In studying the life of cells, scientists have long focused their research on the essentially positive story of organisms' growth and self-maintenance. This story begins with cell division in embryos, progresses through the cell differentiation of early development, and arrives at the final stage of collective self-maintenance. Scientists have supplemented this story of cell growth with the discovery of different types of cell proliferation in the matured organism: that of the immune system, whereby antibody-producing cells will expand clonally to fight invaders of the organism, and that of cancer, whereby late reactivation of the otherwise healthy mechanisms of cell division and growth proceed uncontrollably, to the eventual detriment of the organism.
For many years, then, scientists immersed themselves in narrowly defined problems posed by the various phenomena of cell proliferation. However, questions remained unanswered: How are excess cells disposed of during development? How are immune cells removed when they are no
Wong F. Photoreceptor Apoptosis in Animal ModelsImplications for Retinitis Pigmentosa Research. Arch Ophthalmol. 1995;113(10):1245-1247. doi:10.1001/archopht.1995.01100100033023