Life itself is inherently purposeless, insofar that the only purpose in life is to perpetuate itself. From an individual perspective, this is self-evident; the same holds from a global perspective. And yet, our human situation leads one to wonder why certain facilities of life exist. For example, what is the purpose of intelligent life? Certainly, intelligence grants an advantage towards those who have it; that is not contentious. Stepping outside of a purely human perspective, and looking at the viewpoint of life as a whole, the evolution of intelligence was probably the worst thing that ever happened. But the myopic greed of intelligent beings (viz. humans) is hardly blamable, nor is it unique to our station. Rather, it is merely a strong refinement. In effect, the world is at our disposal, for us to use or destroy.
As an adaptation of life as a whole, then, what good is intelligence? The dominance of one species over others does not require intelligence, and the burden of conscience, of existential sentience, hardly seems a meet price, for I can conjure up sadness and misery, where (presumably) other species cannot. And in general, the ability to feel and to know only leads to disappointment: entropy always wins in the end. Life as a whole, however, is limited in one respect. While it can occupy all areas of the earth, it is stuck there. Only through some improbable events well outside of any control could non-intelligent life, and then only the simplest, escape the grasp of gravity.
Intelligent life, however, has the capacity to transcend this limitation in ways that are impossible for non-intelligent life. The additional benefits for survival in its own land are only a preamble to the ultimate purpose of sentience. All of civilization and society, science and art, human achievement, is merely facilitation towards the goal of expanding life outside the boundaries from which it is born.
Intelligence, then, is an evolutionary adaptation of life as a whole to propagate itself outward, outside the realm of the earth. The survival of life, even after the earth itself falls, is the prerogative of the human race. That is not to say that our task is merely to ensure human survival. Quite the opposite, our task is to be the carrier of life itself, not necessarily our just own but earth life as a whole, to the stars.