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| Geological Distribution |
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| The organisms show particular patterns of distribution on earth. The distribution of the species give an indication of how the earth was earlier. It is believed that the earth was a single mass called the Pangea. It consisted of two large continental masses called Laurasia and Gondwanaland that were interconnected by land bridges. These land masses have continuously drifted away from each other. This theory was proposed by Alfred Wegener and called the theory of continental drift. A proof of this comes from the distribution of lungfish. As can be seen in the maps below, the regions where the lungfish is presently distributed were all close together in the early days. |
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| An interesting case is of Galapagos Islands that are situated off the coast of Africa in the Pacific Ocean. It was in these islands that Darwin noticed that there were differences between the species of the island and mainland. This led him to think about the mechanism of evolution. He noticed that the species were of more varieties on the island. The large-sized varieties of the species were also found there. For example, he found the giant tortoise attained a huge size of 2m length and 260kg weight. The iguana lizards were also larger and more abundant than the land species. There were 13 species of finches as opposed to only one on the mainland. |
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| All these examples pointed to the fact that the factors limiting the size and types of organisms were food, space and mate. The islands had less competition and plentiful vegetation. This resulted in large sized species on the land. The species developed more varieties and this resulted in natural selection of varieties that were suited best to the environment. |
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