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The groundbreaking
involved injecting human
into the embryos of macaque monkeys. Scientists studied the
of the embryos for 19 days. Many people are worried about this and believe it is the
of horror movies. Professor Greely understood that there are
concerns around the creation of chimera. He said: "Every time a person gets an
transplant, the result is an intra-species chimera - an
made up of cells from two members of the same
....When a human gets a pig heart
, she becomes an
-species chimera."
