Thursday, January 5, 2012

Evolution and the PSR

1. Fundamental entities evolve into more complex entities. (Premise)

2. If the PSR is false, evolution is most likely inexplicable. (Premise)

3. Evolution is explicable. (Premise)

4. Therefore, the truth of evolution implies that the PSR is most likely true. (From 1 - 3)

Since a denial of evolution leads to a conclusion incompatible with naturalism, the naturalist will almost certainly accept (1). In fact, it's hard to think of any contemporary naturalists who would reject the first premise. (3) is true on any realistic account of Darwinian natural selection. This leaves us with premise (2).

Take an inductive form of the PSR: if X exists, then X most likely has an explanation of its existence. If most things do not have explanations, then evolution prima facie has an explicability likelihood of <.5. However, evolution is explicable according to (3). This entails that the PSR is most likely true prima facie.


  1. For the record, I like this argument and hope to see more like it. Using evolution in this way seems promising.

    That said, what if someone denies 2 - say, taking the general tack that "the PSR is false, but maybe only for the beginning of/existence of the universe". I can think of some replies I believe I read in the past, but I'm curious of what yours is.

  2. As far as the kalam argument goes, the most obvious response might be that the skeptic is committing special pleading. Why should the beginning of the universe be an exception to the PSR or, more fundamentally, the ex nihilo principle? Exceptions to general principles require arguments, so I would press the atheist to provide some compelling argument.

  3. You have one flaw in your argument. Evolution does not necessarily mean change from simple to complex. It can even be complex to simple, evolution just means change in species over time.

  4. Evolution does not necessarily mean change from fundamental to complex. It can be the other way around, it just means change in species over time.

  5. Hi Jake,

    The transition from simple to complex isn't really a key feature of the argument. The point is that evolution (whether simple to complex or the other way around) is generally held by its proponents to be explicable.