We get the idea of final causes from the goal seeking nature of our own activities, as hunting is for the sake of eating, and eating is for the sake of health. But the nature of a final cause, as was said earlier, is to be the formal aspect of an efficient cause: why or how it causes. Every case of an efficient cause will have such a final cause, since otherwise the efficient cause itself would be unintelligible. However, final causes will not have entirely the same character in every case.
Thus for example the final cause of the form of the human hand is surely to grasp and manipulate objects. Darwin’s theory of evolution by natural selection implies that this form developed because people with more usefully shaped hands were more likely to survive and to have offspring than people with less usefully shaped hands. This account is sometimes used to suggest that we can say that the hand therefore has no final cause. But in reality this does not follow, for even if this happened, it happened not randomly, but with exactly the pattern of promoting hands that could grasp and manipulate objects. Thus this is the correct way to understand the process that actually happened; this is the “form” that the process took.
It was shown earlier that it is necessary that a world measured by place and time should have mathematical laws of nature. This very demonstration gives us a final cause of the fact that such laws exist: namely, in order to have a world at all. It is more difficult to explain why some concrete law has the exact form that it has. But even the exact form of the law will have a final cause, unless the law itself is a first cause, which is very unlikely, since a mathematical law is something abstract.