Darwinism – NEB Biology Notes XI

Darwinism NEB XI

In 1859, Darwin published his book the origin of species:
Darwinism can be described as follows :

Over production of offspring

According to Darwinism population tend to multiply geometrically and living organisms have more reproductive power than required to maintain their number.

Struggle for existence

The organisms reproduced at very rapid rate but the foodna dspace on the earth is limited. As a result , start competition between the organisms havin similar requirements .This competion between the organisms for basic needs of life like food, space, etc. is known as struggle for existence, It may be:
Intraspecific(between the members of same species)
Interspecific(Between the members of different species)
Environmental(The struggle against unfavourable environmental condition like earthquake, valocano , flood)
In this struggle many individuals died before reaching the sexual maturity and only few individuals survive. So, struggle for existence maintains the number of organisms remains constant.

Variation

It is the difference between the individuals . It is common in nature, Variation may be continuous or discontinuous continuous variation means small indistinct changes while discontinuous variations are large scale changes,the variations may be useful, harmful or neutral. Darwin protposed that living organisms adopt to the changing environment due to useful continuous variations.

Nautral selection or survival of the fittest

Nature select only those oranisms which are with useful continuous variations and best adopted to the environment, while others are eliminated . In other words, we can say that nature select those individuals which are fit to survive.

Origin of Species

According to Darwinism , variation appear in every generation and are inherited from one generation to another. So , these variation are go on accumulating and after a number of generations variation become so prominent that the individual turns into a new species.

Read this one too :   Neo - Darwinism

Demerits of Darwinism

  1. He didn’t explained the causes of variation He said that continuous variation are mainly responsible for the evolution which is not true.

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