24 Biological Immortality the cause of aging, their stabilization stops aging. These are just words, but explicit mathematical theory shows that the arithmetic  of  natural  selection  can  produce  an  immortal period late in life. [13–15] Evolutionary theory can explain immortality in organisms like flies and ourselves. It also explains why some organisms are always immortal. Evolutionary theory predicts that organ- isms that reproduce by splitting their bodies into two similar parts will not age because there is no weakening of selection. After the single reproductive act, two juveniles are recovered, with no adult to undergo aging. Natural selection stays in its first phase, at all ages. These species always have biological immortality. THE MANIPULATION OF AGING AND IMMORTALITY Evolutionary biologists have been deliberately postponing aging since the 1970’s. This has been accomplished by delay- ing the period of weak natural selection over many generations by delaying reproduction. Delayed reproduction prolongs the phase when natural selection is strong. Evolution then does all the work once the pattern of natural selection has been changed and aging is readily postponed. [1, pg.39–] But there is a completely different approach to the manip- ulation of life span. What if the mortality plateau could be brought forward to earlier ages, at earlier levels of physiologi- cal robustness? Individuals that have been medically treated in this manner would no longer age. The rate at which they would die would depend on the age at which the transition to  immortality  occurs.  If  the  transition  occurs  at  an  early age, this rate might be low. That is, immortality would be fairly  healthy.  This  idea  was  published  some  time  ago,  in the  1970  science  fiction  novel  One  Million  Tomorrows  by