The Moral Status of Human-Animal Chimeras in Regenerative Medicine

Abstract

Interspecies blastocyst complementation and related techniques for creating human-animal chimeras have moved from theoretical possibility to active laboratory practice, driven largely by the promise of growing humanized organs for transplantation.
This progress has outpaced the philosophical literature's ability to settle a prior question: how much human biological contribution, of what kind and in what tissue, changes an animal's moral status. This perspective surveys capacity-based, kind-based, and degree-based frameworks for moral status and applies them to three chimera types of current scientific interest -- humanized-organ pigs, neural chimeras and brain organoid transplants, and early-stage monkey-human embryos. We argue that these three cases warrant markedly different levels of ethical concern, with humanized-organ research raising primarily confinement and welfare questions while neural chimera research raises harder, still largely unresolved questions about capacity and detection. We conclude that governance structures for chimera research have not kept pace with the science, and that resolving disagreement between frameworks matters less, in practice, than building oversight bodies equipped to actually apply any of them.