The factors that influence evolution are (1) variation within species. (2) Overpopulation = the struggle for existence. (3) Inheriting favoured characteristics = natural selection. (4) A process that leads to new species. Charles Darwin (1809-1882) knew about these but was unable to reveal variation's rationale in simple terms until he read the work of Henry Waiter Bates (1825-1892). Bates is an enigma, a Victorian travelling naturalist overshadowed by his more famous contemporaries like Darwin and Alfred Russel Wallace (1823-1912). This thesis attempts to unravel this enigma, and examines the life of Bates in the intellectual setting of the origin of species. Henry Walter Bates, the eldest child of a Leicestershire hosier, was self-educated in the natural sciences. He grew up in a radical artisan home of the type that played such an important a part in the development of early Victorian middle class culture. From the start, he found natural history appealing. As a young man, Bates set out 'With Wallace to earn a living as a specimen collector. Bates and Wallace also shared an enthusiasm to examine the origins of life. With only limited financial support, they more or less single-handedly opened up the Amazon region to the Victorian naturalist and were probably, by default, the first professional naturalists.