Ways new species originate

Jun 30th, 2015
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University of Ottawa
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Two major modes of speciation are theoretically possible: geographic and nongeographic. In geographic speciation, initial isolation results from geographic separation of the populations.

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Speciationistheprocess whereby new species are formed. The following events are thought to occur in most cases. In the first step, extrinsic isolation, an existing species becomes subdivided by some extrinsic event, such as a climatic change, the formation of a physical barrier (such as a mountain range), or its invasion of a new habitat or island. Subdivision may also occur merely because many hundreds of generations may be required for individuals to disperse from one end of the species' geographic range to another. In the second step, differentiation, the isolated populations diverge genetically, which they can do more rapidly than populations exchanging individuals with other populations. Populations may diverge either at random or as a result of natural selection. In the third step, intrinsic isolation, some form of isolation evolves among the populations; this is dependent on the organisms rather than the environment. Such isolation may result from preferences during courtship or from genetic incompatibility, in which offspring of matings between the differentiated populations are no longer viable or fertile; the mule is an example. In the final step, independence, the newly separated populations continue to evolve independently and may subsequently invade each other's geographic ranges without hybridization. Each of these steps has been demonstrated in the field and laboratory with various organisms.Twomajormodesofspeciation are theoretically possible

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