Alfred Russel Wallace (1823-1913) was a Welsh naturalist, explorer, geographer, anthropologist and biologist. He is best known for independently proposing a theory of evolution due to natural selection that prompted Charles Darwin to publish his own theory. He was considered the 19th century's leading expert on the geographical distribution of animal species and is sometimes called the "father of biogeography". One of the the first prominent scientists to raise concerns over the environmental impact of human activity. Wallace was one of the leading evolutionary thinkers of the 19th century and made a number of other contributions to the development of evolutionary theory besides being co-discoverer of natural selection. Wallace was strongly attracted to unconventional ideas and advocated Spiritualism. He was a prolific author who wrote on both scientific and social issues. He died in 1913 at the age of 90.