Critical rationalism sustains that the best way of evaluating scientific theories is through the hypothetical-deductive method. Scientific hypotheses are tested deducting observational conducts from them. The task of science is to refute hypotheses, which mandates to postulate other hypotheses which can surpass the previous ones in terms of their precision and explanatory content. However, according to the Duhem-Quine thesis, the problem is that a hypothesis can never be totally refuted. In view of this, the hypothetical-deductive method appears as extremely permissive, but minimally probative. The aims of this paper are to show that: (1) the so-called ‘inference to the best explanation’ gives a more adequate answer than the hypothetical-deductive method about how to evaluate scientific theories; (2) The theory of evolution by natural selection is a clear example of what is pointed out in (1)