When I think of evolution, I tend to think in terms of a series of what I call happy accidents. A creature through a series of genetic mutations is born with an attribute which fits well with its habitat thus providing it with an advantage over others of its kind. This advantage in turn makes the creature hardier than its compatriots leading to increased chances for survival and, perhaps, better selection of mates. This uniquely equipped animal then breeds and its new trait is passed on to some of its progeny who in turn breed, pass it on, and so forth until those with this new trait outnumber and ultimately outlast those who lack the evolutionary advantage provided through a happy genetic accident. For good or bad, I think there are also unhappy accidents which occur in much the same manner as the happy ones with an equal and opposite effect thus eliminating these unfortunate benefactors from the genetic pool through the process of natural selection.
Does the Darwinian theory of natural selection show that there is no such thing as purpose in nature, or does it show that there are purposes and they are perfectly natural causal processes (Rosenberg, 2005)? When considering this question posed by Rosenberg (2005), I tend to agree with the latter contention, believing that, in the course of things, changes occur which make creatures better suited for their environments and these traits are passed on to future generations leading to their eventual dominance and the extinction of traits or even species that do not have the fortune of experiencing such happy accidents. It is not, in my estimation, a conscious process, but one driven by purpose with traits possessed of greater utility persisting for longer periods in the natural world.
Rosenberg, A. (2005). Philosophy of science: A contemporary introduction (Second ed.). New York, New York, USA: Routledge.