- Wallace effect
The Wallace Effect is the hypothesis that natural selection can contribute to the
reproductive isolation of incipient species by encouraging varieties to develop barriers to hybridization.Historical development
In 1889,
A. R. Wallace wrote the book "Darwinism", which explained and defendednatural selection . In it he proposed that natural selection could cause thereproductive isolation of two varieties by encouraging the development of barriers againsthybridization , and thus contribute to the development of new species. He suggested the following scenario. When two varieties of a species had diverged beyond a certain point, each adapted to particular conditions, hybrid offspring would be less well adapted than either parent form. At that point natural selection will tend to eliminate the hybrids. Under such conditions natural selection would also favor the development of barriers to hybridization, since individuals that avoided hybrid matings would tend to have more fit offspring. This would contribute to the reproductive isolation of the two incipient species. [ Slotten The Heretic in Darwin's Court pp. 413–415 ]Current status
It is sometimes also called "reinforcement" and it continues to be a topic of research in evolutionary biology today as it is potentially an important factor in
speciation , especiallysympatric speciation . Its validity has been supported by mathematical models, and recently by empirical field data on the evolution of differing flowering times as a reproductive isolation mechanism [cite web|last=Ollerton|first=J|title=Flowering time and the Wallace Effect|url=http://oldweb.northampton.ac.uk/aps/env/lbrg/journals/papers/OllertonHeredityCommentary2005.pdf|publisher=Heredity, August 2005|accessdate=2007-05-22] , as well as sex-chromosome linked species preference in flycatchers [cite journal | last=Sæther | first=Stein A. | last2=Sætre | first2=Glenn-Peter | last3=Borge | first3=Thomas | last4='et al' | title=Sex-chromosome linked species recognition and evolution of reproductive isolation in flycatchers | journal=Science | issue=318 | pages=95–97 |date=2007 | url=http://www.sciencemag.org/cgi/content/full/318/5847/95 | doi=10.1126/science.1141506 | volume=318 | pmid=17916732]Notes
References
* Slotten, Ross A. (2004) "The heretic in Darwin's court: the life of Alfred Russel Wallace" Columbia University Press: New York. ISBN 0-231-13010-4
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