Neo – Darwinism

Neo – Darwinism

There have been modern changes in the theory of natural selection. These changes were made necessary by the discovery of Mendal’s law of heredity in 1900 and development in psytology. Mendel by his experience said that genes present in the chromosomes are responsible for the characters in the organisms and these are hereditary units.Variation in the living organisms due to genes recombination or ­­­­­crossing over during gamete formation.                                       

Heugo Devris pinted the term mutation for certain inheitable change and proposed mutation  theory of evolution. He proposed that new species rises from pre – existing species in a single generation be certain appearances of marked inheritance differences called mutation.                                       

The modern synthetic theory is mainly based on the darwins theory of natural selection and mutation theory of Heugo Devris . Thiss theory is a combined effort of a number scientist lke Marley, Haldane, Haldex, Stabbian etc . 

According to the Stabbain this theory is based on five basic factors:

  1. Gene Mutation
  2. Chormosomal Mutation
  3. Genetic Recombination
  4. Natural selection
  5. Reproductive Isolation

Gene mutation 

  • Change in the structure and sequence of genes in chromosomes

Chromosomal mutation

  • Change in the structure and number of chromosome

Genetic recombination

  • Change in the genes and chromosomes due to crossing over during gamete formation.
  • These three factors are responsible for the the variation and variation is the basic need of evolution.

Darwinism Natural selection

It operates through differential reproduction . It states that the organisms having beneficial variation and best adopted to the environment are selected by the nature and they reproduce at a higher rate and produce more offspring than those which are less adopted. If the differential reproduction continues for a number of generation, then the genes of those individuals which produce more offspring’s with become pre dominant in the gene pool of the population. The genetic variations are transmitted from one generation to another and after many generation. These variations accumulate to form new species .

Read this one too :   Evolution - Biology Notes Grade XI

Darwinim Reproductive Isolation

The organisms evolved from natural selection posses beneficial variation. So, it is necessary that these organisms separate from unchanged population so that , they do not reproduce with unchanged organisms. It help to keep their identity. If they interbreed mixing of their genotype occurs which results in the disappearance of differences between them.

Evidence in favour of natural selection ( Darwinism)

Darwin in his visit to Galapagos Island in south America . He found many species of finches , the had beak which varied in structure from one species to another. Darwin found that a species with a particular type of beak ate seeds while others fruit, insects, leaves , etc. According to their beak . They have had a common ancestor, most probably seed eating  finches because of the competition for seeds , they had flown to the different parts of the Island . In due course of time, their feeding habit and their beak structure gradually changed to suit the type of food they fed on.                               

This shows how nature modified the birds habit and ultimately brought a change in this structure over long period of time, these may turn all together into different species.

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