“Every time a person gets an organ transplant, the result is an intra-species chimera: an organism made up of cells from two members of the same species,”

“Another example is the way that some pregnant women end up permanently carrying cells from their fetus. When a human gets a pig heart valve, she becomes an inter-species chimera. When a mouse gets human cells, for example to test to see how committed they are to a development path (whether or not they are “pluripotent”), that’s a chimera.”

“That means that the human cells, and the monkey cells, are so early in their development that the human cells might end up in any body tissue,”

“They tried the monkeys to see if the human cells would do better in this closer species (answer: yes) and whether that could help them learn how to make human cells thrive in pig or sheep embryos (answer: way too soon to tell),”