Whitehead makes the startling observation that "life is comparatively deficient in survival value." If humans can only exist for about a hundred years, and rocks for eight hundred million, then one is forced to ask why complex organisms ever evolved in the first place; as Whitehead humorously notes, "they certainly did not appear because they were better at that game than the rocks around them." He then observes that the mark of higher forms of life is that they are actively engaged in modifying their environment, an activity which he theorizes is directed toward the three-fold goal of living, living well, and living better. In other words, Whitehead sees life as directed toward the purpose of increasing its own satisfaction. Without such a goal, he sees the rise of life as totally unintelligible.