Here is what we know. We know that much can be learned from research on embryonic stem cells. In particular, such research may give us further insight into the processes of cell division and cell differentiation. This would almost certainly shed new light on those medical conditions, like cancer and birth defects, that seem to be merely a matter of these processes gone awry. We also know that research on embryonic stem cells requires the destruction of human embryos at the 150-cell stage. There is not the slightest reason to believe, however, that such embryos have the capacity to sense pain,
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