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and white animals after two generations, not just gray ones), whereas blending inheritance reduces variation. If inheritance were blending, the offspring of a black animal and a white animal mate, would produce gray animals indefinitely. This is obviously not the case. The fact can be seen clearly in humans: people do not become more and more alike as the generations go on. Variation is preserved.
    Darwin, who was a deeply honest man and always faced up to intellectual difficulties, did not know about particulate inheritance and was consequently very disturbed by the criticisms of a Scottish engineer, Fleeming Jenkin. Jenkin pointed out that inheritance (which, without realizing it, Darwin assumed to be blending) would not allow natural selection to work effectively. As particulate inheritance had not yet been thought of, this was a very damning criticism.
    What, then, are the basic requirements for natural selection to work? We obviously need something that can carry “information”—that is, the instructions. The most important requirement is that we should have a process for exact replication of this information. It is almost certain that, in any process, some mistakes will be made, but they should occur only rarely, especially if the entity to be replicated carries a lot of information. [In the case of DNA or RNA, the rate of making mistakes, per effective base pair, per generation must, in simple cases, be rather less than the reciprocal of the number of effective base pairs.]
    The second requirement is that replication should produce entities that can themselves be copied by the replication process or processes. Replication should not merely be like that of a printing press, when master plates make many copies of a newspaper but each newspaper cannot, by itself, produce further copies of either the press or the newspaper. [In technical terms, replication should be geometrical, not merely arithmetical.]
    The third requirement is that mistakes—mutations—should themselves be capable of being copied, so that useful variation can be preserved by natural selection.
    There is a final requirement that the instructions and their products should stay together [cross-feeding is to be avoided]. A useful trick is to use a bag—a cell, that is—to do this, but I will not dwell on this point.
    In addition, the information needs to do something useful, or to produce other things that will do useful jobs for it, to help it to survive and to produce fertile offspring with a good chance of survival.
    In addition to all this, the organism needs sources of raw material (since it has to produce copies of itself), the ability to get rid of waste products, and some sort of source of energy [Free Energy]. All these features are required, but the heart of the matter is obviously the process of exact replication.
    This is not the place to explain Mendelian genetics in all its technical details. However, I shall try to provide a glimpse of the astonishing results that a simple mechanism like natural selection can produce over long periods of time. A fuller and very readable account can be found in the early chapters of Richard Dawkins’s recent book, The Blind Watchmaker. One may wonder at the title of the book. Watchmaker obviously refers to the designer that Paley invoked to explain the imaginary watch found on the heath. But why “blind”? I cannot do better than quote Dawkins’s actual words:
    All appearances to the contrary, the only watchmaker in nature is the blind forces of physics, albeit deployed in a very special way. A true watchmaker has foresight: he designs his cogs and springs, and plans their interconnections, with a future purpose in his mind’s eye. Natural selection, the blind, unconscious, automatic process which Darwin discovered, and which we now know is the explanation for the existence and apparently purposeful form of all life, has no purpose in mind. It has no mind and no mind’s eye. It does not plan for