In this article, the question of human nature is confronted from what may be called an existential-humanistic ecopsychological perspective. From this perspective, human nature is interpreted to be a synthetic, bipolar human-animal boundary form. The global character of this living form is noted to be a dynamic, oscillating hermeneutical-dialectical interplay between humanitas and animalitas. This appropriation of the human-animal boundary idea provides a wide-open, welcoming space for diverse conceptualizations of human life. At the same time, it maintains that human beings and nonhuman animals are indubitably embedded in a natural world within which we are active coparticipants in the development of experiential perspectives on our own bodies, those of others, and the natural environment at large.