Alfred Russel Wallace OM, FRS (1823 -1913) was a British naturalist, explorer, geographer, anthropologist and biologist. He did extensive fieldwork first in the Amazon River basin, and then in the Malay Archipelago. He is best known for independently proposing a theory of natural selection which prompted Charles Darwin to publish his own more developed theory sooner than intended. Wallace was considered the 19th century's leading expert on the geographical distribution of animal species and is sometimes called the "father of biogeography". He advocated spiritualism and believed in a non-material origin for the higher mental faculties of humans. He was also a social activist and was thus critical of what he considered to be an unjust social and economic system in 19th century Britain. His The Malay Archipelago became one of the most popular journals of scientific exploration of the 19th century. His other substantial works include Darwinism, (1889)and Is Mars Habitable? (1907).