摘要：

An advanced level chapter. There are several types of programmed cell death (e.g., apoptosis, autophagy), all important in development, and common assays may miss some types. Cell death can be used to eliminate temporary ('scaffold') structure during development (e.g., the interdigital limb bud), to eliminate one of two alternative structures (e.g., progenitors of reproductive organs of the other sex) or be used as part of a feedback system that ensures that different cell types are present in the right proportions and in the right places. The feedback system overproduces cells and then has them compete for limited survival factors, which will be available only for the cells that are needed. Survival may also depend on contact with the correct matrix, and death of 'lost' cells (anoikis) is an additional means of error correction. Elective death of somatic cells is perfectly compatible with the principles of evolution—indeed, the self-balancing it can achieve makes evolution of complex organisms over short periods of time much more likely than it would otherwise have been.

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