transition enabled mammals, unlike their reptilian
ancestors, to derive a biological benefit from social interactions; and (3) the
transition forces a less parsimonious explanation (convergence) for the
evolution of social behavior in birds and mammals, since birds evolved from a
reptilian lineage. Two recently published reviews, however, provided compelling
evidence that the social asocial dichotomy is overly simplistic, neglects the
diversity of vertebrate social systems, impedes our understanding of the
evolution of social behavior, and perpetuates the erroneous belief that one
group, non-avian reptiles, is incapable of complex social behavior. In the
worst case, if PT depends upon a transition from asocial reptiles to social
mammals, then the ability of PT to explain the evolution of the mammalian ANS
is highly questionable. A great number of social behaviors occur in both
reptiles and mammals. In the best case, PT has misused the terms social and
asocial. Even here, however, the theory would still need to identify a
particular suite of behaviors found in mammals and not reptiles that could be
associated with, or explain, the transition of the ANS, and then replace the
asocial and social labels with more specific descriptors.
