Where the Conflict Really Lies: Science, Religion, and Naturalism Read Online Free PDF

organisms. Of course if in fact the eye
did
develop in this way, there would have to be such a path connecting life forms that had existentinstantiations. Fourth, the points on the path will have to be temporally indexed, with the temporal distance between a pair of points on the path being sufficient for the relevant mutation to spread through the population in question. That means that the time elapsed from that initial population of unicellular organisms to the appearance of the eye imposes a constraint on the number of points the path in question can contain and the temporal distance between them; the number of points the path contains and the temporal distance between them can be large but is not unlimited.
    Finally, and crucially, what is the force of “could plausibly” in “each point along the path is such that it
could plausibly
have come from a preceding point on the path by way of a heritable random genetic mutation?” We’re not talking broadly logical possibility, of course; we’re not asking whether there is a possible world in which this development takes place. That would be much too weak; to use a Dawkinsian example, there are possible worlds in which the bronze statues in the park (constituted just as they presently are) wave goodbye when you leave. We are instead talking about something like
biological
possibility, and, as Dawkins thinks of biological possibility, it is to be explained in terms of
probability
. A given point on a path could plausibly have come from a preceding point by way of genetic mutation just if it is not too improbable that it do so. It might be possible in the broadly logical sense that a sufficiently complex single mutation take us all the way from a paradigm reptile to a paradigm mammal—possible, but far too unlikely. So the mutations must be reasonably probable, not too improbable, with respect to the previous point. Not too improbable, of course, apart from any special divine aid or special divine action. The mutation in question would have to occur and be caused in the usual way—by way of cosmic radiation, or x-ray, or chemical agent or whatever—but not by way of special divine action. How much improbability is too much? Here one can answer only in the vaguest terms. Dawkins suggests, sensibly enough, thatthe improbability would have to be much less than that of that statue waving at us as we leave the park.
    How does Dawkins answer (BQ), or rather, his tripartite version of it? (3), you recall, was the question “Is there a continuous series of Xs connecting the modern human eye to a state with no eye at all?” His reply: “It seems to me clear that the answer has to be yes, provided only that we allow ourselves a
sufficiently large
series of Xs.” 27 No doubt he’s right about (3); surely there is such a relevant series. We can see this as follows: consider a particular human eye—one of Dawkins’s, for example; assign a number to each cell contained in that eye (as with certain kinds of build-it-yourself toy kits); let the first member of the series be a creature that has cell number 1, the second be one that contains cells number 2 and number 1; the third contain cell number 3 plus cells number 1 and 2, and so on. This won’t quite work; for this eye to function, there will also have to be an appropriate brain or part of a brain to which it is connected by an optic nerve. But you get the idea: clearly there is such a series. Of course that by itself doesn’t show much; if it’s to be relevant, the length of the series will have to be constrained by the time available, and each step in the series will have to be such that it can arise by way of genetic mutation from a previous step. Furthermore (and crucially), each mutation will have to be fitness-conferring (or at least not unduly costly in terms of fitness), so that it’s not too improbable that they be preserved by natural selection. This is where his answers to (4) and (5) come in.
    Dawkins’s