Two explanations of evolutionary progress

Natural selection explains how living forms are fitted to their conditions of life. Darwin argued that selection also explains what he called "the gradual advancement of the organisation," i.e. evolutionary progress. Present-day selectionists disagree. In their view, it is happenstance that sustains conditions favorable to progress, and therefore happenstance, not selection, that explains progress. I argue that the disagreement here turns not on whether there exists a selection-based condition bias - a belief now attributed to Darwin - but on whether there needs to be such a bias for selection to count as explaining progress. In Darwin's own view, selection explained progress so far as more complex organisms have the selective advantage when selection operates unimpeded. I show that these two explanations of evolutionary progress, selection and happenstance, answer for their objectivity to different standards, and for their truth or falsehood to different features of the world.