The Synthetic Theory of Evolution #Zoology 3rd Sem #Unit....l

The modern theory of origin of species or evolution is the combination of Darwinism and Genetic Theory as well as the out come of mutationists , biometricians, naturalists, geneticists , experimental biologists ; and known as the synthetic theory of evolution .

   According to George Ledyard Stebbins five basic factors of organic evolution are (1)  gene mutation,

(2)  chromosomal abberations,

(3). genetic recombination,

(4)  natural selection and

(5). reproductive isolation.

            Factors 1,2 and 3 provide genetic variability  ;4 and 5 give direction to the evolution.

Migration and imigration  of an individual from a population to another  and hybridisation between races or close species increase genetic variability .Natural selection and chance elimination of alleles remove genes from gene pool during sexual reproduction.Genes of a gene pool are continuously reshuffled by genetic recombination.Alteration of gene frequency by natural selection results in evolution .Reproductive isolation  results in multidirectional evolution while absence of such isolation gives unidirectional evolution.

By 1950 synthetic theory of evolution was widely accepted by the scientists.