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Cladogenesis

Cladogenesis defines those cases of evolution in which one species develops into two or more through adaptation. The classic example is the different species unique to the Galapagos Islands, where small populations of creatures from South America evolved in response to their new ecosystem. Sometimes cladogenesis occurs rapidly in less-isolated populations when there has been a radical change in the environment of the creature. Cladogenesis is also called adaptive radiation.

An isolated population branches off from its ancestral species when it has accumulated a number of significant, independent variations that differentiate it from the original species. There is disagreement about what constitutes a new species, but it's generally agreed that if the mating of individuals from different populations cannot result in fertile and viable offspring, then they belong to different species.

Cladogenesis explains the development of a large assortment of species from a smaller set of ancestral species through evolution. Unlike anagenesis, speciation through cladogenesis does not require the extinction of the ancestral population. Through successive cladogenetic splits, either with or without the extinction of the ancestral population, the total number of species increases over time. Cladogenesis is probably a more common form of evolution and speciation than anagenesis.

Web Resources On Cladogenesis

The De-riving Force of Cladogenesis
Wikipedia: Cladogenesis

Book Resources On Cladogenesis

Species Diversity in Space and Time by Michael L. Rosenzweig
Evolution by Douglas J. Futuyma

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