Speciation

Speciation is one suggested process by which new species are thought to arise, possibly by Darwin-Wallace evolution. It occurs due to natural selection and separation of populations of the same species, allowing allele frequencies in the two groups to change independently. See evolution for a detailed dissection of the many problems of this theory.

Species

A species is:

"a group of organisms, with similar morphological, physiological, biochemical and behavioural features, which can interbreed to produce fertile offspring, and are reproductively isolated from other species." - Jones M. & Gregory J., Biology 2, 2001, Cambridge University Press, ISBN 0-521-79714-4

morphological features

structural features, such as anatomy

physiological features

how the body functions

biochemical features

sequence of bases in DNA

sequence of amino acids in proteins

For example, all donkeys look alike, have similar physiology and biochemistry and the same genome. Donkeys can successfully interbreed with other donkeys to produce more fertile donkeys. Donkeys can interbreed with a similar species; horses. However, the offspring (called mules) are infertile and cannot reproduce with each other. Therefore donkeys and horses are separate species.

Unfortunately the interbreeding test is often difficult to carry out, especially if the organisms being investigated are rare, take a long time to reproduce or do not breed in captivity.