The question of whether the sense of fairness constitutes an exclusively human trait has been answered mostly from two polar positions: the first one unambiguously affirms such exclusivity, thus denying the relevance of cognitive ethology to understand our evaluations of justice; the second one, on the contrary, postulates the existence of a (proto) sense of fairness in non-human animals, strongly related to ours, which would make cognitive ethology highly relevant to understand the mechanisms on which our evaluative practices are based. From a position of extreme caution in relation to the possibility of (eventually) offering concrete evidence in favor of innatist theses such as the one I will defend here, I will suggest that i) in line with the rupturist positions, it is possible to preserve the human exclusivity of the sense of justice, ii) in line with the continuist positions, the relevance of studies coming from cognitive ethology is guaranteed, insofar as (ex hypotesi) our evaluative practices often take as input innate psychological dispositions shared with other species. Finally, I will suggest that the concept of rationalization is central to determine in each case the possible articulation between innate dispositions and explicit justifications.