(249/1. Here follows the extract from the "Origin," sixth edition, page 51: "The elephant is reckoned the slowest breeder 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." In the fifth edition, page 75, the passage runs: "If this be so, at the end of the fifth century, there would be alive fifteen million elephants, descended from the first pair" (see "Athenaeum," June 5, July 3, 17, 24, 1869).)
LETTER 250. TO C. LYELL. Down, May 10th .
I received yesterday morning your present of that work to which I, for one, as well as so many others, owe a debt of gratitude never to be forgotten. I have read with the greatest interest all the special additions; and I wish with all my heart that I had the strength and time to read again every word of the whole book. (250/1. "Principles of Geology," Edition XII., 1875.) I do not agree with all your criticisms on Natural Selection, nor do I suppose that you would expect me to do so. We must be content to differ on several points. I differ must about your difficulty (page 496) (250/2. In Chapter XLIII. Lyell treats of "Man considered with reference to his Origin and Geographical Distribution." He criticizes the view that Natural Selection is capable of bringing about any amount of change provided a series of minute transitional steps can be pointed out. "But in reality," he writes, "it cannot be said that we obtain any insight into the nature of the forces by which a higher grade of organisation or instinct is evolved out of a lower one by becoming acquainted with a series of gradational forms or states, each having a very close affinity with the other."..."It is when there is a change from an inferior being to one of superior grade, from a humbler organism to one endowed with new and more exalted attributes, that we are made to feel that, to explain the difficulty, we must obtain some knowledge of those laws of variation of which Mr. Darwin grants that we are at present profoundly ignorant" (op. cit., pages 496-97).) on a higher grade of organisation being evolved out of lower ones. Is not a very clever man a grade above a very dull one? and would not the accumulation of a large number of slight differences of this kind lead to a great difference in the grade of organisation? And I suppose that you will admit that the difference in the brain of a clever and dull man is not much more wonderful than the difference in the length of the nose of any two men. Of course, there remains the impossibility of explaining at present why one man has a longer nose than another. But it is foolish of me to trouble you with these remarks, which have probably often passed through your mind. The end of this chapter (XLIII.) strikes me as admirably and grandly written. I wish you joy at having completed your gigantic undertaking, and remain, my dear Lyell,
Your ever faithful and now very old pupil, CHARLES DARWIN.
LETTER 251. TO J. TRAHERNE MOGGRIDGE. Sevenoaks, October 9th .
I have just received your note, forwarded to me from my home. I thank you very truly for your intended present, and I am sure that your book will interest me greatly. I am delighted that you have taken up the very difficult and most interesting subject of the habits of insects, on which Englishmen have done so little. How incomparably more valuable are such researches than the mere description of a thousand species! I daresay you have thought of experimenting on the mental powers of the spiders by fixing their trap-doors open in different ways and at different angles, and observing what they will do.
We have been here some days, and intend staying some weeks; for I was quite worn out with work, and cannot be idle at home.
I sincerely hope that your health is not worse.