My dear and most honoured Sir,

I am very much honoured by your extreme kindness to send me a copy of your lately published book: the descent of Man, and Selection in relation to Sex.¹ My intention was to read it immediately and to thank you in the same time for the book and for the instruction. But I see, that it will last some time more, before my occupations, which very often increase unexpectedly, allow me, to read and to study the book as it should be done.

I always took a great interest in the question of the origin of the organised beeings. Even in 1847 I wrote and published an essay (oratio inauguralis) on the subject: Harmony of animal life a manifestation of laws,²—containing, from the physiological point de vue, a further development of the doctrine, which had been indicated by Lamarck,³ although the communications, on this subject, of Lamarck were as unknown to me as almost to every one, in that period. Fully excluding the final causes from scientifical research and theory, I tried to show, how the infinite harmonical relations, at the one side, between the animals and the surrounding nature, at the other side, between the different parts and organs of every organism, are to be deduced from the laws of adaptation by habitude and by exercise and from the laws of transmission. I applied the same on the psychical actions. I admitted the gradual evolution of the highest orders of plants and animals from mere simple forms of spontaneous origin, and the origin of different species from the same source. I indicated the changes, which are obtained by artificial selection, found the cause of continual progress in the circumstance, that every not wel adapted form necessarily is condemned to perish, but still was not aware of the influence of natural selection,—your great and immortal discovery, the mighty factor, which alone allowed to give a full and special demonstration of the theory of descent.

As I began to write, I had not the intention, to mention to you my little book, but telling about my special interests in the subject, I rather involuntarily felt inclined to explain it. And now, although it is written in Dutch, I could not resist to my wish to send you a copy, in the hope that you will benevolently accept it.—⁴

Will you kindly offer my respects to Mistr. Darwin⁵ and your dear family. I am, Sir, with profound esteem your very obedient Donders