Ward argues that the theory of evolution by natural selection on its own does not allow us to conclude that the existence of sentient life-forms is more probable than not. Adding the hypothesis of a God who sets up the process of mutation with the intention of bringing sentient life into being does, however, make the existence of such life-forms probable. And, as it is the mark of a good theory that it makes the facts to be explained probable, the God-hypothesis, argues Ward, is superior to the hypothesis of natural selection considered alone.