Evidence From Biogeography

BioMoz — Sat, 11 Apr 2009 06:25:40 +0000

Biogeography means the study of geographical distribution of species. The story of Darwin’s theory of natural selection begins in 1831, when he joined as an unpaid naturalist on a five year navigational mapping expedition of the British Admiralry aboard the ship H. M. S. Beagle. During this voyage, Darwin observed and studied a wide variety of plants and animals on continents and islands of volcanic origin, the Galapagos islands, which lie on the equator about 900 kilometer off the West Coast of South America. There, he found giant tortoises, meter-long marine and land iguanas, many unusual plants, insects, lizards and sea shells. These is called evidence from bio geography.
The Galapagos islands consisted of twenty-two different islands that were only a few miles apart. Darwin noticed that the Galapagos islands have many endemic (native, found nowhere else) species of plants and animals. He was amazed to record that in the islands insect-eating warblers and woodpeckers were absent. Instead, various types of inches, a group of small black birds, which were originally seed-eating but have assumed insect-eating pattern, were present in the islands. These finches are often referred to as Darwin’s finches. He also observed that different geographical localities have similar habitats but house different species. The finches of different islands varied yet they were closely related to each other.
Why the plants and animal species of the islands are closely related to species of the nearest mainland or neighboring island? Why the islands contain more different species of finches than the entire South American continent? Darwin realized that such questions could be explained on the ground that from ancestral group, living in a particular geographical area, descendant populations could radiate into other areas, where the new environmental conditions brought about the suitable adaptation by evolution. He reasoned that after originating from a common ancestral seed-eating stock the finches radiated to different geographical areas and underwent profound adaptive changes, especially in the patterns of beak. Living in isolation for long period of time new kinds of finches emerged that could function and survive in the new habitats. Such an evolutionary process, giving rise to new species adapted to new habitats and ways of life, is called adaptive radiation.
Furthermore, Australia is the home to the great diversity of pouched mammals but relatively few placental mammals. Darwin explained that adaptive radiation gave rise to a variety of marsupials in Australia in the same process of adaptive radiation as found in the finches in the Galapagos Islands.
Natural selection can lead to similar adaptation for survival in the similar habitats. This form of evolutionary changes is called convergent or parallel evolution. For example, some of the marsupials of Australia resemble equivalent placental mammals that live in similar habitats of other continents. Australia separated from other continents more than 50 million years ago. Most likely, marsupials arrived in Australia before its separation from Antarctica and evolved in isolation earlier than placental mammals. Natural selection has favored changes that made the two groups more alike. In other words, their phenotypes have converged.
Furthermore, Australia is the home to the great diversity of pouched mammals but relatively few placental mammals. Darwin explained that adaptive radiation gave rise to a variety of marsupials in Australia in the same process of adaptive radiation as found in the finches in the Galapagos islands.
Natural selection can lead to similar adaptation for survival in the similar habitats. This form of evolutionary changes is called convergent or parallel evolution. For example, some of the marsupials of Australia resemble equivalent placental mammals that live in similar habitats of other continents. Australia separated from other continents more than 50 million years ago. Most likely, marsupials arrived in Australia before its separation from Antarctica and evolved in isolation earlier than placental mammals. Natural selection has favored changes that made the two groups more alike. In other words, their phenotypes have converged.

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Evidence From Biogeography