Our only protection from so admirable a sister-in-law is in her working him too hard." He commented, "She already takes him to task about his idleness — She is going some day to explain to him her notions about marriage — Perfect equality of rights is part of her doctrine. I much doubt whether it will be equality in practice.The Darwins shared Martineau's Unitarian background and Whig politics, but their father Robert was concerned that, as a potential daughter-in-law, she was too extreme in her politics. Charles noted that his father was upset by a piece in the "Westminster Review" calling for the radicals to break with the Whigs and give working men the vote "before he knew it was not [Martineau's], and wasted a good deal of indignation, and even now can hardly believe it is not hers". In early December 1836 Charles Darwin called on Martineau and may have discussed the social and natural worlds she was writing about in her book "Society in America", including the "grandeur and beauty" of the "process of world making" she had seen at Niagara Falls. He remarked in a letter, She was very agreeable and managed to talk on a most wonderful number of subjects, considering the limited time. I was astonished to find how little ugly she is, but as it appears to me, she is overwhelmed with her own projects, her own thoughts and own abilities. Erasmus palliated all this, by maintaining one ought not to look at her as a woman.Significantly, Martineau's earlier popularization of Thomas Malthus' theories of population control may have helped convince Charles to read Malthus, which provided the breakthrough ideas for his nascent theory of evolution.