Essay: Sex, Death and Kefir; August 1994; Scientific American Magazine; by Margulis; 1 Page(s)
The certainty of death was absent at the origin of life. Unlike humans and other mammals, many organisms do not age and die. The process of programmed, inevitable death evolved only after our symbiotic microbial ancestors, some two billion years ago, became sexual individuals.
Any organism can die because of circumstances beyond its control: the ambience grows too hot, a predator attacks, poison gas permeates. But programmed death happens independently of environmental action: cornstalks topple at the end of the season, or a healthy elephant succumbs at the end of a century. Monthly, in menstruating women, the dead cells of the uterine lining flow through the vagina. Each autumn in the deciduous trees and shrubs of the North Temperate Zone, rows of cells at the base of the leaf stem die.