A friend of mine says he has formulated a theory about life which suggests that a decent percentage of cells in a multi-cellular organism doesn't contribute to the organism as a whole and merely exists eating away its resources. Generally speaking, not all cells of type x supposed to do some function y for the body do it, he says. For example not all well-developed cells of the islets-of-langerhans synthesise insulin, not all liver cells secrete bile etc etc. I tried googling about this but no website covered this area. Maybe i need to refine the search terms. Can any of you knowledgeable in this field say whether he is right because this is stunning for me!