Alfred Russel Wallace (1823–1913) is famous for presenting a theory of evolution with Charles Darwin at the Linnean Society in London in 1858.
This paper traces how Wallace was led from biological distribution to the idea of the theory of evolution, and what the concept of an area of biological distribution and its boundary lines mean within the methodology of geography.
Information about various creatures and their distribution was collected from all over the world during the 18th and 19th centuries. It became clear that species differed in different regions, even those having similar environmental conditions. This was in contradiction to the theory of creationism, in which each species was created to suit its environment.
Wallace, in expeditions to the Amazon, reported finding closely related, yet different, species on opposite sides of a geographical barrier, such as the opposing banks of a wide river.
Wallace thought that groups of what were originally the same species evolved apart from one another over time after becoming isolated from each other. Upon further development of this idea, while in Sarawak, Borneo in 1855, Wallace wrote a thesis and presented the theory that “every species has come into existence coincident both in space and time with a pre-existing closely allied species.” In other words, he insisted that speciation is not sudden divergence but continuous spatial and temporal evolution.
Wallace’s biogeography integrated geological data and climate data, such as glacial action or sea-level changes based on the permanence of the arrangement of continents and oceans, and comprehensively treated the concepts of migration habits and dispersal, evolutionary adaptation, and the divergence of life as the principles of research. In this way, Wallace’s theory of evolution places more importance on the influence of environment or the geographic distribution of life than Darwin did.
At a macroscopic level, Wallace set out six zoogeographic regions in the world, based on the permanence of the global arrangement of oceans and continents. However, in explaining those boundaries or marginal regions such as islands, the influence of upheavals and subsidence of land masses, the actions of glaciers, and sea-level changes, etc. continued to be of importance.
Also, the Wallace Line discovered by Wallace in the Malay Archipelago is not only a faunal boundary between the Oriental region and Australian region, but it has been seen today as a subduction zone in plate tectonics theory, where the Australian continental crust collides and sinks beneath the Eurasian continental crust.