Before Darwin nonbelievers had more difficulty explaining how we came to be here. Darwin’s theory of natural selection filled out an explanation. By and large this has been viewed as helpful to the atheist’s position. But when you start attaching explanations you start making affirmative claims. And once you start making claims you open yourself up to the possibility of logical inconsistency.
For example, Christians explain certain qualities God has: Omnipotent, Omniscient, Creator of everything, Good through and through etc. Doing this opened them up to the argument concerning the problem of evil. I think there are valid ways around the problem of evil but there can be no question that this problem was created because Christians offered explanations of what God is. Having the problem of evil to contend with is logical baggage from the claims that God has these attributes. If Christians just continued to shrug when asked if God was all knowing, all powerful, etc then they wouldn’t have this problem.
So now the atheist no longer just shrugs when the theists ask how we came exist. They have an explanation of how humans could come about from other life without God. On the surface it seems good for them. But when we start to understand what that process is we start to see that problems can arise.
I think Descartes was anticipating problems long before Darwin. He noticed that to the extent one were to say we are the product of something less than a perfect being then we would have more reason to suspect the reliability of our beliefs:
“Some, indeed, might perhaps be found who would be disposed rather to deny the existence of a Being so powerful [God] than to believe that there is nothing certain. But let us for the present refrain from opposing this opinion, and grant that all which is here said of a Deity is fabulous: nevertheless, in whatever way it be supposed that I reach the state in which I exist, whether by fate, or chance, or by an endless series of antecedents and consequents, or by any other means, it is clear that the probability of my being so imperfect as to be the constant victim of deception, will be increased exactly in proportion as the power possessed by the cause, to which they assign my origin, is lessened.”
It is clear this concern was not baggage from natural selection since Descartes wrote this over 200 years before Origin of the Species was published. But it clearly anticipates logical problems that any unbeliever will face. What baggage natural selection actually creates with respect to the reliability of our beliefs will be the topic of several of these blogs.
End Note: I should clarify that by “natural selection” I mean “natural selection and naturalism” – ie, no God. However, there is no reason to think that Christians can’t understand that they have evolved from a system along the lines of natural selection any more than we need to deny that we came about from the interaction of sperm and egg. Some people would want to claim it is incompatible with Christianity due to randomness natural selection presupposes. But really there are all sorts of things that are random to us but not to God and Christians always understood God might be acting in the world in ways we don’t know. This would including which sperm reaches which egg. So, natural selection really raises nothing new.