Naturalists did not use the term “symbiosis” until the nineteenth century. Nevertheless, Renaissance scholars from many disciplines were fascinated by examples of mutual cooperation between different organisms. This paper traces some of the ways that sixteenth-century French humanists thought about the mutualisms between the pilot fish and the whale, and the plover bird and the crocodile. In poetic and zoological texts alike, mutualism is simultaneously legible as an ethical social model for the human world, yet also tantalizingly opaque, suspended between sameness and difference. Taken in conjunction with some recent theoretical turns in Animal Studies, these readings show that many of the ideas central to posthumanism and queer ecology are contained within early modern humanistic discourse. The idea that Renaissance humanism was responsible for the inauguration of a violently oppositional human-animal divide is not borne out by situated readings of actual Renaissance humanist texts that instead reveal animals to be a central site of ethical inquiry.