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Natural Selection
Darwin entitled his famous abstract The Origin of Species by Means of Natural Selection, which is really a concise summary of his entire theory. Over the twenty years or so that he had worked on it he had written hundreds of letters to animal and plant breeders all over the country soliciting replies to questions. He drew extensively from their experience. Breeders selected those variants or varieties having characteristics of commercial value for breeding, while less promising varieties were denied opportunities to breed. Artificial selection of this type produced cows giving greater quantities of milk, horses of greater running ability, and so on. Darwin believed that, in a similar way, nature selected out those variants among the species that were best fitted for the environment. However, selection under natural conditions was known to be very conservative; that is, offspring tended to be like the parents, and anything too far from the normal would, breed back to the basic type, a fact Darwin was fully aware of from his work with the pigeons. He acknowledged all this but then argued that natural selection becomes a force for change when the environment changes. He believed that variation was going on all the time within a species, but that only those variants most closely adapted tended to survive. He said that a change in the environment would, in the course of many generations, produce gradual changes and eventually lead to a separate species. This required dynamic conditions of continuous and random variation within the species and a changing environment. One other feature of Darwin's natural selection was sexual attraction. He pointed out that in the courtship rituals of animals, the males compete for the females in tests of strength, and the strongest or the swiftest victors have the opportunity to reproduce; the losers tend to have much less opportunity and so would eventually die out. In the case of birds, the males display their plumage, and the hen bird chooses the most sexually attractive mate according to her standard of beauty. Darwin did not explain why sexual selection applied only to the males and not the females, nor why blind nature should be concerned with the preservation of beauty (Darwin 1859, 89).
Throughout the Origin, and from one edition to the next, Darwin was never entirely clear in his own mind about "end purpose". In the case of artificial selection, man intelligently controls the breeding to produce an improved end result. Under natural conditions, Darwin appealed to blind chance, which could have no innate intelligence, but there was a dilemma: the theory said that life began as a simple organism and evolved into more complex organisms, which implies an intelligent directing force, but he wanted at all costs to avoid any kind of inference to the supernatural. To circumvent the dilemma, he steadfastly avoided using the terms "lower" and "higher" forms of life[9] and spoke rather of "change", which allowed him greater freedom for argument when discussing specific cases (F. Darwin and Seward 1903, 1:114; Mayr 1972).[10] However, his most artful device was use of the word "descent", which he introduced in the first edition of the Origin and continued to use throughout his writing to his Descent of Man, published in 1873. Unlike the word "ascent", which in the context of a sequential process implies purposeful direction, the word "descent" has rather the connotation of the blind laws of nature, such as water "finding its own level". In other words, "descent" does not imply purposeful design or a Designer. Darwin did allow himself use of the word "perfection", in the sense that the organism progressed towards perfect adaption to its environment.
This, then, is classical Darwinism, which died a slow death more than half a century ago. The theory was facile, tidy, and convinced many, including Thomas Huxley, who, after reading the Origin, confessed how stupid he was not to have thought of the theory himself (L. Huxley 1900, 1:170). Lyell's geology had provided all the time thought to be necessary for evolution to take place and at the same stroke had precluded any possibility of proving the theory by laboratory experiment. There were many unanswered questions. Do animals really change in a changing environment or are they more likely to migrate or simply die out? Then again, what if the environmental change was too rapid for the proposed adaptation from random variation to keep up?
Overriding all these and other questions was the total absence of any fossil evidence. Nevertheless, the theory was superficially convincing for those who wanted an alternative to the traditional supernatural explanation. It was this version of the theory, with all its deficiencies and assumptions, that challenged theological dogma in the last half of the nineteenth century and the beginning of this century. More will be said of this confrontation in Chapters Thirteen and Fourteen, but in the meantime the shifting grounds for the theory need to be traced into this present decade.
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