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Origin of Species

        In 1835, when Darwin first landed on the Galapagos Islands, he discovered new species. Species is a Latin word that means "kind" or "appearance," and the Biological Species Concept defines a species as a population whose individuals are able to interbreed and produce fertile offspring. Scientists study different species of organisms to classify them and place them into groups.
For example, these spiders may all look different however since they are able to interbreed, they are considered the same species.

        The origin of new species, or speciation, is part of the Evolutionary Theory, since biological diversity depends on the appearance of new species. However, new species do not randomly appear; one way in which they originate is from something called Natural Selection. Natural Selection is essentially when random genetic mutations that are favorable occur from one generation of a population to the next. This means that the new organism has some kind of advantage over its parents or its parent population. Over (usually) many years and many generations, the newer generations eventually diversify from the previous generations enough so that the populations can no longer interbreed, whether this is a result of anatomical or environmental change. This process, where one common ancestor branches off to become many new species, is called Sympatric Speciation. The chart below illustrates how Natural Selection works; one species may mutate into different organisms, who eventually evolve into completely new species.
        However, Natural Selection is not the only cause of the appearance of new species; reproductive isolation also causes new species to appear. It has already been established that when two organisms cannot interbreed, they are considered different species. While this applies in a morphological sense (organisms who cannot physically mate are different species), it also applies in a geographical sense. This means that when two organisms cannot mate due to land barriers such as a large mountain or river that cannot be crossed, those organisms are considered different species. Although they may physiologically be able to mate, the fact that the two organisms cannot reach each other in order to mate makes them two different species. This process, where one species is separated into two or more separate populations by a geological barrier, is called Allopatric Speciation.