Imagine there was a way of preventing telomeres from shortening. In the 1990s, the same scientists who discovered telomeres also discovered an enzyme named telomerase, which, when added to cells in culture, allowed telomeres to maintain their structural integrity. As the telomeres stay long, cells can divide endlessly. The life span of such telomerase-enhanced cells can be prolonged indefinitely. This was an amazing discovery; but just because cells in vitro can be manipulated does not mean that telomerase can make humans live forever.