With respect to your objection of a multitude of still living simple forms, I have not discussed it anywhere in the "Origin," though I have often thought it over. What you say about progress being only occasional and retrogression not uncommon, I agree to; only that in the animal kingdom I greatly doubt about retrogression being common. I have always put it to myself--What advantage can we see in an infusory animal, or an intestinal worm, or coral polypus, or earthworm being highly developed? If no advantage, they would not become highly developed: not but what all these animals have very complex structures (except infusoria), and they may well be higher than the animals which occupied similar places in the economy of nature before the Silurian epoch. There is a blind snake with the appearances and, in some respects, habits of earthworms; but this blind snake does not tend, as far as we can see, to replace and drive out worms. I think I must in a future edition discuss a few more such points, and will introduce this and H.C. Watson's objection about the infinite number of species and the general rise in organisation. But there is a directly opposite objection to yours which is very difficult to answer--viz. how at the first start of life, when there were only the simplest organisms, how did any complication of organisation profit them? I can only answer that we have not facts enough to guide any speculation on the subject.
With respect to Lepidosiren, Ganoid fishes, perhaps Ornithorhynchus, I suspect, as stated in the "Origin," (95/7. "Origin of Species" (Edition VI.), page 83.), that they have been preserved, from inhabiting fresh-water and isolated parts of the world, in which there has been less competition and less rapid progress in Natural Selection, owing to the fewness of individuals which can inhabit small areas; and where there are few individuals variation at most must be slower. There are several allusions to this notion in the "Origin," as under Amblyopsis, the blind cave-fish (95/8. "Origin," page 112.), and under Heer (95/9. "Origin," page 83.) about Madeira plants resembling the fossil and extinct plants of Europe.
LETTER 96. TO JAMES LAMONT. Down, March 5th [1860?].
I am much obliged for your long and interesting letter. You have indeed good right to speak confidently about the habits of wild birds and animals; for I should think no one beside yourself has ever sported in Spitzbergen and Southern Africa. It is very curious and interesting that you should have arrived at the conclusion that so-called "Natural Selection" had been efficient in giving their peculiar colours to our grouse. I shall probably use your authority on the similar habits of our grouse and the Norwegian species.
I am particularly obliged for your very curious fact of the effect produced by the introduction of the lowland grouse on the wildness of the grouse in your neighbourhood. It is a very striking instance of what crossing will do in affecting the character of a breed. Have you ever seen it stated in any sporting work that game has become wilder in this country? I wish I could get any sort of proof of the fact, for your explanation seems to me equally ingenious and probable. I have myself witnessed in South America a nearly parallel [case] with that which you mention in regard to the reindeer in Spitzbergen, with the Cervus campestris of La Plata. It feared neither man nor the sound of shot of a rifle, but was terrified at the sight of a man on horseback; every one in that country always riding. As you are so great a sportsman, perhaps you will kindly look to one very trifling point for me, as my neighbours here think it too absurd to notice --namely, whether the feet of birds are dirty, whether a few grains of dirt do not adhere occasionally to their feet. I especially want to know how this is in the case of birds like herons and waders, which stalk in the mud. You will guess that this relates to dispersal of seeds, which is one of my greatest difficulties.