Free Darwin's Dangerous Idea by Daniel C. Dennett

difficulties with their view could be overcome, and, time and time again, they have succeeded in meeting the 4. As is often pointed out, Darwin didn't insist that natural selection explained everything: challenge. In the process, Darwin's fundamental idea of natural selection has it was the "main but not exclusive means of modification" (Origin, p. 6).
    been articulated, expanded, clarified, quantified, and deepened in many 5. It is sometimes suggested that Darwin's theory is systematically irrefutable ( and hence ways, becoming stronger every time it overcame a challenge. With every scientifically vacuous), but Darwin was forthright about what sort of finding it would take to refute his theory. "Though nature grants vast periods of time for the work of natural success, the scientists' conviction grows that they must be on the right track.
    selection, she does not grant an indefinite period" (Origin, p. 102), so, if the geological It is reasonable to believe that an idea that was ultimately false would surely evidence mounted to show that not enough time had elapsed, his whole theory would be have succumbed by now to such an unremitting campaign of attacks. That is refuted. This still left a temporary loophole, for the theory wasn't formulatable in suffi-not a conclusive proof, of course, just a mighty persuasive consideration.
    ciently rigorous detail to say just how many millions of years was the minimal amount required, but it was a temporary loophole that made sense, since at least some proposals One of the goals of this book is to explain why the idea of natural selection about its size could be evaluated independently. (Kitcher [1985a, pp. 162-65], has a appears to be a clear winner, even while there are unresolved controversies good discussion of the further subtleties of argument that kept Darwinian theory from about how it can handle some phenomena.
    being directly confirmed or disconfirmed.) Another famous instance: "If it could be demonstrated diat any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down" ( Origin, p. 189 ). Many have risen to this challenge, but, as we shall see in chapter 11, there are good reasons why they have not succeeded in their attempted demonstrations.

    48 AN IDEA IS BORN
    Natural Selection as an Algorithmic Process 49

    4. NATURAL SELECTION AS AN ALGORITHMIC PROCESS
    consists of two sorts of demonstrations-, the logical demonstration that a certain sort of process would necessarily have a certain sort of outcome, and What limit can be put to this power, acting during long ages and rigidly the empirical demonstration that the requisite conditions for that sort of scrutinising the whole constitution, structure, and habits of each crea-process had in fact been met in nature. He bolsters up his logical dem-ture, — favouring the good and rejecting the bad? I can see no limit to onstration with thought experiments—"imaginary instances" {Origin, p.
    this power, in slowly and beautifully adapting each form to the most 95)—that show how the meeting of these conditions might actually account complex relations of life.
    for the effects he claimed to be explaining, but his whole argument extends to book length because he presents a wealth of hard-won empirical detail to
    —CHARLES DARWIN, Origin, p. 469
    convince the reader that these conditions have been met over and over again.
    Stephen Jay Gould (1985) gives us a fine glimpse of the importance of this The second point to notice in Darwin's summary is that he presents his feature of Darwin's argument in an anecdote about Patrick Matthew, a principle as deducible by a formal argument— if the conditions are met, a Scottish naturalist who as a matter of curious historical fact had scooped certain outcome is assured.6 Here is the summary again, with some key Darwin's account of natural selection by many years—in an appendix to his terms in