Strategy for creating pluripotent cells called into question.The creation of human?animal hybrid embryos ? proposed as a way to generate embryonic stem cells without relying on scarce human eggs ? has met with legislative hurdles and public outcry. But a paper published this week suggests that the approach has another, more fundamental problem: it may simply not work. Robert Lanza of Advanced Cell Technology, a stem-cell company based in Los Angeles, California, and his colleagues show that in their labs, early-stage human?cow, human?mouse and human?rabbit hybrid embryos fail to grow beyond 16 cells (Y. Chung et al. Cloning Stem Cells...