Darwin

Charles Darwin, The Theory of Evolution (1859/1871)

Charles Darwin (1809_1882) was the grandson of Erasmus Darwin, a noted Enlightenment scholar and free_thinker(religious skeptic). Charles proved a poor student, preferring to go riding and hunting with his friends, and he dropped out of medical school. The young man was then sent to Cambridge University to study for a career in the Church. Equally unsuited for and uninterested in that field of study, Darwin, who had by then shown an interest in nature and natural science, accepted an invitation in 1831 to accompany a British naval expedition to South America, where he spent several years observing and collecting the local plants, fossils, etc. Some of his most important observations took place in the Galapagos Islands, west of Ecuador, but he also visited many other places during the H.M.S. Beagles five_year voyage around the world.
        When Darwin returned, he did not immediately begin publishing his findings. Instead, he waited some twenty years, sharing his ideas only with a few close friends. But when he read another scientists paper sketching out the theories he had developed, he decided to move quickly, and he published The Origin of Species in 1859. That work made him famous û and controversial û almost immediately, and he later published the even more controversial Descent of Man in 1871. The following excerpts are from those two books.

The Origin of Species

From September 1854 I devoted my whole time to arranging my huge pile of notes, to observing, and to experimenting in relation to the transmutation of species. During the voyage of the Beagle I had been deeply impressed by discovering in the Pampean formation [in Argentina] great fossil animals covered with armor like that on the existing armadillos; secondly, by the manner in which closely allied animals replace one another in proceeding southwards over the Continent; and thirdly, by the South American character of most of the productions of the Galapagos archipelago, and more especially by the manner in which they differ slightly on each island of the group, none of the islands appearing to be very ancient in a geological sense.
        It was evident that such facts as these, as well as many others, could only be explained on the supposition that species gradually become modified; and the subject haunted me. But it was equally evident that neither the action of the surrounding conditions nor the will of the organisms (especially in the case of plants) could account for the innumerable cases in which organisms of every kind are beautifully adapted to their habits of life û for instance, a woodpecker or a tree_frog to climb trees, or a seed for dispersal by hooks or plumes. I had always been much struck by such adaptation, and until these could be explained it seemed to me almost useless to endeavor to prove by indirect evidence that species have been modified.
        After my return to England it appeared to me that by the following example of [Sir Charles] Lyell in geology, and by collecting all facts which bore in any way on the variation of animals and plants under domestication and nature, some light might perhaps be thrown on the whole subject. My first notebook was opened in July 1837. I worked on true Baconian principles [i.e., following the scientific method of Francis Bacon] and without any theory collected facts on a wholesale scale, more especially with respect to domesticated productions, by printed enquiries, by conversation with skillful breeders and gardeners, and by extensive reading. When I see the list of books of all kinds which I read and abstracted, . . . I am surprised at my industry. I soon perceived that selection was the keystone of mans success in making useful races of animals and plants. But how selection could be applied to organisms living in a state of nature remained for some time a mystery to me.
        In October 1838, that is, fifteen months after I had begun my systematic enquiry, I happened to read for amusement [Thomas] Malthus on Population, and being well prepared to appreciate the struggle for existence which everywhere goes on from long_continued observation of the habits of animals and plants, it at once struck me that under these circumstances favorable variations would tend to be preserved and unfavorable ones to be destroyed. The result of this would be the formation of new species. Here, then, I had at last got a theory by which to work. . . .
        My Descent of Man was published in February 1871. As soon as I had become, in the year 1837 or 1838, convinced that species were mutable productions, I could not avoid the belief that man must come under the same law.

Owing to this struggle [for existence], variations, however slight . . . , if they be in any degree profitable to the individuals of a species, in their infinitely complex relations to other organic beings and to their physical conditions of life, will tend to the preservation of such individuals, and will generally be inherited by the offspring. The offspring, also, will thus have a better chance of surviving, for, of the many individuals of any species which are periodically born, but a small number can survive. I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection, in order to mark its relation to mans power of selection. But the expression often used by Mr. Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient. . . .
        A struggle for existence inevitably follows from the high rate at which all organic beings tend to increase. Every being, which during its natural lifetime produces several eggs or seeds, must suffer destruction during some period of its life, and during some season or occasional year, otherwise, on the principle of geometrical increase, its numbers would quickly become so inordinately great that no country could support the product. Hence, as more individuals are produced than can possibly survive, there must in every case be a struggle for existence, either one individual with another of the same species, or with the individuals of distinct species, or with the physical conditions of life. It is the doctrine of Malthus applied with manifold force to the whole animal and vegetable kingdoms; for in this case there can be no artificial increase of food, and no prudential restraint from marriage. Although some species may be now increasing, more or less rapidly, in numbers, all cannot do so, for the whole world would not hold them.
        There is no exception to the rule that every organic being naturally increases at so high a rate, that, if not destroyed, the earth would soon be covered by the progeny of a single pair. Even slow_breeding man has doubled in twenty_five years, and at this rate, in less than a thousand years, there would literally not be standing room for his progeny. . . . The elephant is reckoned the slowest of all known animals, and I have taken some pains to estimate its probable minimum rate of natural increase; it will be safest to assume that it begins breeding when thirty years old, and goes on breeding till ninety years old, bringing forth six young in the interval, and surviving till one hundred years old; if this be so, after a period of from 740 to 750 years there would be nearly nineteen million elephants alive, descended from the first pair. . . .
        Can we doubt (remembering that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favorable individual differences and variations, and the destruction of those which are injurious, I have called Natural Selection, or the Survival of the Fittest. . . .
        Natural Selection acts solely through the preservation of variations in some way advantageous, which consequently endure. Owing to the high geometrical rate of increase of all organic beings, each area is already fully stocked with inhabitants; and it follows from this, that as the favored forms increase in number, so, generally, will the less favored decrease and become rare. . . .
        From these several considerations I think it inevitably follows, that as new species in the course of time are formed through natural selection, others will become rarer and rarer, and finally extinct. The forms which stand in closest competition with those undergoing modification and improvement will naturally suffer most. And we have seen in the chapter on the Struggle for Existence that it is the most closely allied forms- varieties of the same species, and species of the same genus or of related genera - which, from having nearly the same structure, constitution, and habits, generally come into the severest competition with each other. Consequently, each new variety or species, during the progress of its formation, will generally press hardest on its nearest kindred, and tend to exterminate them. We see the same process of extermination amongst our domesticated productions, through the selection of improved forms by man.

The Descent of Man

The main conclusion here arrived at, and now held by many naturalists who are well competent to form a sound judgment, is that man is descended from some less highly organized form. The grounds upon which this conclusion rests will never be shaken, for the close similarity between man and the lower animals in embryonic development, as well as in innumerable points of structure and constitution, both of high and of the most trifling importance . . . are facts which cannot be disputed. They have long been known, but until recently they told us nothing with respect to the origin of man. Now when viewed by the light of our knowledge of the whole organic world, their meaning is unmistakable. The great principle of evolution stands up clear and firm, when these groups of facts are considered in connection with others, such as the mutual affinities of the members of the same group, their geographical distribution in past and present times, and their geological succession. It is incredible that all these facts should speak falsely. He who is not content to look . . . at the phenomena of nature as disconnected, cannot any longer believe that man is the work of a separate act of creation. He will be forced to admit that the close resemblance of the embryo of man to that, for instance, of a dog û the construction of his skull, limbs, and whole frame on the same plan with that of other mammals, independently of the uses to which the parts may be put . . . and a crowd of analogous facts û all point to the conclusion that man is the co_descendant with other mammals of a common progenitor.
        We have seen that man incessantly presents individual differences in all parts of his body and in his mental faculties. These differences or variations seem to be induced by the same general causes, and to obey the same laws as with the lower animals. In both cases similar laws of inheritance prevail. Man tends to increase at a greater rate than his means of subsistence; consequently he is occasionally subjected to a severe struggle for existence, and natural selection will have effected whatever lies within its scope. A succession of strongly marked variations of a similar nature is by no means requisite; slight fluctuating differences in the individual suffice for the work of natural selection. . .
        Man may be excused at feeling some pride for having risen, though not through his own exertions, to the very summit of the organic scale; and the fact of his having thus risen, instead of [his] having been originally placed there, may give him hope for a still higher destiny in the distant future. But we are not here concerned with hopes or fears, only with truth as far as our reason permits us to discover it; and I have given the evidence to the best of my ability.
We must, however, acknowledge, as it seems to me, that man with all his noble qualities, with [the] sympathy he feels for the most debased, with [the] benevolence which extends not only to other men but to the humblest living creature, with his god_like intellect which has penetrated into the movements and constitution of the solar system, . . . [yet] man still bears in his bodily frame the indelible stamp of his lowly origin.