Chapter Variation and Struggle of The Origin of Species - Study Guide by Charles Darwin

Variation and Struggle

Darwin's innovation over previous evolutionary theorists was to provide a workable (and still largely correct) mechanism through which biological change could occur. However, in Origin he does not dive straight in, and the term "Natural Selection" is not explained until the fourth chapter. At every point Origin is meticulous in the forwarding of its argument - each chapter contains sub-headings of the subjects up for discussion and a summary of the points raised at the end. He was clearly anxious to leave no room to be misunderstood, misinterpreted or misrepresented. That he has been all of the three has been consistently the fault of his opponents rather than the text itself - the first two editions at least.

Darwin saw that the crucial raw material for natural selection - and this is as correct as it was in 1859, as it was billions of years ago - is variation: "These individual differences are highly important for us, as they afford materials for natural selection to accumulate." Darwin was attempting to produce a work of 'popular', or at least accessible science, and rather than confront his readers with the alien world organisms in the state of nature, he begins by introducing the concept of variation through that which is found in domesticated plants and animals. The mechanism through which variation is used to accentuate change in domestic animals and produce varieties - i.e. Artificial Selection - also provides a useful parallel to the workings of Natural Selection.

Mankind has been domesticating, breeding and changing the nature of organisms under his control for thousands of years - sometimes accidentally, but often deliberately. One of the key elements of the switch from nomadic hunter-gatherer societies to settled agricultural communities (the first instances, we now know, being around twelve thousand years ago) was the domestication of both plants and animals. Domestication is not simply the socialisation of individuals, but the selection of traits over generations desirable for the human owners. Darwin recognises that developmental and environmental conditions could only go so far to explaining variation under domestication. Of domestic plants he notes that by examining the development of pollen and ovule one can show that "variation is not necessarily connected, as some authors have supposed, with the act of generation." Clearly there are hereditary factors at work, though at times Darwin does slip back into Lamarckian explanations for variation, attributing use and misuse for changes over generations. For example, "The great and inherited development of the udders in cows and goats in countries where they are habitually milked, in comparison with the state of these organs in other countries, is another instance of the effect of use."

Largely though, he stresses the importance of inheritance of character in both animal and human pedigrees: "Perhaps the correct way of viewing the whole subject," he concludes, "would be to look at the inheritance of every character whatever as the rule, and non-inheritance as the anomaly." However, "The laws governing inheritance are quite unknown; no one can say why a peculiarity in different individuals of the same species, or in individuals of different species, is sometimes inherited and sometimes not so; why the child often reverts in certain characters to its grandfather or grandmother or other more remote ancestor; why a peculiarity is often transmitted from one sex to both sexes, or to one sex alone, more commonly but not exclusively to the like sex." It is notable that these examples (and others) that Darwin gives of puzzles of inheritance are among those solvable with the simple application of Mendelian Genetics (see Missing Links and Further Reading). Though Darwin did not have the answers with regard to inheritance, he was certainly asking the right questions.

So Darwin establishes that characteristics are often inherited - a far from radical claim - and he goes on to argue that different animal breeds have descended from an original wild stock, not, as some believed at the time, with each descending from an individual wild prototype. In, for example dogs, this is confirmed that however different the breeds they all seem capable of interbreeding. Indeed, writes Darwin, the naturalist tends to know "far less of the laws of inheritance than does the breeder." And from this understanding follows the breeder's selection: "The key is man's power of accumulative selection: nature gives successive variations; man adds them up in certain directions useful to him... Breeders habitually speak of an animal's organisation as something quite plastic." However, as always the raw material of variation must be there first, as man "can never act by selection, excepting on variations which are first given to him in some slight degree by nature." Artificial Selection, like Natural Selection does not induce variation, it can only work with it. Darwin notes that in artificial selection it often becomes a process of exaggeration, due to