(257/2. In the fifth edition of the "Origin" (page 362), however, Darwin speaks of the graduated forms of Planorbis multiformis, described by Hilgendorf from certain beds in Switzerland, by which we presume he meant the Steinheim beds in Wurtemberg.) The variability of these shells is quite astonishing, and seems to exceed that of Rubus or Hieracium amongst plants. The result which surprises me most is that the same form should be developed from various and different progenitors. This seems to show how potent are the conditions of life, irrespectively of the variations being in any way beneficial.
The production of a species out of a chaos of varying forms reminds me of Nageli's conclusion, as deduced from the study of Hieracium, that this is the common mode in which species arise. But I still continue to doubt much on this head, and cling to the belief expressed in the first edition of the "Origin," that protean or polymorphic species are those which are now varying in such a manner that the variations are neither advantageous nor disadvantageous. I am glad to hear of the Brunswick deposit, as I feel sure that the careful study of such cases is highly important. I hope that the Smithsonian Institution will publish your memoir.
LETTER 258. TO A. DE CANDOLLE. Down, January 18th [1873].
It was very good of you to give up so much of your time to write to me your last interesting letter. The evidence seems good about the tameness of the alpine butterflies, and the fact seems to me very surprising, for each butterfly can hardly have acquired its experience during its own short life. Will you be so good as to thank M. Humbert for his note, which I have been glad to read. I formerly received from a man, not a naturalist, staying at Cannes a similar account, but doubted about believing it. The case, however, does not answer my query--viz., whether butterflies are attracted by bright colours, independently of the supposed presence of nectar?
I must own that I have great difficulty in believing that any temporary condition of the parents can affect the offspring. If it last long enough to affect the health or structure of the parents, I can quite believe the offspring would be modified. But how mysterious a subject is that of generation! Although my hypothesis of pangenesis has been reviled on all sides, yet I must still look at generation under this point of view; and it makes me very averse to believe in an emotion having any effect on the offspring. Allow me to add one word about blushing and shyness: I intended only to say the habit was primordially acquired by attention to the face, and not that each shy man now attended to his personal appearance.
LETTER 259. TO J.D. HOOKER. Down, June 28th, 1873.
I write a line to wish you good-bye, as I hear you are off on Wednesday, and to thank you for the Dionoea, but I cannot make the little creature grow well. I have this day read Bentham's last address, and must express my admiration of it. (259/1. Presidential address to the Linnean Society, read May 24th, 1873.) Perhaps I ought not to do so, as he fairly crushes me with honour.
I am delighted to see how exactly I agree with him on affinities, and especially on extinct forms as illustrated by his flat-topped tree. (259/2. See page 15 of separate copy: "We should then have the present races represented by the countless branchlets forming the flat-topped summit" of a genealogical tree, in which "all we can do is to map out the summit as it were from a bird's-eye view, and under each cluster, or cluster of clusters, to place as the common trunk an imaginary type of a genus, order, or class according to the depth to which we would go.") My recent work leads me to differ from him on one point--viz., on the separation of the sexes. (259/3. On the question of sexuality, see page 10 of Bentham's address. On the back of Mr. Darwin's copy he has written: "As long as lowest organisms free--sexes separated: as soon as they become attached, to prevent sterility sexes united--reseparated as means of fertilisation, adapted [?] for distant [?] organisms,--in the case of animals by their senses and voluntary movements,--with plants the aid of insects and wind, the latter always existed, and long retained." The two words marked [?] are doubtful.