By Branden Holmes (Surroundx) on November 28, 2010

The mechanism by which new species arise is called speciation. There are three basic ways in which this may happen. Firstly, a previously reproductively-connected population may become geographically separated into two or more sub-populations because of a geographical barrier which arises. Interbreeding between these sub-populations then becomes physically impossible. And if they stay geographically isolated for a long enough period of time, different selection pressures combined with genetic drift will cause them to diverge genetically. This is called allopatric speciation and is believed to be the main way in which new species arise.

The second way in which new species may arise is called sympatric speciation. In contrast with allopatric speciation, there is no geographical isolation. Rather, the barrier which prevents them from interbreeding is reproductive or habitual. There may be a divergence amongst females as to which types of males they prefer to mate with. Or some members of a population may diverge from the rest in diet or the time of day (or night) that they are active. And the last way in which new species arise, and by far the rarest, is anagenesis. It literally means "straight-line" evolution to denote the fact that one species simply evolves into another over a long period of time. The conditions of life change so much that in constantly adapting to these changed conditions, the species ends up so far from its starting point that it has become a new species. Documented cases of anagenesis are very rare, but that probably reflects a lack of evidence rather than a lack of cases. It is very hard to prove that one species evolved into another one, especially when fossils of most species are either very rare or non-existent.

Related articles:
evolution, speciation

About Branden Holmes
I am an amateur evolutionist interested in the theoretical side of the subject.

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