Alfred Russel Wallace (1823-1913) is one of the most famous 19thcenturynaturalists. He shared his research with Charles Darwin andindependently formulated the theory of natural selection. His mostextensive fieldwork was carried out in the Amazon River Basin and inthe Malay Archipelago, where his observations led him to propose animaginary line running between the region's islands. Today, this line isstill known as "Wallace's Line" and is the boundary between theorganisms of the Australian and Asian regions. In later years, Wallacebecame more of a social activist.