The year is established by the year of publication of the letter in Nature, 6 July 1871.

Henry Hoyle Howorth’s letter was published under the heading ‘A new view of Darwinism’ on 29 June 1871 (Howorth 1871). Howorth claimed that the theory of natural selection implied ‘the Survival of the Stronger’, rather than merely the survival of the fittest, which he took to be a tautology. However, he gave several examples in which animals and plants were highly fertile when they were not otherwise in vigorous health, and argued, ‘far from the strong surviving the weak, the tendency among the strong, the well fed, and highly favoured, is to decay, become sterile and die out, while the weak, the under-fed, and the sickly are increasing at a proportionate rate.’

In his letter to Nature, Howorth had credited Thomas Doubleday with showing that humans suffered decreased fertility when they had a rich diet and a luxurious lifestyle, ‘while the poor, under-fed, and hard-worked’ were very fertile. Howorth was probably referring to Doubleday’s The true law of population shewn to be connected with the food of the people (Doubleday 1843, especially chapters 2 and 9 and the Postscript to the second edition). CD had read Doubleday 1842 (the first edition of True law of population) in 1843 (see CD’s reading notebooks (Correspondence vol. 4, Appendix IV, 119: 13a)). CD also refers to Variation 2: 111–13, 148–65.