Born in Aberdeen, he attended Gordon's College there before studying medicine at Marishal College. From 1889 till 1892 he practiced as a medical officer for a mining company in Thailand where he collected botanical specimens, but became more interested in the comparative anatomy of the primates and their evolution. After briefly working in Aberdeen again, he moved in 1895 to London where he taught anatomy at the London Hospital Medical School.
In 1908 he became Conservator of the Royal College of Surgeons, a position which he held until retirement in 1933. There he worked on human evolution and on the development of modern races, arguing that Homo sapiens had evolved much earlier than was then supposed. He became involved in the controversy surrounding the discovery of Piltdown Man in 1912 and tended to support its authenticity. During the Great War he was concerned with surgical problems relating to war injuries. He was President of the British Association in 1927, one outcome of which was the effort to preserve Charles Darwin's house at Down.