Introduction to Evolution

Evolution is a gradual change in natural things from one condition to another with the passage of time. This term was first given by Herbert Spencer (father of evolution).

Organic evolution

It is the evolution of living organisms from simple to complex form with the passage of time in response to changed environment. This concept was first developed by Charles Darwin(father of organic evolution). He describes evolution as "Descent with modification", it means evolution is an outcome of gradual modification. Some important factors playing role in evolution includes mutation, natural selection, isolation, genetic drift etc.

Pattern of Evolution

Microevolution

It is an insignificant or small-scale change in phenotype of organisms of same species in response to the environmental condition.

Macroevolution:

It is a significant or large-scale change in organisms with the passage of time that leads to the formation of new species. Example; Evolution of fish, amphibians, reptiles, birds and mammals.

Divergent evolution

It is the development or evolution of different functional structures from common ancestral forms. It means similar organisms undergo different modification while kept in different environmental condition. Eg; Flippers of a whale, forelimb of a horse, patagium of a bat.

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fig:Divergent evolution

Convergent evolution

It is the development or evolution of similar functional structures in unrelated organisms. It means unrelated organisms undergoes similar modification while kept in similar environmental condition. Eg; wings of butterfly and birds.

Parallel evolution

It is the development or evolution of similar functional structures in closely related organisms. It means closely related organisms undergo similar modification in the similar environment. Eg; flippers of whale and seal for swimming, limbs of horse and deer for fast swimming.

Progressive evolution

It is the evolution of the complex form of organisms from simpler one. Eg; evolution of multicellular from unicellular.

Retrogressive evolution

It is the evolution of a simpler form of organisms from the complex one. Eg; Evolution of the parasitic worm from the free-living ancestor.

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fig: convergent evolution