In 1874, St George Jackson Mivart caused Darwin and his son George serious offence. Mivart had previously been a correspondent of CD's, but had written hostile reviews of some of CD's work, as a result of which CD had brought their correspondence to an end. The dispute was not resolved until early 1875, and, even then, not to Darwin's complete satisfaction. The story sheds light on CD's anxiety about the respectability of his views and the views of those associated with him, his reluctance to enter a public debate, the fierce loyalty of his friends, and contemporary codes of behaviour in scientific society. It has been discussed in Gruber 1960, pp. 98–114, and Dawson 2007, pp. 77–81.

In August 1873, George had published an article under the title ‘On beneficial restrictions to liberty of marriage’ in the Contemporary Review (G. H. Darwin 1873b). In this article, George discussed how modern scientific doctrines might be expected in the future to affect personal liberty in the matter of marriage. A better understanding of the inheritance of mental and physical qualities would make people realise that their reproductive choices would have an effect on future society. Francis Galton had written about the possibility of creating an elite who would intermarry as a way of improving the race; George wanted to discuss the consequences of a scheme he thought more likely to be adopted, the prevention of marriage among inferior members of the race. Mental disease seemed to be increasing, and in his view was inheritable, and the most obvious way to deal with it was to introduce restrictions on marriage.

As a first step, he argued, a divorce should not be refused on the grounds of the insanity of either party. The next step would be that insanity should itself be grounds for divorce: ‘as … no slur would be cast on the character of either party, the divorce proceedings would lose much of their sting, and the patient, should he recover, would suffer in no other respect than does anyone, who is forced by ill-health to retire from any career which has been begun; although, of course, the necessary isolation of the parent from the children would be a peculiarly bitter blow’ (p. 418).

The year 1874 was one of consolidation, reflection, and turmoil for Darwin. He spent the early months working on second editions of Coral reefs and Descent of man; the rest of the year was mostly devoted to further research on insectivorous plants. A vicious dispute over an anonymous review that attacked the work of Darwin's son George dominated the second half of the year. When requested to provide words to celebrate what would have been the naturalist and traveller Alexander von Humboldt's 105th birthday, Darwin obliged with a reflection on his debt to Humboldt, whom he had greatly admired in his youth: ‘I have always looked on him as one of the greatest men the world has ever produced. He gave a wonderful impetus to science by showing what could be done by observation during prolonged intervals' (letter to D. T. Gardner, [c. 27 August 1874]). The death of a Cambridge friend, Albert Way, caused Darwin's cousin, William Darwin Fox, to reminiscence about their university days together, and the long-abandoned pleasures of shooting and collecting beetles (letter from W. D. Fox, 8 May [1874]). Such reminiscences led Darwin to the self-assessment, ‘as for one's body growing old there is no help for it, & I feel as old as Methusalem; but not much in mind except that I think one takes everything more quietly, as not signifying so much. And … one looks backwards much more than forwards' (letter to W. D. Fox, 11 May [1874]).

The year started for Darwin with a week's visit to London, staying at his brother Erasmus's house. He requested a visit from his doctor, Andrew Clark, whom he had been consulting since August 1873. Darwin had originally thought that Clark's dietary treatment would ‘do wonders’, but as he confessed to his old Beagle shipmate Bartholomew James Sulivan, ‘it was an illusory hope.— I feel very old & helpless’ (letter to B. J. Sulivan, 6 January [1874]). Darwin mentioned his poor health so frequently in correspondence that Ernst Haeckel inferred that he was well from his silence on the matter (letter from Ernst Haeckel, 26 October 1874).