Classic Paley-style design arguments go like this: There is some complex biological feature C which is such that
1. God would have good reason to produce C, and
2. C is extremely unlikely to occur through a random combination of elements.
It is concluded that probably God produced C, and hence probably God exists. The standard story is that Darwin undercut Paley-style arguments by providing a plausible explanation that does not involve God.
I shall suggest that the story is not so simple, and that, in fact, a very powerful Paley-style design argument may continue to go through.
Pruss later mentions that he thinks there’s a possible flaw in the argument, but not one due to Darwin. More on that below.
While my point that Darwin hasn’t undercut design arguments stands, there is a serious flaw in the argument I gave, which has not been noticed in the above discussion.
Here’s the flaw. Assume intelligent life supervenes on arrangement of matter. As a dualist, I think this assumption is false, but my design argument shouldn’t depend on dualism (Paley’s doesn’t, after all). In my discussion of option (4) in the original post, I noted that in the classical setting ergodicity by itself yields the claim that almost surely (i.e., with probability one) intelligent life will occur at some time or other. That’s why my explanandum is (5) rather than (4): Why is there intelligent life at t1? But this opens my argument to a very serious objection. I have granted (assuming materialism) that we’re going to get intelligent life at some time or other. Now, if t1 were a randomly chosen time, and we observed that there is intelligent life at t1, then we could use the fact that there is intelligent life at t1 as evidence. But the method by which I came up with t1 was biased–I, who am an intelligent being, chose a time at which I already knew there are intelligent beings, namely the present. So on its face we have here a case of selection bias, akin to that which earlier this fall I was exposing in Rowe’s argument from evil.
Now, I actually think that the argument can perhaps be saved, but only at the expense of controversial epistemology. One method for saving the argument might require thirding in Sleeping Beauty. But all of this is tricky.
Philosopher Joshua Rasmussen chimes in that he thinks the flaw Pruss has identified isn’t as serious as he thinks it is, and in my view the entire discussion ends up being very interesting, though inconclusive.
Naturally, I find the very move Pruss makes interesting – accepting Darwinism and materialism for the sake of argument, and invoking Paley anyway? That’s the sort of thing that should turn everyone’s head.
I offer this exchange up with minimal commentary from myself, since what I find interesting here aren’t any extrapolations we can necessarily draw from Pruss’ argument, but the argument and approach itself. Give it a read and ponder.
Note that Pruss also offered up a similar argument based on the initial low entropy of our universe, for those who enjoy philosophical design arguments.