Darwin, in The Variation of Animals and Plants Under Domestication, volume 2, pp. 248-249.
Throughout this chapter and elsewhere I have spoken of selection as the paramount power, yet its action absolutely depends on what we in our ignorance call spontaneous or accidental variability. Let an architect be compelled to build an edifice with uncut stones, fallen from a precipice. The shape of each fragment may be called accidental; yet the shape of each has been determined by the force of gravity, the nature of the rock, and the slope of the precipice,—events and circumstances, all of which depend on natural laws; but there is no relation between these laws and the purpose for which each fragment is used by the builder. In the same manner the variations of each creature are determined by fixed and immutable laws; but these bear no relation to the living structure which is slowly built up through the power of selection, whether this be natural or artificial selection.
If our architect succeeded in rearing a noble edifice, using the rough wedge-shaped fragments for the arches, the longer stones for the lintels, and so forth, we should admire his skill even in a higher degree than if he had used stones shaped for the purpose. So it is with selection, whether applied by man or by nature; for though variability is indispensably necessary, yet, when we look at some highly complex and excellently adapted organism, variability sinks to a quite subordinate position in importance in comparison with selection, in the same manner as the shape of each fragment used by our supposed architect is unimportant in comparison with his skill.
Darwin, in the sixth edition of the Origin of Species, pp. 421-422:
I see no good reason why the views given in this volume should shock the religious feelings of any one. It is satisfactory, as showing how transient such impressions are, to remember that the greatest discovery ever made by man, namely, the law of the attraction of gravity, was also attacked by Leibnitz, "as subversive of natural, and inferentially of revealed, religion." A celebrated author and divine has written to me that "he has gradually learnt to see that it is just as noble a conception of the Deity to believe that He created a few original forms capable of self-development into other and needful forms, as to believe that He required a fresh act of creation to supply the voids caused by the action of His laws."
Darwin, in The Descent of Man, volume 1, pp. 26-27:
It appears as if the posterior molar or wisdom-teeth were tending to become rudimentary in the more civilised races of man. These teeth are rather smaller than the other molars, as is likewise the case with the corresponding teeth in the chimpanzee and orang; and they have only two separate fangs. They do not cut through the gums till about the seventeenth year, and I am assured by dentists that they are much more liable to decay, and are earlier lost, than the other teeth. It is also remarkable that they are much more liable to vary both in structure and in the period of their development than the other teeth. In the Melanian races, on the other hand, the wisdom-teeth are usually furnished with three separate fangs, and are generally sound: they also differ from the other molars in size less than in the Caucasian races. Prof. Schaaffhausen accounts for this difference between the races by "the posterior dental portion of the jaw being always shortened" in those that are civilised, and this shortening may, I presume, be safely attributed to civilised men habitually feeding on soft, cooked food, and thus using their jaws less. I am informed by Mr. Brace that it is becoming quite a common practice in the United States to remove some of the molar teeth of children, as the jaw does not grow large enough for the perfect development of the normal number.
Darwin, in the sixth edition of the Origin of Species, p. 421:
[A]s my conclusions have lately been much misrepresented, and it has been stated that I attribute the modification of species exclusively to natural selection, I may be permitted to remark that in the first edition of this work, and subsequently, I placed in a most conspicuous position—namely, at the close of the Introduction—the following words: "I am convinced that natural selection has been the main but not the exclusive means of modification." This has been of no avail. Great is the power of steady misrepresentation; but the history of science shows that fortunately this power does not long endure.
(mentioned in Branch G, Scott EC. 2008. The latest face of creationism. Sci Am 300(1):92-99.)
Darwin, in The Expression of Emotion in Man and Animals, p. 222-223, referring to the muscles involved in furrowing the brow during a frown:
It is not surprising that the corrugators should have become much more developed in man than in the anthropoid apes; for they are brought into incessant action by him under various circumstances, and will have been strengthened and modified by the inherited effects of use.... When the eyes are closed as quickly and as forcibly as possible, to save them from being injured by a blow, the corrugators contract. With savages or other men whose heads are uncovered, the eyebrows are continually lowered and contracted to serve as a shade against a too strong light; and this is effected partly by the corrugators. This movement would have been more especially serviceable to man, as soon as his early progenitors held their heads erect.
Interesting because (a) it's one of his clearer references to use inheritance; (b) it's a clear statement of comparative evolutionary anatomy applied to behavior, and (c) it presaged Grover Krantz by 100 years.
"I brought my baby to touch the wall, so that the power of Darwin can purify her genetic makeup of undesirable inherited traits," said Darlene Freiberg, one among a growing crowd assembled here to see the mysterious stain, which appeared last Monday on one side of the Rhea County Courthouse. The building was also the location of the famed "Scopes Monkey Trial" and is widely considered one of Darwinism's holiest sites. "Forgive me, O Charles, for ever doubting your Divine Evolution. After seeing this miracle of limestone pigmentation with my own eyes, my faith in empirical reasoning will never again be tested."
Jonah Lehrer went in to WALL-E (an enormously entertaining movie) and came out thinking of Darwin's Expression of Emotion in Man and Animals:
The emotional brain is actually the most ancient part of our cortical machinery, a piece of hardware that's been refined by evolution over the last several hundred million years. That's why, as Darwin pointed out, animals that are utterly lacking in self-awareness - he called them "creatures of pure instinct" - tend to express their emotions in the same manner as humans. Even more radically, Darwin suggested that these expressions were evidence that the animals were also experiencing emotion, even though they were just obeying some ancient biological drives.
Lehrer's recent book is Proust Was a Neuroscientist.
A propos to my post earlier this week about reading science in English class, Olivia Judson devotes her weekly blog entry to the question, "Was Darwin a good science writer?" No surprise, she thinks he was, despite certain dense sections, of the Origin.
Judson describes the confessionals of professional biologists who never read the founding work of evolutionary biology. I'm less concerned: Much of the Origin is hard to read, and many biology students would be better served reading a modern exegesis. I would be more interested in seeing students read a good selection of excerpts of Darwin's other works, especially the Voyage of the Beagle, and I'd like to see letter exchanges included as examples of scientific and literary correspondence.
Don't get me wrong: Both the Origin and the Descent of Man (both freely available from Darwin Online) reward close reading. As do many other dense works, including Fisher's Genetical Theory and Lotka's Elements of Physical Biology. But they're college-level works, no doubt, and not everyone's cup of tea.