Wallace and the Wallace line

Alfred Russel Wallace, OM, FRS (8 January 1823 – 7 November 1913) was a British 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.

Wallace did extensive fieldwork, first in the Amazon River basin and then in the Malay Archipelago, where he identified the Wallace Line that divides the Indonesian archipelago into two distinct parts, one in which animals closely related to those of Australia are common, and one in which the species are largely of Asian origin. He was considered the 19th century's leading expert on the geographical distribution of animal species and is sometimes called the "father of biogeography".^[1] 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. 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 hybridization.Wallace was strongly attracted to unconventional ideas. His advocacy of Spiritualism and his belief in a non-material origin for the higher mental faculties of humans strained his relationship with the scientific establishment, especially with other early proponents of evolution. In addition to his scientific work, he was a social activist who was critical of what he considered to be an unjust social and economic system in 19th-century Britain. His interest in biogeography resulted in his being one of the first prominent scientists to raise concerns over the environmental impact of human activity. Wallace was a prolific author who wrote on both scientific and social issues; his account of his adventures and observations during his explorations in Indonesia and Malaysia, The Malay Archipelago, was one of the most popular and influential journals of scientific exploration published during the 19th century.

Wallce Line

Wallace's line delineates Australian and Southeast Asian fauna. The probable extent of land at the time of the last glacial maximum, when the sea level was more than 110 m lower than today, is shown in grey. Note the deep water of the Lombok Strait between the islands of Bali and Lombok formed a water barrier even when lower sea levels linked the now-separated islands and landmasses on either side.

The Wallace Line (or Wallace's Line) is a boundary that separates the ecozones of Asia and Wallacea (which is a transitional zone between Asia and Australia). West of the line are found organisms related to Asiatic species; to the east, a mixture of species of Asian and Australian origin are present. The line is named after Alfred Russel Wallace, who noticed this clear dividing line during his travels through the East Indies in the 19th century. The line runs through Indonesia, between Borneo and Sulawesi (Celebes); and through the Lombok Strait between Bali (in the west) and Lombok (in the east). Antonio Pigafetta had also recorded the biological contrasts between the Philippines and the Maluku Islands (Spice Islands) (situated on opposite sides of the line) in 1521 during the continuation of the voyage of Ferdinand Magellan (after Magellan himself had been killed on Mactan).

The distance between Bali and Lombok is small, a matter of only about 35 kilometers. The distributions of many bird species observe the line, since many birds do not cross even the smallest stretches of open ocean water. Some bats have distributions that cross the Wallace Line, but other mammals are generally limited to one side or the other; an example of an exception is the Crab-eating Macaque. Other groups of plants and animals show differing patterns, but the overall pattern is striking and reasonably consistent.