Only a few women wrote to Darwin about overtly feminist topics, but many of his female correspondents were involved with the suffrage movement and the promotion of women's education. Often they were also involved in the campaign against vivisection; for some, as for Frances Power Cobbe, female emancipation and protection of animals went hand in hand, both women and animals suffering under a malign social order. Such campaigners often felt that Darwinian theory was on their side. Darwin's books had stressed the continuity of humans with the rest of the animal kingdom, so that it was not feasible for Darwinians to see animals as soulless machines that only appeared to feel pain, as Cartesian philosophy suggested. Also, whatever his own political and personal preferences, his account of female subordination made it seem contingent upon historical circumstances: it could, in theory, be changed.

It's also clear from family letters that women in Darwin's family, and their friends, were very aware of contemporary debates about feminism. Some of them were involved in the setting up of Newnham and Girton Colleges at Cambridge. Henrietta found herself smoking cigarettes with the Stansfelds, well-known feminist campaigners, in France. She had discussions with her friends about what they really wanted from education: was what men had really the ideal? Women in their circle, even without raising any particular banner, were extraordinarily active: they learnt mathematics and physics; they hired tutors; they took examinations; they watched debates in the House of Commons from the ladies’ gallery; they attended university lectures if they were open to women.

Darwin himself was reticent on the subject. However, the surprisingly effective combination of women and opposition to vivisection spurred him to become a pragmatic supporter of scientific education for women. Women, with the moral authority resulting from their subordination and their motherly role, were effective advocates for an anti-vivisection law, even without the vote. Darwin lamented that if only they understood the medical benefits of physiological research, they would take a more moderate position. When the tricky subject arose of whether girls should learn physiology, he said they certainly should, if they wanted to. Possibly the drip-feed of barely voiced feminism that he had been receiving from his correspondence also had an effect.