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For the first time, biologists have succeeded in growing human stem cells in pig embryos, shifting from science fiction to the realm of the possible the idea of developing human organs in animals for later transplant. (Wade, 1/26)

The human-pig hybrid — dubbed a “chimera” for the mythical creature with a lion's head, a goat's body and a serpent's tail — was “highly inefficient,” the researchers cautioned. But it's the most successful human-animal chimera and a significant step toward the development of animal embryos with functioning human organs. (Kaplan, 1/26)

The ethical concerns focused on the possibility the human cells could create animals that had human brain cells or tissues, blurring the line between the species. There are also concerns the cells could form human eggs or sperm in farm animals such as cows, sheep or pigs, and then those animals could mate. (Stein, 1/26)