Alfred Russel Wallace was one of the greatest naturalists of all time, second in that regard perhaps only to Charles Darwin. Wallace's early training was as a surveyor and architect, but after 1845 he devoted his long and productive career to the study of natural history. He undertook several famous expeditions to the tropics, where he collected many species of plants and animals previously unknown to science. His most memorable expeditions were to the Amazon and Negro Rivers of South America (1848-1852), and to the East Indies (1854-1862), visiting peninsular Malaysia, Borneo, Java, Sumatra, various other islands of Indonesia, New Guinea, and Australia.

While in Southeast Asia, Wallace developed an outline of a theory of evolution by natural selection, which he shared with Charles Darwin in a letter in 1858. Wallace's idea astonished Darwin, who had been working on a similar theory for more than a decade, based on his...