To describe the evolving characteristics of a group of organisms, one must learn to think in four dimensions, three dimensions of space stretched across a very long dimension of time. The only way I can even begin to imagine what evolutionary thinking might be like is to try to look at my friend as an integrated historical sequence rather than as the individual who confronts me here and now. Not an easy task. In addition, the uniqueness of such historical sequences impedes usual scientific thinking, which does best when dealing with recurring events. Far from the reductionist ideal, evolutionary biology requires a holistic approach to science.
Most people find holistic thinking difftcult.
In general, the move away from reductionism has about as much appeal as the uncertainty principle of quantum mechanics had for Albert Einstein. It is not scientists alone, however, who prefer reductionistic descriptions. It took New Testament scholars 1,800 years to begin a hermeneutic approach to biblical interpretation. In summary, it does not surprise me that Professor van Inwagen has noticed the variable meanings and implications of Darwinism. Like much of science, understanding Darwinism requires us to use our imagination in novel ways that go beyond everyday experience, to use conceptual and mathematic models that can only be approximated by everyday language.