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