Modern Synthetic Theory of Evolution

This theory is based on studies of population genetics,systematics and researches in molecular genetics since 1920s.

Stebbins has given five processes as major sources of variations in his book The Process of Organic Evolution.
1.Gene Mutation-.
2.Changes in chromosome structure and number
3.Genetic recombination
4.Natural selection
5.Isloation

Mutations are recessive;randomness of mutation is due toits random adaptiveness:mutational effect must be slight.Severe mutational impact will cause great disharmony and danger to survival.Many mutations and their recombinations are required for the departure from one species to another with several inversions and translocations. The guiding factor is gene-environment interaction.

Chromosomal structural changes are delections,duplications,inversions and translocations.THe position effect is due to these factors.

Genetic recombination is the combination and permutation of different alleles it provides great variations;recombination enhances the effect of selective mutation.

Natural selection operates upon variations and sort fit populations,reject the unfit.Selection may be of gene,gene locus,locus groups,chromosome,genome and thus set megaevolutionary process to come into action.The rate of selection fluctuate depending upon the change in environment and the introduction or ouster of another compelling allele.Fitness is due to structural adaptivness which provides better exploitation of resources and reproductive success that enable courtship,mating,fertilization etc

Isolation arisis due to environmental aspects which are spatial,environmental and reproductive isolating mechanisms.Spatial isolation is characteristic of local population,local races and geographical races.Reproductive isolation is characteristic of biological species.Ecological isolation is a universal feature of the species.