Rhythmic Behavior, is ever-present in, and an essential feature of, all interpersonal interactions wherein pulse is used as a temporal framework for interaction. Although rarely recognized as such, it is one of the defining features of modern-day humans, enabling the socially rooted behaviors (and corresponding concepts and emotions) that are so distinct to our species. We cannot, as yet, be sure that we are unique among higher mammals in having evolved pulse-driven rhythmic abilities. However, we can confidently state that there is, at least, something unique in the contexts in which rhythmic behaviors are employed, the exact nature and level of our abilities, and the extent to which rhythmic abilities are displayed in humans. Evidence to date suggests that, even if some quasi-rhythmic ability is present in other primate species, the capacity and/or motivation for entraining actions to external pulsed stimuli is not. This, together with recent ontogenetic evidence (McAuley & Riess-Jones, in press), suggests to us that the use of pulse as a means of building expectancies and providing a mutually contingent temporal framework for interpersonal interactions precedes more overtly action-perception coupled capacities both ontogenetically and phylogenetically. We argue that understanding interpersonal entrainment as the key component of rhythmic behavior (and as a basis for later more precisely pulse-based and synchronized behaviors) is a crucial step towards our understanding of music, language and dance as well as the broader issues of human sociality, empathy and solidarity. In this paper we briefly outline the various ways in which we employ rhythmic behaviors in modern-day contexts, suggest that Rhythmic abilities are exaptations upon more directly survival oriented abilities, expand upon the evolutionary rationales for the evolution of Rhythmic behaviors in our species and finally discuss some of the methodological difficulties we are facing in trying to approach rhythm perception and production from an ethological perspective.