The study at the geographic distribution of plants and animals is called biogeography. Biogeographers explain the reason of distribution of organisms in different regions. Biogeographic studies show that life in different parts of the world has distinctive evolutionary histories. Biogeographers explain following, . factors:
- Geographical ‘barriers: They explain how similar groups of organisms can
live in different places’. These places, are separated by impenetrable barriers. For example, native cats live in most continents of the earth. But they cannot cross open oceans. They have common ancestry. But they have undergone millions of years of independent evolution. Therefore, they have developed differences.
- Evolutionary adaptations in the isolated organisms: Biogeographers also • explain that the plants and animals are separated by geographical barriers. They were very different in spite of similar environments. For example, the animals that inhabit Australia and Tasmania are very different from animals in any other part of the world. The major native herbivores of Australia and Tasmania are kangaroos (Macropus).’ Members of the deer and cattle perform the same role in the other parts of the world. Similarly. the Tasmanian wolf (tiger) (Thylacinus cynocephalus) is extinct now. It was a predatory marsupial.
- Life on islands: The biogeographers explain the presence of only few and ‘2-ittue resident species in oceanic islands. They write island colonization and equent evolutionary events. These evolutionary events are different from the ancestral mainland
during his observation in groups. Charles Darwin explained this distribution Galapagos
Fig: Geographical regions
Bi geographical regions
Modern evolutionary biologists recognize the importance of geological event. These events are volcanic activity, movement of great landmasses. climatic • changes, and geological uplift. They create or remove barriers to the movements • of plants and animals. Biogeographers divide the world into six major biogeographic regions. These regions are:
1. Ethiopian regions: It includes most of African continent. It is separated from he Palearctic region by Arabian Desert Sahara.
2. Palearctic region: It includes most of the Europe, China, and Russia. It is eparated from the Oriental regions by Himalayan Mountains.
3. Oriental regions: It includes sub Himalayan region, Pakistan, India etc.
4. Australian region: It is composed of continent of Australia. It is separated from the Oriental region by deep ocean channel.
5. Neacrtic region: It is composed of USA, Canada etc. It is separated from the en+,‘ tdi eyk,:” by mountains of Southern Mexico. .
6. Neotropical region: It is composed of most of the South America.
Th study of fossil is called paleontology. Fossil provide direct evidence of evo ution. Fossils are evidence ,of plants and animals that existed in the past. The .e plants and animal’s’ incorporated into the earth’s, crust. ‘Sediments quickly cov • them It prevents scavenging and reduces the supply of oxygen Thus decomposition occurs slowly. Fossilization is mostly occurs in aquatic or semi aquatic environments. Thus the fossil record is more complete for those groups of organisms living in or around water. Some gaps may be present ih the fossil record. But paleontology produces nearly complete understanding of many evolutionary lineages. Paleontologists estimate that the earth is about 4.6 billion years old. They have also used the fossil record to describe the history of life on the earth.
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Fig: Evolutionary stages of horse