Geographic isolation, or
allopatry, is a term used in the study of
evolutionIn biology, evolution is change in the genetic material of a population of organisms from one generation to the next. Though changes produced in any one generation are normally small, differences accumulate with each generation and can, over time, cause substantial changes in the population, a...
. When part of a population of the
same speciesIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
becomes geographically isolated from the remainder, it may over time evolve characteristics different from the parent population (due to genetics/genetic) change following geographical isolation, then if the geographical barriers are removed (perhaps due to human activity), members of the two populations will be unable to successfully mate with each other.
Geographic isolation, or
allopatry, is a term used in the study of
evolutionIn biology, evolution is change in the genetic material of a population of organisms from one generation to the next. Though changes produced in any one generation are normally small, differences accumulate with each generation and can, over time, cause substantial changes in the population, a...
. When part of a population of the
same speciesIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
becomes geographically isolated from the remainder, it may over time evolve characteristics different from the parent population (due to genetics/genetic) change following geographical isolation, then if the geographical barriers are removed (perhaps due to human activity), members of the two populations will be unable to successfully mate with each other. At this point, a new species has emerged. Geographical isolation is thus a key factor in
speciationSpeciation 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...
, the formation of new species - also termed
allopatric speciationAllopatric and allopatry are terms from biogeography, referring to organisms whose ranges are entirely separate, so that they do not occur in any one place together. If these organisms are closely related Allopatric and allopatry are terms from biogeography, referring to organisms whose ranges are...
. The animals would mate and eventually become hybrid species.
However, it is more common for natural selection. This is particularly likely to happen if the isolated population is small, because of
founder effectIn population genetics, the founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. It was first fully outlined by Ernst Mayr in 1952, using existing theoretical work by those such as Sewall...
s, or if the population become isolated in an environment which makes new demands upon it. Much research has shown that this is a major reason why there are so many different species throughout the world.
If there is sufficient gene there to be considerable
geneticGenetics, , a discipline of biology, is the science of heredity and variation in living organisms. The fact that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding...
and
phenotypicA phenotype is any observable characteristic or trait of an organism: such as its morphology, development, biochemical or physiological properties, or behavior. Phenotypes result from the expression of an organism's genes as well as the influence of environmental factors and possible interactions...
change without the loss of the capacity for interbreeding - interbreeding is simply prevented by the geographical separation of populations. In this case the populations are normally regarded as
subspeciesSubspecies in biological classification, is 1) a taxonomic rank subordinate to species, or 2) a taxonomic unit, a taxon in that rank...
.
The African Elephant for instance has always been regarded as a single species. Because of morphological and
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
differences some scientists classify the elephants into three
subspeciesSubspecies in biological classification, is 1) a taxonomic rank subordinate to species, or 2) a taxonomic unit, a taxon in that rank...
. Researchers at the
University of California, San DiegoThe University of California, San Diego is a public research university located in La Jolla, San Diego, California, United States...
(UCSD) have argued that divergence due to geographical isolation has gone further, and the elephants of
West AfricaWest Africa or Western Africa is the westernmost region of the African continent. Geopolitically, the UN definition of Western Africa includes the following 16 countries distributed over an area of approximately 5 million square km:*Benin...
should be regarded as a separate species from either the
savannaA savanna, or savannah, is a grassland ecosystem characterized by the trees being sufficiently small or widely spaced so that the canopy does not close...
elephants of Central, Eastern and Southern Africa, or the forest elephants of Central Africa.
Other cases arise where two populations that are quite distinct morphologically, and are native to different
continentA continent is one of several large landmasses on Earth. They are generally identified by convention rather than any strict criterion, with seven regions commonly regarded as continents – they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...
s, have been classified as different species; but when members of one species are introduced into the other's range, they are found to interbreed freely, showing that they were in fact only geographically isolated subspecies. This was found to be the case, for example, when the
MallardThe Mallard , probably the best-known and most recognizable of all ducks, is a dabbling duck which breeds throughout the temperate and sub-tropical areas of North America, Europe, Asia, Africa, New Zealand , and Australia...
Anis platyrhynchos was introduced into
New ZealandNew Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses , and numerous smaller islands, most notably Stewart Island/Rakiura and the Chatham Islands. The indigenous Māori named New Zealand Aotearoa, commonly translated as The Land of the Long White Cloud...
; it interbred freely with the native Grey Duck, which had been classified as a separate species,
Anas superciliosa; it is controversial whether its specific status can now be retained.