In 1858, aged thirty-five, weak with malaria, isolated in the remote Spice Islands, Alfred Russel Wallace wrote to Charles Darwin: he had, he said excitedly, worked out a theory of natural selection. Darwin was aghast - his work of decades was about to be scooped. Within a fortnight, his outline and Wallace's paper were presented jointly in London. A year later, with Wallace still at the opposite side of the world, "On the Origin of Species" was published. Wallace had none of Darwin's advantages or connections. Born in Usk, Gwent, in 1823, he left school at fourteen and in his mid-twenties spent four years in the Amazon collecting for museums and wealthy patrons, only to lose all his finds in a shipboard fire in mid-Atlantic. He vowed never to travel again. Yet two years later he was off to the East Indies, beginning an eight-year trek over thousands of miles; here he discovered countless unknown species and identified for the first time the point of divide between Asian and Australian fauna, 'Wallace's Line'. With vigour and sensitivity, Peter Raby reveals Wallace as a courageous and unconventional explorer. After his return, he plunged into a variety of controversies, staying vital and alert until his death at the age of 90, in 1913. Gentle, self-effacing, and remarkably free from the racism that blighted so many of his contemporaries, Wallace is one of the neglected giants of the history of science and ideas. This stirring biography - the first for many years - puts him at centre stage, where he belongs.