[[Image:Darwin's finches.jpeg|thumb|Four of the [[Darwin's finches|13 finch species]] found on the [[Galápagos Islands|Galápagos Archipelago]], and thought to have evolved by an adaptive radiation that diversified their [[beak]] shapes to adapt them to different food sources.]]

'''Adaptive radiation''' describes the rapid [[speciation]] of a single or a few [[species]] to fill many [[ecological niche]]s. This is an [[evolution]]ary process driven by [[natural selection]], successful and novel adaptation, and sometimes by [[mutation]] (heritable/genetic variation).

==Causes of adaptive radiation==



===Opportunity===

Isolated [[ecosystem]]s, such as [[archipelago]]s, [[mountain]] areas, and newly formed lakes can be colonized by a species which, upon establishing itself, undergoes rapid [[divergent evolution]].
[[Monotremes]], [[marsupials]], and [[cichlids]] are examples of geographic isolation. Monotremes evolved before the evolution of placental mammals, and they are found today only in [[Australia]], a 'continent country'. Marsupials, which also evolved before the appearance of placental mammals are also common in Australia. In Australia, marsupials evolved to fill many ecological niches that placental mammals fill on other [[continents]]. In [[Lake Victoria]] in [[Africa]], it is thought that more than 300 species of cichlids adaptively radiated from one parent species in only 15,000 years.

[[Richard Leakey]] (see below) wrote, "Biologists who have studied the fossil record know that when a new species evolves with a novel adaptation, there is often a burgeoning of descendent species over the next few million years expressing various themes on that initial adaptation - a burgeoning known as '''adaptive radiation'''. The Cambridge University anthropologist [[Robert Foley]] has calculated that if the evolutionary history of the bipedal apes followed the usual pattern of adaptive radiation, at least sixteen species should have existed between the group's origin 7 million years ago and today."

===Extinction===

Adaptive radiation can also occur after [[mass extinctions]]. The best example of this is after the [[Permian-Triassic extinction event]], where [[biodiversity]] increased massively in the [[Triassic]]. The end of the [[Ediacaran]] and the beginnings of [[multicellular organisms|multicellular life]] lead to adaptive radiations and the genesis of new phyla in the [[Cambrian]] period.

==Adaptive radiation in popular culture==

In [[science fiction]] sometimes adaptive radiation of [[human]]s is imagined. This often makes for interesting multi-species [[science fiction universe|worlds]].

==References==

*Wilson, E. et al. ''Life on Earth,'' by Wilson,E.; Eisner,T.; Briggs,W.; Dickerson,R.; Metzenberg,R.; O'brien,R.; Susman,M.; Boggs,W.; (Sinauer Associates, Inc., Publishers, Stamford, Connecticut), c 1974. Chapters: ''The Multiplication of Species; Biogeography,'' pp 824-877. 40 Graphs, w species pictures, also Tables, Photos, etc. Includes [[Galápagos Islands]], [[Hawaii]], and [[Australia (continent)|Australia]] subcontinent, (plus [[St. Helena]] Island, etc.).

*Leakey,Richard. ''The Origin of Humankind'' - on adaptive radiation in biology and human evolution, pp. 28-32, 1994, Orion Publishing.

[[Category:Speciation]]
[[Category:Evolution]]

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