Origin and Evolution of Life: Role of Reproductive Isolation and Speciation

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Role of Reproductive Isolation

Reproductive isolation is essential for a species to maintain its distinct identity and contribution to the formation of new species making organic evolution possible. Reproductive barriers prevent the two species from exchanging genes through reproduction. Reproductive isolation is the conditions as geographical barriers, that prevent potentially interbreeding populations from cross-fertilization and genetically distinct from each other. Reproductive isolation operates in the following ways:

Image of types of isolating mechanism.

Image of Types of Isolating Mechanism.

Image of types of isolating mechanism.


  • The evolution or formation of new species is termed as speciation. Speciation occurs in the following ways.

  • Allopatric speciation: When a large population of a species is geographically isolated into two or more groups and each group accumulates genetic variations in its gene pool and natural selection operates separately on each group’s gene pool.

  • Sympatric speciation: When a few individuals of a species within the same geographical area are became reproductively isolated from the main population, it forms a new species is called sympatric species and its origin is called sympatric speciation. Polyploidy and hybridization are two main methods of introducing sudden reproductive isolation responsible for origin of sympatric species.

Models of Speciation

There are two accepted models of speciation that give rise to the biodiversity.

  • Phyletic Gradualism model: In phyletic gradualism model, slow, steady change in species occurs over time. In this model, evolution processed continuously over long periods. Gradualism is rarely observed in the fossil record because the record is incomplete. Darwin also believed that evolution is a slow and gradual process.

  • Punctuated equilibrium: A new species arises through major changes in the beginning and then remain constant for long periods before changing again. This model was suggested by Niles Eldredge and Stephen Jay Gould (paleontologists).

image of Models of speciation (a) Phyletic gradualism, (b) Punctuated equilibrium

Image of Models of Speciation.

image of Models of speciation (a) Phyletic gradualism, (b) Punctuated equilibrium

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