In Alex Rosenberg’s book Philosophy of Science: A Contemporary Introduction, Rosenberg takes a look at issues surrounding the philosophy of science. He seems to do a good job in identifying the crucial questions and classic issues raised in this area. However, occasionally, he will drop things in that seem to be out of place. One of those things is his interpretation of Darwin’s theory of evolution (with natural selection). Rosenberg claims, “Darwin’s theory is controverted by those who rightly fear its inimical implications for theism” (106). What could Rosenberg mean here? He tells us on the next page: “Darwin had succeeded in making purposes safe for physical science, showing how purposes are just complex combinations of causal sequences." (107, emphasis mine) In fact, Rosenberg seems to overstate the case for evolution and what it shows, claiming Darwin even showed “how a purely causal process—blind variation . . . can produce adaptations . . . .The appearance of design and purpose was mere illusion” (107). He triumphantly proclaims, “We must conclude . . . that there is no deity whose plan gives rise to the adaptation and complexity of biological systems” (107).
But how could Rosenberg make such claims as these? How did Darwin “show” any of this? He doesn’t say. It’s no part of the theory of evolution (proper) that it is unguided and purposeless. In order to say Darwin showed that there is no purpose, Rosenberg (or Darwin) must show not that unguided natural selection is possible, but it is the actual way things went. I can see the howls now: “Don’t you know that natural selection has been proven!?” No, I don’t know that. But suppose I do. What follows? It doesn’t follow that there is no purpose. No, the objector (or Rosenberg, or Darwin) needs the further thesis that natural selection is not only true, but unguided. That’s essentially the thesis of naturalism, and that cannot be argued for on the basis of natural selection alone.
So perhaps Rosenberg has good arguments for naturalism. If so, he doesn’t give any (it would be question-begging, in this instance, merely to insist that natural selection includes naturalism without argument). Suppose, however, as Rosenberg allows, that natural selection makes God and purposes unnecessary in explanations regarding life, and that therefore the idea of purpose is illusory (107). This is a slightly more modest claim, because it doesn’t entail naturalism, and it’s not merely claiming that unguided natural selection is actual, but merely possible.
There are a couple of responses. First, again, it is only unguided natural selection that would count against God, and so to insist it is possible doesn’t get one the conclusion that there is no God, or that God is actually unnecessary to explain it. This can be seen by granting that unguided natural selection is possible, but say very unlikely, and that, on balance, guided natural selection is more plausible. So mere possibility will not do it. They need some further reason to grant that it was actually unguided. Second, it’s not at all clear that unguided natural selection is possible. Mind arising from non-mind, and intentionality (or aboutness) from non-intentionality seem to be metaphysically impossible claims (or at least wildly implausible). Why should we think these things are possible?
The point is not to argue that, in fact, Rosenberg is incorrect and there is purpose and a God who endowed the universe with such (though obviously I think that is correct). It is to argue that Rosenberg is overstating his case. It takes a lot more than what he has given to show that God does not exist, or is unnecessary. If these metaphysical issues (or others) hold, then it’s not so much as possible that natural selection be anything other than guided.
 It should be noted, in fairness, that Rosenberg says there might be room for a deistic first cause, but that there would be no purpose that the deity had in bringing the universe into existence.