The Causes of Evolution

J.B.S. Haldane (1892-1964) was a British-born geneticist and evolutionary biologist, and one of the founders of population genetics. Perhaps immodestly, he states that "I can write of natural selection with authority because I am one of the three people who know most about its mathematical theory." He opines that "We have seen that natural selection is a reality, that the facts of variation, though different from what Darwin believed them to be, are yet such as to yield a raw material on which natural selection can work. We have also seen that variation directly induced by the environment is not in itself competent to explain the known facts of evolution. But we know very little about what is actually selected, any attempt to give a complete account of natural selection at work must be decidedly speculative." Nevertheless, "in spite of the above criticisms, natural selection is an important cause of evolution." In addition to natural selection, Haldane suggests that "It is at least quite certain that Mendelian gene differences, presumably due to mutation, have played a certain part in the origin of species," and that "There is no reason to think that bacterial mutation is a phenomenon essentially different from mutation in higher organisms, and it is not even clear that it is commoner." Haldane even addresses some theological notions, admitting that he "sometimes" reads Catholic apologists, "because their arguments are at least coherent." He writes, "Blake expressed some doubt as to whether God had made the tiger. But the tiger is in many ways an admirable animal. We have now to ask whether God made the tape-worm. And it is questionable whether an affirmative answer fits in either with what we know about the process of evolution or what many of us believe about the moral perfection of God." At the end of the book, he turns his attention to the question of mind: "If we are to have mind at all, it must probably conform to certain laws. There is no need to suppose that these laws, any more than those of biochemistry, are products of natural selection. Selection no doubt accounts for certain details, but in all probability not for the general character of mind." He concludes that "We have already seen reasons to doubt whether mind has played any important part in guiding evolution, nor should I expect it to appear in the absence of brain. My suspicion of some unknown type of being associated with evolution is my tribute to its beauty, and to that inexhaustible queerness which is the main characteristic of the universe that has impressed itself on my mind during twenty-five years of scientific work." This is an important summary work for those interested in the development of evolutionary theory.