Intrinsic finality is the idea that there is a natural good for all beings, and that all beings have a natural tendency to pursue their own good. It is an underlying principle of both teleology and moral objectivism. The concept of intrinsic finality was summarized by Thomas Aquinas as follows: The idea of intrinsic finality presumes an objective reality that obeys a natural order or natural law in the universe. Things are "meant" to be and behave a certain way, and naturally tend to act that way. For instance, animals have natural instincts for self-preservation, seeking food, and reproduction. They do so because it is their nature to do so. Theologians go further, to argue that they do so because they were created to do so. The existence of such a finality is often challenged, particularly by philosophers ascribing to philosophical naturalism. They argue that it is unreasonable to say that all beings naturally pursue their own benefit, when some beings clearly do not. They point to instances of imperfection, disease, and death as evidence that natural beings do not naturally move toward perfection. But proponents of intrinsic finality respond that the very recognition of such imperfection requires an ideal or standard of the perfect end from which the being in question falls short owing to a variety of factors including improper education, sin, or predestination. Intrinsic finality provides the basis for the teleological argument for the existence of God and its modern counterpart, intelligent design. Proponents of teleology argue that Darwinism does not resolve a fundamental defect in philosophical naturalism; that it focuses exclusively on the immediate causes and mechanisms of events and does not attend to the reason for their synthesis. For example, if we take a clock apart, we discover in it nothing but springs, wheels, pivots, levers and so on but does our having explained the mechanism which causes the revolutions of the hands on the dial make it reasonable to say that the clock was not made to keep time? Naturalists respond that biology has been profoundly concerned with the ways function constrains structure since the time of Aristotle and that Darwin's own awareness of teleology is evident in his study in functional constraints on the evolutionary development of the beaks of Galapagos finches, of which he wrote, "Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends."
