Programmed cell death
Programmed cell death (PCD) is another suggested form of microbial altruistic behavior. Although programmed cell death (also known as apoptosis or autolysis) clearly provides no direct fitness benefit, it can be evolutionary adaptive if it provides indirect benefits to individuals with high genetic relatedness (kin selection). Several altruistic possibilities have been suggested for PCD, such as providing resources that could be used by other cells for growth and survival in "Saccharomyces cerevisiae". While using kin selection to explain the evolutionary benefits of PCD is common, the reasoning contains some inherent problems. Charlesworth (1978) noted that it is extremely hard for a gene causing suicide to spread because only relatives that do NOT share the gene would ultimately benefit. Therefore, the possible solution to this problem in microbes is that selection could favor a low probability of PCD among a large population of cells, possibly depending upon individual condition, environmental conditions, or signaling.