Lynn Margulis’s writing about symbiosis has profoundly influenced contemporary evolutionary theory, as well as continental and analytic philosophy of science, the materialist turn, and new materialism. Nonetheless, her work, and all symbiosis or evolution, is founded on a paradox: symbiosis fictionalizes customary accounts of the origin and evolution of species, yet it is impossible to speak of symbiosis (cross-species association) unless species-boundaries have been posited in advance. Thus, a tension is legible throughout Margulis’s work between the drive to surpass the limits of species-definitions as they have been traditionally understood, and a need to maintain them in order that there can be “symbiosis” at all. Margulis criticized neo-Darwinian accounts of evolution in part because she saw symbiogenesis as debunking the theory that life was defined by individualistic competition. More recently, Myra Hird has suggested that the gift, such as it has been theorized by certain anthropologists and philosophers, could adequately figure symbiosis and the ethical relations founded on it. I turn to Derrida’s writing on the gift to suggest that, if a gift worthy of the name chances to happen, it necessarily exceeds scientific, theoretical, and philosophical knowledge.