Our understanding of evolution dates from the publication in 1859 of Charles Darwin’s great book The Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life. Before that time, explanation of all the details of animal design in terms of a divine Creator was widely accepted, though perhaps the extraordinary variety of life (e.g. what has been termed ‘the Almighty’s inordinate fondness for beetles’) was harder
to explain. From very early times a few writers had postulated evolutionary theories, suggesting that different species might not all have been separately created, and further that complicated forms of life could have arisen from simple antecedents by descent with modification. This however was mere speculation in the absence of support from a large array of ordered facts. What Darwin gave us was a mass of careful observations, many gathered while he was Naturalist on the voyage of HMS Beagle, from which he formulated a theoretical framework showing that evolution could have occurred by what he called ‘Natural Selection’. That the time was ripe for such a theory is shown by the simultaneous conclusions of Alfred Russel Wallace from his work in Indonesia. The cooperation of Darwin and Wallace without any competition for priority is an encouraging example of decency transcending competition.
Darwin’s argument was as follows:
1. Living things tend to multiply. There are more offspring than parents and, if unchecked, their numbers would increase in geometrical ratio.
2. The progeny cannot all survive, because resources (food, space, etc.) are insufficient.
Therefore there will be competition for survival, a ‘struggle for existence’ between individuals of the same species.
3. Living things vary; the progeny are not all identical and some will be better equipped for survival than others.
Therefore ‘favorable variations would tend to be preserved and unfavorable ones to be destroyed. The result of this would be the formation of new species’ (The Autobiography of Charles Darwin, ed. Norah Barlow, Collins 1958, p. 120).
To describe this process of natural selection Herbert Spencer used the phrase ‘survival of the fittest’. The phrase needs to be qualified if misunderstanding is to be avoided: firstly, it is not mere survival but differential reproduction that is required and, secondly, ‘fittest’ does not refer to general health and strength but to some precise advantage in particular circumstances in a particular environment. Adaptation consists in the perpetuation of such an advantage down the generations.
Here at once was Darwin’s greatest difficulty. For natural selection to work, advantageous changes had to be inherited. In Darwin’s time heredity was assumed to involve the blending of the features of the two parents, and Darwin was much worried by the criticism (from an engineer, Fleeming Jenkin) that any system of blending inheritance would remove the advantage in a few generations. Hie solution was at hand, but never known to Darwin. Gregor Mendel had already shown that heredity was particulate, but his work was not publicized until 1900.