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Darwin Correspondence Project

To August Weismann   5 April 1872

Down, Beckenham, Kent

April 5th. 1872

My dear Sir

I have now read your essay with very great interest.1 Your view of the origin of local races through “amixie” is altogether new to me, and seems to throw an important light on an obscure problem.2 There is however something strange about the periods or endurance or variability.3 I formerly endeavoured to investigate the subject, not by looking to past time, but to species of the same genus widely distributed; and I found in many cases that all the species, with perhaps one or two exceptions, were variable. It would be a very interesting subject for a conchologist to investigate, viz: whether the species of the same genus were variable during many successive geological formations. I began to make enquiries on this head, but failed in this, as in so many other things, from the want of time and strength. In your remarks on crossing you do not, as it seems to me, lay nearly stress enough on the increased vigour of the offspring derived from parents which have been exposed to different conditions. I have during the last 5 years been making experiments on this subject with plants, and have been astonished at the results, which have not yet been published.4

In the first part of your essay I thought that you wasted (to use an English expression) too much powder and shot on M. Wagner; but I changed my opinion when I saw how admirably you treated the whole case, and how well you used the facts about the Planorbis.5 I wish I had studied this latter case more carefully. The manner in which, as you show, the different varieties blend together and make a constant whole, agrees perfectly with my hypothetical illustrations6

Many years ago the late E. Forbes described three closely consecutive beds in a Secondary formation, each with representative forms of the same fresh water shells: the case is evidently analogous with that of Hilgendorf, but the interesting connecting varieties or links were here absent.7 I rejoice to think that I formerly said as emphatically as I could, that neither isolation nor time by themselves do anything for the modification of species.8 Hardly anything in your essay has pleased me so much personally, as to find that you believe to a certain extent in sexual selection.9 As far as I can judge, very few naturalists believe in this. I may have erred on many points, and extended the doctrine too far, but I feel a strong conviction that sexual selection will hereafter be admitted to be a powerful agency. I cannot agree with what you say about the taste for beauty in animals not easily varying.10 It may be suspected that even the habit of viewing differently coloured surrounding objects would influence their taste, and Fritz Müller even goes so far as to believe that the sight of gaudy butterflies might influence the taste of distinct species.11 There are many remarks and statements in your essay which have interested me greatly, and I thank you for the pleasure which I have received from reading it.

With sincere respect, I remain | My dear Sir | Yours very faithfully | Charles Darwin

If you should ever be induced to consider the whole doctrine of sexual selection, I think that you will be led to the conclusion that characters thus gained by one sex are very commonly transferred in a greater or less degree to the other sex.12


CD had received Weismann’s essay on the influence of isolation on the formation of species (Weismann 1872) in February 1872 (see letter to August Weismann, 29 February 1872 and n. 3).
Weismann coined the term Amixie to refer to the total prevention of crossing between two populations due to isolation (Weismann 1872, p. 49 n. 3). Weismann argued that Amixie did not necessarily result in the formation of new species and conversely that Amixie was not a necessary requirement in the formation of new species. He cited examples to illustrate his argument (ibid., pp. 49–51).
Weisman hypothesised that populations experienced periods of increased variability interspersed with longer periods of constancy and argued that periods of variability could be triggered by changes in external conditions. Isolation was only one sort of change that might be encountered (Weismann 1872, pp. 51–2).
CD refers to his research on successive generations of cross-fertilised and self-fertilised plants, published in Cross and self fertilisation in 1876.
Moritz Wagner had argued that a population had to be isolated geographically in order to form new species (Wagner 1868a, 1868b, and 1870). Using successive varieties of a ram’s horn snail referred to as Planorbis multiformis, Weismann argued that new species could form without being isolated from the parent species (Weismann 1872, p. 15). Ram’s horn snails are freshwater pulmonate gastropods; the species referred to as P. multiformis are now in the genus Gyraulus; see Nützel and Bandel 1993, p. 318).
In Origin 5th ed., p. 362, in his discussion of the absence of intermediate varieties, CD mentioned only briefly Franz Hilgendorf’s discovery of the series of forms described as Planorbis multiformis (Hilgendorf 1866). Later in the same section (ibid., pp. 366–7), CD presented a hypothetical case of successive species found in different strata in order to show the difficulty of determining intermediate varieties that originated from a common progenitor.
Edward Forbes had described different forms of the same genera of freshwater gastropods in three distinct strata in his preliminary report on the strata and organic remains in the Dorsetshire Purbecks (Forbes 1850, pp. 80–1).
See Origin, pp. 105–9.
Weismann argued that sexual selection could influence the formation of new species (Weismann 1872, pp. 72–4); he assigned sexual selection a secondary role in evolution, a role which was not dependent on environmental influences, but which could increase the amount of variability in a species (ibid., pp. 61–2; see also Marginalia 1: 859 for CD’s comments on some of Weismann’s points on the role of sexual selection).
Weismann argued that even if populations became isolated, the preference or taste for a certain appearance in the opposite sex would remain constant (Weismann 1872, p. 70).
See Correspondence vol. 19, letter from Fritz Müller, 14 June 1871. Müller had suggested that females of one species might be attracted to the bright colours of males of another species, and that consequently males of the first species might start to resemble those of the second species.
See Descent 2: 18, 23, and 46 ff.


Comments on AW’s work [Einfluss der Isolierung (1872)].

Discusses formation of local races.

Conchologist should investigate whether species of same genus vary during successive geological periods.

Comments on Franz Hilgendorf ["Über Planorbis multiformis", Monatsber. K. Preuss. Akad. Wiss. Berlin (1866): 474–504].

Believes sexual selection will be judged a powerful agency.

Letter details

Letter no.
Charles Robert Darwin
Leopold Friedrich August (August) Weismann
Sent from
Source of text
DAR 148: 343
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 8275,” accessed on 21 June 2018,

Also published in The Correspondence of Charles Darwin, vol. 20