What makes each of us, as individuals, human to one another, or, more generally, what makes an individual creature human? We have not often had to ask the question because of the species line based on reproductive capacity and incapacity, although "degrees of humanness" were explored in the various eugenic programs of the last century. Now the biotechnological possibility of fusing human and other forms of life is presenting the question in a new and serious way. If the traditional biological means of defining species are no longer reliable, what other criteria might determine what is "human" and what is "nonhuman?" The issue is not just how to conceive of an individual hybrid presented to us, but how to act toward the creature, at the most basic level. Drawing on animal law and theory as well as the history of human eugenics in law and policy, this essay surveys criteria that may one day be used to gauge relative humanness, qualitative and quantitative. It observes that ultimately the difficulty of deciding or agreeing upon what identifies us as human will make even more problematic the current treatment of creatures deemed purely "animal." In the end it suggests that what the human distinctively brings to the sentient world is general responsibility itself, and that wider contemplation of the real possibility of human-animal hybridization may lead to new ways of thinking about animals, in law and beyond.
Vining, Joseph. "Human Identity: The Question Presented by Human-Animal Hybridization." Stan. J. Animal L. & Pol'y 1, no. 1 (2008): 50-68.