He was considered the 19th century's leading expert on the geographical distribution of animal species and is sometimes called the "father of biogeography". Wallace was one of the leading evolutionary thinkers of the 19th century and made many other contributions to the development of evolutionary theory besides being co-discoverer of natural selection. These included the concept of warning colouration in animals, and the Wallace effect, a hypothesis on how natural selection could contribute to speciation by encouraging the development of barriers against hybridisation. Wallace's 1904 book Man's Place in the Universe was the first serious attempt by a biologist to evaluate the likelihood of life on other planets. He was also one of the first scientists to write a serious exploration of the subject of whether there was life on Mars.
Wallace was strongly attracted to unconventional ideas (such as evolution). His advocacy of spiritualism and his belief in a non-material origin for the higher mental faculties of humans strained his relationship with some members of the scientific establishment.
Aside from scientific work, he was a social activist who was critical of what he considered to be an unjust social and economic system (capitalism) in 19th-century Britain. His interest in natural history resulted in his being one of the first prominent scientists to raise concerns over the environmental impact of human activity. He was also a prolific author who wrote on both scientific and social issues; his account of his adventures and observations during his explorations in Singapore, Indonesia and Malaysia, The Malay Archipelago, was both popular and highly regarded. Since its publication in 1869 it has never been out of print.
Wallace had financial difficulties throughout much of his life. His Amazon and Far Eastern trips were supported by the sale of specimens he collected and, after he lost most of the considerable money he made from those sales in unsuccessful investments, he had to support himself mostly from the publications he produced. Unlike some of his contemporaries in the British scientific community, such as Darwin and Charles Lyell, he had no family wealth to fall back on, and he was unsuccessful in finding a long-term salaried position, receiving no regular income until he was awarded a small government pension, through Darwin's efforts, in 1881.
Alfred Wallace was born in the Welsh village of Llanbadoc, near Usk, Monmouthshire. He was the seventh of nine children of Thomas Vere Wallace and Mary Anne Greenell. Mary Anne was English; Thomas Wallace was probably of Scottish ancestry. His family, like many Wallaces, claimed a connection to William Wallace, a leader of Scottish forces during the Wars of Scottish Independence in the 13th century. Thomas Wallace graduated in law, but never practised law. He owned some income-generating property, but bad investments and failed business ventures resulted in a steady deterioration of the family's financial position. His mother was from a middle-class English family from Hertford, north of London. When Wallace was five years old, his family moved to Hertford. There he attended Hertford Grammar School until financial difficulties forced his family to withdraw him in 1836, when he was aged 14.