Abstract

The modern biological definition of a chimera is a single organism composed of cells with multiple distinct genotypes. Chimeras combining human and nonhuman cells are invaluable for various kinds of research, providing a platform for the study of human cell development while avoiding the ethical issues involved in conducting this research on human subjects. There is also the possibility that human/nonhuman chimeras could one day be used to produce human organs for transplant. Yet human/nonhuman chimeras raise a number of unique ethical challenges as well. Critics worry that they are ‘unnatural’, or will cause a kind of ‘moral confusion’, or pose a threat to human dignity. There are also concerns about the kinds of treatment we might owe to human/nonhuman chimeras. For example, introducing human pluripotent stem cells into a gorilla blastocyst could result in the animal developing a ‘humanlike’ brain, or developing human behaviours or characteristics. Would we need to treat such a being as we do our fellow humans? This chapter examines various arguments concerning research involving human/nonhuman chimeras, and the implications of these arguments for research policy. I conclude that research involving human/nonhuman chimeras is not intrinsically morally wrong, though it may be morally impermissible in some cases. However, I criticize the standard approach to evaluating the treatment of nonhumans in research, arguing that the moral treatment of nonhuman animals, including human/nonhuman chimeras, depends on contextual factors, rather than their moral status.