Christians oftentimes criticize proponents of evolution by natural selection by mistakenly confusing it with Social Darwinism. Evolution by natural selection simply teaches that traits which are adapatively advantageous tend to be passed on to subsequent generations. It does not teach anything like a normative philosophy according to which one ought to advocate such an imperative based on this indicative. That is, just because someone believes that evolution tends to proceed by way of natural selection does not mean that one ought to preserve only those whose genes are most adaptively advantageous and euthanize the rest. Indeed, natural selection does not even teach that those traits which are passed on because of their adaptive superiority necessary consist in being able to best other species in combat.
Some traits are simply better, it is argued, at surviving a specific environment, and other traits are not, and those species with traits that are not advantageous tend to die out, with those that are advantageous tending to perpetuate themselves. If we are to critique the positions of others, it is important to do so in a way that properly represents their positions. The evolutionary Darwinist may at the same time reject Social Darwinism. On the other hand, an evolutionist is likely to reject the existence of God, it is doubtful, of course, that they will be able to coherently defend the existence of an objective morality in light of their worldview. But it is nonetheless very important to understand this distinction in order to intelligently dialogue with those with whom we disagree.