Now, the fourth one is the most ominous, and that is that their numbers decline precipitously, precipitously, tenfold, fiftyfold, as you age. And so what had happened, really, is that we found ourselves in a perceptual shift. We had gone hunting for pills but we ended up finding theories. And in some ways we had hooked ourselves back onto this idea: cells, organisms, environments, because we were now thinking about bone stem cells, we were thinking about arthritis in terms of a cellular disease. And then the next question was, are there organs?