Species and Speciation: Overview


The species is the fundamental or basic unit of organic or biological diversity, usually characterised as a group of individuals or populations of individuals with interbreeding or genealogical relationships. Understanding the nature of species can be challenging when considering sexual versus asexual organisms. Identifying species is also challenging, for example, when studying the fossil record, or when speciation is not yet complete. Speciation is the process leading to the formation or origin of species. As such, speciation is the process by which reproductive and/or genealogical boundaries form around groups of organisms. Commonly understood forces of evolution causing divergence in phenotypes contribute to the formation of species. Geographic, ecological, behavioural and genetic factors are also important to understanding how the process works.

Key Concepts:

  • Species are fundamental units of biodiversity but can be defined in different ways, from either a prospective (future) or retrospective (historical) perspective.

  • Speciation is the study of how new species form and may be brought about by a multitude of phenotypic changes.

  • The causes of speciation are complex and likely include a diversity of evolutionary forces such as natural selection, sexual selection and genetic drift that lead to divergence in phenotype.

  • Divergence in specific phenotypes is important to speciation if they directly or indirectly cause a reduction in gene flow between newly forming species.

  • The genetics of speciation is the study of the genetic basis of phenotypic evolution that leads to a reduction in gene flow between newly forming species.

Keywords: allopatric; barriers to gene exchange; diversity; homoploid speciaton; polyploid speciation; sexual selection; sympatric

Figure 1.

Different categories of barriers to gene exchange.



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Further Reading

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Grant P and Grant R (2008) How and Why Species Multiply. Princeton: Princeton University Press.

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Stebbins GL (1950) Variation and Evolution in Plants. New York: Columbia University Press.

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Shaw, Kerry L(Aug 2012) Species and Speciation: Overview. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001742.pub2]