In Greek mythology, the Chimera is a monster that is part lion, part goat and part snake. Far from reality, sure, but the idea of mixing and matching creatures is real — and has ethicists concerned.

That’s because last week, the National Institutes of Health proposed a new policy to allow funding for scientists who are creating chimeras — the non-mythological kind. In genetics, chimeras are organisms formed when human stem cells are combined with tissues of other animals, with the potential for creating human-animal hybrids.

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