It was crucial to Darwin’s theories of species change that naturally occurring variations could be inherited. But at the time when he wrote Origin, he had no explanation for how inheritance worked – it was just obvious that it did. Darwin’s attempt to describe how heredity might work, his 'provisional hypothesis of Pangenesis’, was published in 1868 in his book, Variation of animals and plants under domestication
The year 1871 was an extremely busy and productive one for Darwin, with the publication in February of his long-awaited book on human evolution, Descent of man. The other main preoccupation of the year was the preparation of his manuscript on expression. Darwin continued to investigate the mechanisms of various emotions, such as grief, shame, and astonishment, drawing on the expertise of physicians and physiologists, as well as zoo-keepers, pet owners, parents of young children, and professional photographers. The year also brought a significant milestone for the family, as Darwin’s eldest daughter Henrietta was married in August.
Charles Darwin’s major achievement in 1867 was the completion of his large work, The variation of animals and plants under domestication (Variation). The importance of Darwin’s network of correspondents becomes vividly apparent in his work on expression in 1867, as he continued to circulate a list of questions on human expression that he may have drawn up in late 1866. His correspondents were asked to copy the list and forward it to those who might best answer the questions, with the result that Darwin began to receive replies from different corners of the world.
Glad THH has taken up aphid question versus Owen ["On the agamic reproduction and morphology of Aphis", Trans. Linn. Soc. Lond. 22 (1858): 193–236].
Fertilisation and inheritance discussed. Speculates that fertilisation may be a mixture rather than a fusion. Can understand in no other way why crossed forms tend to go back to ancestral forms.
Confirms CGBD’s impression given in a letter to J. S. Henslow that CD in the Origin did not touch directly upon the final causes of sexuality, which CD considers one of the "profoundest mysteries in nature". CD is inclined to stress sexuality as the means of keeping forms constant and checking variation although he grants its role in the origination of varieties. [See 2869.]
His thanks for the pamphlet ["Remarks on the final causes of the sexuality of plants" (1860)] and the extremely kind and liberal manner in which Daubeny alludes to CD’s work.
Further discussion of sexual generation and CD’s suspicion that its most important function remains hidden.
Pleased that Bentham is cautious about Naudin’s view of reversion. CD can show experimentally that crossing of races and species tends to bring back ancient characters.
Suggests Gärtner’s Bastarderzeugung [1849] be translated
and that Oliver review Scott’s Primula paper [J. Linn. Soc. Lond. (Bot.) 8 (1865): 78–126] for a future issue of Natural History Review.
He has finished MEW’s work on hybrid willows [Die Bastardbefruchtung im Planzenreich (1865)] and sends his thanks. The extreme frequency of hybrid willows is new to CD, and he finds the explanation of their numbers in certain locations ingenious.
Comments on the criticism of Gärtner’s view of reversion
and the differences between MEW and Naudin.
CD now has doubts regarding his own view that hybrids are sterile from not being perfectly accommodated to their conditions of life.
Thanks for THH’s willingness to read Pangenesis MS. Thinks some such view will have to be adopted but it overthrows, in an uncomfortable manner, ordinary development.
