He married Elizabeth Fraser in July of 1882. Later he married Charlotte Mildred Massingberd (1868–1940), but had no children from either marriage.
He was Chairman of the British Eugenics Society between 1911-1928, (succeeding his cousin once removed Francis Galton), and became Honorary President from 1928 until his death. He was an officer of the Royal Geographical Society from 1908 to 1911, and then its president
He corresponded with and mentored the geneticist and statistician Ronald Fisher, their correspondence can be found here (http://www.library.adelaide.edu.au/digitised/fisher/natsel/index.html). Fisher's 1930 book The Genetical Theory of Natural Selection is dedicated to him.
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