Three general models were proposedfor abortive transcription.

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#Unit 11. Evolution and Behavior

Populational change is Darwin’s hypothesis that evolution occurs by changes in the proportions (frequencies) of different variant kinds of individuals within a population.

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#Id: 3162

#Unit 11. Evolution and Behavior

Natural selection was Darwin’s brilliant hypothesis, independently conceived by Wallace, that accounts for adaptations, features that appear “designed” to fit organisms to their environment.

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#Id: 3163

#Unit 11. Evolution and Behavior

 Orthogenesis- “Straight-line evolution,” held that the variation that arises is directed toward fixed goals.

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#Id: 3164

#Unit 11. Evolution and Behavior

Mutationist- Theories were advanced by some geneticists who observed that discretely different new phenotypes can arise by a process of mutation.

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#Id: 3165

#Unit 11. Evolution and Behavior

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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#Id: 3166

#Unit 11. Evolution and Behavior

 Neutral theory of molecular evolution- Developed by Motoo Kimura, who argued that most of the evolution of DNA sequences occurs by chance (genetic drift) rather than by natural selection.