For about a decade, Hayflick’s findings languished. But then a team of researchers at the University of California at San Francisco discovered that stretches of specialized DNA at the end of each chromosome called telomeres fulfill the role of tallying device. With each cell division, telomeres shorten until eventually they reach a predetermined length (which varies markedly from one cell type to another) and the cell dies or becomes inactive. With this finding, the Hayflick limit suddenly became credible. It was hailed as the secret of aging. Arrest the shortening of telomeres and you could
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