AN ADAPTATIONIST VIEW OF APOPTOSIS

A cell's decision whether, to undergo apoptosis (cell suicide is exami ned from an adaptationist perspective, rather than a mechanistic one. External and internal inputs to the cell's protein-based information p rocessing network are used in making this decision, with the cell fact oring in its replaceability. A system in which each cell fakes primary responsibility, deciding its own fate has great adaptive value becaus e it harness each cell's self-knowledge rather than waiting for extern al cues to be recognised by other cells. Cell self-destruction can be an important selective mechanism, potentially leading to better perfor mance of tissues over time. However, reliance on cells to monitor them selves has a flaw, since cells may incur selfish mutations that impair , their apoptotic responsibility. The tight control exerted over somat ic cells serves to check selfish genes involved ill neoplasia and vira l infections. Germ cells appear to be similarly monitored, both by oth er germ cells and by supporting follicular or Sertoli cells, thus main taining the advantages offered by an apoptotic system. The adaptationi st approach views the limited replacement of neurons and cardiac myocy tes as likely to have net survival value. The linkage of these cells i nto a network with their neighbours throughout a lifetime allows for a precisely functioning team of cells expected to compensate for gradua l declines in individual cell functionality. Replacement of apoptotic cells with naive cells might decrease brain functionality and might ri sk upsetting the conduction of cardiac impulses. The evolutionary view point lends itself to new hypotheses, but only tile boldest speculator would have predicted a system in which cells are given primary respon sibility for deciding whether to kill themselves when they deem it ben eficial to the organism.