Neo-Darwinism “OR” Modern Synthetic Theory of Organic Evolution
Neo-Darwinism is the modified form of Darwinism. This theory is modification of Darwin`s theory along with cytological and genetical information regarding the organic evolution. This is based upon the following facts:- Mutation:- Sudden heritable changes that occur in the chemistry of genetic material of organisms are known as mutation. It can bring drastic change in offspring and lead to origin of new organisms. Basically, mutations are of two types: gene mutation and chromosomal mutation. Both gene and chromosomes determine the characteristics of organisms. So the sudden change in them can lead to variation of characters of offspring. Useful variation leads to better adaptation while harmful variation leads to extinction of the organisms. Thus, mutation produces variations in offspring. Genetic recombination: Genetic recombination is the nature of genetic variations caused by reshuffling of genes during sexual productions or gamete formation. In other words, it is the production of new gene types from already existing genes. Recombination are of the following types:- The productions of gene combination containing in the same individuals of two different alleles of same gene or the productions of heterozygous individuals (meiosis). The random mixing of chromosomes from two parents to produce a new individual (sexual reproduction). Mixing of a particular allele with a series of genes not previously associated with it, by an exchange between chromosomal pars during meiosis, called crossing over to produce new gene combinations.
Natural Selections: According to this theory, nature does not itself brings variations in the organisms but supports the useful variations. That means natural selection does not produce genetic change, but once the genetic change has taken place, it acts to encourage some gene over other. It rejects weaker ones and supports the winners during adaptations. Thus, natural selection guides the population towards adaptation. Reproductive Isolations: According to this, when the potential mates are isolated by various factors such as geographical locations, physiological factors etc. for a long time, then after the long time their inter- breeding capability is lost. This phenomenon is known as reproductive isolation. Migration and hybridization helps to increase the genetic variability to the population which may lead to formation of new species. Genetic drift: This means the random changes in the frequency of gene in a gene pool. It does not occur by natural selection, rather occurs by chance. This is when there is alternation in the number of organisms among small population, due to factors like migration, epidemics etc. genetic drift occurs.