Facts Of Evolution (Part 4): Speciation And Extinction.
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1. Does The Evidence Support Evolution?
2. Vitamin C And Common Ancestry
3. Are We Descended From Viruses?
4. Does The Fossil Record Support Evolution?
5. Where Are The Transitional Forms?
SPECIATION is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages.
Whether genetic drift is a minor or major contributor to speciation is the subject of much ongoing discussion. There are four geographic modes of speciation in nature, based on the extent to which speciating populations are geographically isolated from one another: allopatric, peripatric, parapatric, and sympatric. Speciation may also be induced artificially, through animal husbandry or laboratory experiments. Observed examples of each kind of speciation are provided throughout.
In biology and ecology, EXTINCTION is the end of an organism or group of taxa. The moment of extinction is generally considered to be the death of the last individual of that species (although the capacity to breed and recover may have been lost before this point). Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa, where a species presumed extinct abruptly "re-appears" (typically in the fossil record) after a period of apparent absence.
Through evolution, new species arise through the process of speciation—where new varieties of organisms arise and thrive when they are able to find and exploit an ecological niche—and species become extinct when they are no longer able to survive in changing conditions or against superior competition.
A typical species becomes extinct within ten million years of its first appearance, although some species, called living fossils, survive virtually unchanged for hundreds of millions of years. Extinction, though, is usually a natural phenomenon; it is estimated that 99.9% of all species that have ever lived are now extinct.
Mass extinctions are relatively rare events, however, isolated extinctions are quite common. Several extinctions during the Holocene extinction have been attributed to the rise of human activity; however, there is no clear consensus among the scientific community on the effect of human activity on extinctions. Only recently have extinctions been recorded and scientists have become alarmed at the high rates of recent extinctions. It is estimated most species that go extinct have never been documented by scientists. Some scientists estimate that up to half of presently existing species may become extinct by 2100.
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