speciation, theory of

(18TH CENTURY)

Also called geographic speciation, this theory is most often associated with Ernst Mayr (1904- ), an evolutionary biologist at Harvard University (although many other biologists have theorized on the subject).

It asserts that new species arise among sexually reproducing organisms because geographic isolation enables a small subgroup to diverge genetically from the larger, established population.

This isolated subgroup may diverge owing to particular environmental pressures, mutations or GENETIC DRIFT. For this subgroup to become a new species, its unique characteristics must allow it to survive in its isolated location, and its gene pool must be protected from mixing with that of other species.

Also see: ALLOPARAPATRIC SPECIATION, ALLOPATRIC SPECIATION, COHESION SPECIES CONCEPT, GENETIC REVOLUTION, PARAPATRIC SPECIATION, SALTATION SPECIATION, species essentialism, STASIPATRIC SPECIATION, SYMPATRIC SPECIATION

Source:
M Ereshefsky, The Units of Evolution: Essays on the Nature of Species (Cambridge, Mass., 1992)

Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within lineages.^[1][2][3] Charles Darwin was the first to describe the role of natural selection in speciation in his 1859 book On the Origin of Species.^[4] He also identified sexual selection as a likely mechanism, but found it problematic.

There are four geographic modes of speciation in nature, based on the extent to which speciating populations are isolated from one another: allopatric, peripatric, parapatric, and sympatric. Speciation may also be induced artificially, through animal husbandry, agriculture, or laboratory experiments. Whether genetic drift is a minor or major contributor to speciation is the subject matter of much ongoing discussion.

Rapid sympatric speciation can take place through polyploidy, such as by doubling of chromosome number; the result is progeny which are immediately reproductively isolated from the parent population. New species can also be created through hybridisation followed, if the hybrid is favoured by natural selection, by reproductive isolation.