THE TRANSITION POINT. “In other words, was there a period ‘before’ programmed cell death, in which cells died only ‘from without’, as a result of chance and environmental destruction, and a period ‘after’ programmed cell death, in which regulated self-destruction, the capacity to trigger premature death ‘from within’, became one of the intrinsic properties of the cells?”
http://www.nature.com/cdd/journal/v9/n4/full/4400950a.html