There is another way to interpret probabilities, however, and it is much more congenial to both quantum mechanics and evolutionary theory. We may call this the metaphysical interpretation, because it posits that probabilities reflect, not limitations in our own knowledge of the physical universe, but the stochastic properties of a non-deterministic universe. That is, on the metaphysical interpretation of probabilities, we say that there is a certain chance that something will happen not because we do not know for sure what all of the variable are that will lead to one outcome rather than another, but because it is genuinely undetermined, at the time of our prediction, which outcome is going to take place.
Although he does not say much about this in his article, Professor Barr notes that this view of probability is congenial not only for quantum theory, but also for those who endorse the idea that the human will is free. As I mentioned in one of my earlier posts in this series, if the universe is a purely deterministic place, where materialism is the only correct metaphysics, then our wills cannot be free. So if you happen to believe that your will is free, it seems that you have to abandon either materialism or determinism. Some will want to abandon both, of course: the Christian must, in my view. But even if you are wedded to your materialism it might be time to dump that dinosaur, determinism.
For those who don't find a way to work philosophical terminology into their daily routine often enough ("Oh but mommy, don't be angry, the crayon is only accidental to the wall's nature."): Determinism is the belief that with sufficient knowledge of a situation, you can invariably predict the outcome. When applied to human beings, determinism states that we are entirely the products of our genetic makeup, past experiences and current stimuli, while free will is essentially an illusion.
Determinism (in its less explicit, more popular forms) is perhaps the most pervasive remaining relic of the clockwork universe model which gained such during the two centuries after Newton.