“Cells constantly adjust their metabolism to available nutrients, control their progress through their cell cycle to make sure that all progeny are complete at the time of division, repair damage as it occurs, and interact appropriately with other cells. In a multicellular context, they even undergo programmed cell death when suicide is beneficial to the entire population or to the multicellular organism as a whole.”

~ James Shapiro
University of Chicago biochemist
Evolution: A View from the 21st Century