Ronald A. Fisher, John B. S. Haldane and Sewall Wright- which showed that mutation and natural selection together cause adaptive evolution.

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Disruptive Natural selection

Disruptive selection favors the survival of individuals at both extremes of a range, rather than the  intermediate.

Increase variance in the population because select those phenotype which are away from mean.

It maintain balance polymorphism and maximum selection coefficient value.

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Balance natural selection

Balancing selection is a type of natural selection that maintains genetic diversity in a population.

In balancing selection, two or more alleles are kept in balance, and therefore are  maintained in a population over the course of many generations.

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Evolution by natural selection occurs if variation must lead by Ecotypes. 

Ecophene is not be selected by natural selection

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Change in environmental condition is not necessary for natural selection.

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Genetic drift 

Genetic drift is an evolutionary force, in which allelic frequency change over generation Just by chance (sampling error). 

The deviations from the expected ratios are random, the direction of change is unpredictable.