The Theory of Natural Selection

On the Origin of Species By Means of Natural Selection is the grand theory of the age of grand theories. As Darwin himself expressed it, it was a theory about all organisms throughout all time "by which all living and extinct beings are united by complex, radiating and circuitous lines of affinities into one grand system". Darwin took the analogy of a tree to symbolise his vision:

"The green and budding twigs may represent existing species. At each period of growth, all the growing twigs have tried to branch out and on all sides, and to overtop and kill the surrounding twigs and branches, in the same manner as species and groups of species have tried to overmaster other species in the great battle for life."

Establishing the argument for natural selection began by pointing to artificial selection, the kind engaged in by the pigeon fancier and stockbreeder. Working on the variation naturally and randomly occurring within species, better breeds are produced. Natural selection also works on these variations in the wild, in context of the struggle for existence where more organisms are born than can survive and reproduce. Those better adapted, fitter, are more likely to survive and leave more offspring.

Where Malthus used the metaphor of struggle for existence in relation to collective activity, that of tribes, Darwin saw the struggle taking place at the level of the individual: "individuals having any advantage, however slight over others, would have the best chance of surviving and of procreating On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed". A secondary mechanism, sexual selection, is added to the struggle for food and survival. In sexual selection the struggle is for mates and reproductive success. Natural selection means increase in frequency of those best adapted, their characteristics spread through a whole population, until the average character of a species changes.

All life is genealogically connected by the process of "descent with modification." Small changes that are continually underway, it is assumed, will eventually add up to give the major developments, the appearance of new forms of life. To accommodate his theory Darwin needed huge amounts of geological time to permit natural selection to operate and to house the fossil record of this evolutionary process. His discussion of the geological record, despite the acknowledged gaps, points out that more general and linking forms are found lower, hence earlier in the fossil record with more specialised forms higher and hence later, life never moves back on itself. Natural selection occurs within geographic distribution across specific environments, the fitter survivors are those best adapted to take advantage of their environment.

"From the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is a grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved."

A grand unifying theory obviously had to include mankind. "The subject of man and his place in nature was so woven into Darwin's thought that it forms an indispensable part of the nature of his beliefs." The first passage in the Darwin notebooks that clearly enunciates the idea of natural selection and applies it to man was written on November 27 of 1838. In another of his notebooks Darwin noted "I will never allow that because there is a chasm between man ... and animals that man has a different origin". What Darwin would not allow he took a very long time to get around to saying. "Light will be thrown on the origin of man and his history" Darwin had written in Origin. Both the intensely Christian Charles Lyell, Antiquity of Man 1863, and Huxley, Man's Place in Nature, 1863, published before Darwin. The Descent of Man, could have been no surprise when it was finally published.

Darwin left plenty of scope for those who would interpret natural selection as theistic evolutionism, creationism. "As natural selection works solely by and for the good of each being, all corporeal and mental endowments will tend to progress towards perfection". Intellectual adjustment reasoning along this line had been underway since the Reformation. Experts argue vociferously whether Darwin himself remained a believer or not, maybe he did maybe he did not, most likely he devolved into a vestigial agnosticism. Darwin explicitly defended the idea that evolution by natural selection did not have an intentional design, which would invoke the old idea of creation by design his entire theory sought to replace. But he very clearly inserted and permitted the progressive, upward escalator of progress idea that had long been the understanding of God's providential purpose in the creation of natural law. His imagery of nature red in tooth and claw could nevertheless be understood as all being for the best in the best of all possible worlds.