67 Essays on Infinite Lifespans   Michael D. West to facilitate the reproduction of their sister cells. These spe- cialized cells, which are called ‘somatic’ cells (from the Greek word ‘soma’, meaning body), lost the ability to create other organisms like themselves. They had irreversibly specialized. For the first time in history, a specialization of cell types arose. The change may have made the entire organism more fit  compared  to  its  competition,  but  the  cost  was  that  the somatic  cells  were  destined  to  die,  losing  the  potential  for their own immortality. This, Weismann argued, was the first time programmed death appeared. As Joseph Wood Krutch (1856) put it: The   amoeba   and   the   paramecium   are   potentially immortal... But for Volvox, death seems to be as inevi- table as it is in a mouse or in a man. Volvox must die, as Leeuwenhoek was to die because it had children and is no longer needed. When its time comes it drops quietly to the bottom and joins its ancestors. As Hegner, the Johns Hopkins zoologist, once wrote, “this is the first advent of inevitable natural death in the animal king- dom and all for the sake of sex. [1] The question of the actual mechanisms of aging has been one  of  the  most  challenging  questions  mankind  has  ever faced. Weismann himself, recognizing the significance of this question, carefully considered the possible mechanisms of the body’s aging. In 1881, he delivered a lecture to his fellow sci- entists at the Association of German Naturalists called ‘Über die Dauer des Lebens’, or ‘On the Duration of Life’. It was the  first  effort  to  uncover  the  mechanisms  of  aging  of  the multicellular animal utilizing the sciences of cell biology and evolution. [2] Let us now consider how it happened that the multicellular animals and plants, which arose from unicellular forms of life, came to lose this power of living forever. The answer to this