In 1874, when Darwin was preparing the second edition of Descent of Man, he received letters from all over the world in reply to his queries about human behaviour; one in particular would have stirred up unexpected memories of his own time among the native peoples of South America.  Titus Munson Coan, an American doctor, passed on a message to Darwin from his father, also called Titus Coan, who, as a young missionary, had spent a few hazardous weeks among the indigenous peoples of Patagonia on the north shore of the Magellan Strait. Darwin’s queries about the practice of infanticide reached Coan in Hawaii where he and his wife had been running a mission station since 1835.  Through his son, he told Darwin that although infanticide was sometimes practised, it was not prevalent in Hawaii, and moreover didn’t favour the survival of one sex over the other as Darwin had suspected it might.

James Crichton-Browne became one of the most distinguished psychiatrists of the late nineteenth-century, but the letters he exchanged with Charles Darwin as the young and overworked superintendent of the largest mental asylum in England, are almost the only personal papers to survive from this stage of his career.  They are an extraordinary glimpse not only into Crichton-Browne's research and the development of Darwin's thinking, but into the everyday lives of the patients whose records Crichton-Browne sent on.

Known to his family as ‘Frank’, Charles Darwin’s seventh child himself became a distinguished scientist. He was an undergraduate at Trinity College, Cambridge, initially studying mathematics, but then transferring to natural sciences.