The continental drift theory and it's effects on evolution.

Essay by WendyUK April 2003

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Continental Drift is the principle that the continent landmasses have not remained in fixed positions, but have moved around the earth's surface apparently independently. It is important in evolution because of the effects it has had on evolution and taxonomic diversity, brought about by the collision and moving apart of landmasses. The drifting apart of land masses brings about vicariance, where organisms are split up by the development of barriers, isolating descendent populations which then evolve to form new taxa.

Pre-continental drift theory, it was believed that species originated in a particular area, and spread out from there to colonise new habitats. However, it was noted that on a worldwide scale many taxa had obvious close relatives in regions that were geographically widely separated with natural barriers i.e.; oceans, deserts or mountain chains. Therefore, continental drift theory was able to explain many previously unanswered questions. An example of this is Nothofagus.

Nothofagus is restricted to the southern hemisphere, and is widely dispersed geographically. Although there are significant morphological differences between the species of Nothofagus, they all have seeds seemingly poorly adapted for long range dispersal, and are also intolerant of immersion in salt water. Continental drift reconstruction recognises that the southern continents were once united as a single massive continental land mass called Gondwanaland, and this lends weight to the vicariance hypothesis. Further evidence comes from fossil record, where remains of pollen grains of Northofagus have been found in regions outside the present range of any living species, namely Antarctica, Western Australia and Patagonia. This also confirms that the climate of Antarctica in Cretaceous times was very different from today. Landmasses undergo major changes of climate as they move across different latitudes. This affects evolutionary processes in that greater species diversity accumulates under tropical climatic conditions. Another effect that continental...