Darwin's theory of natural selection

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Charles Robert Darwin was born in 1809. He traveled as a naturalist to Cape, Darvie, Atlantic Islands, Tahiti, New Zealand, Australia, Tasmania, etc. and collected a large number of specimens from these regions. In the light of these samples and his experience, he presented a revolutionary theory about the expression of organisms. Darwin's theory of natural selection is well established based on certain facts and conclusions. These facts are discussing below

High rate of reproduction The tendency to reproduce at a geometric rate is a characteristic of every organism. But not all offspring survive after reproduction. Many die in the fetal stage. Again several perish due to enemies, disease, competition, environment. Eventually only a few offspring survive. An E salmon fish lays about 2.8 million eggs during the breeding season. If every egg hatched and all the young survived, there would soon be an extreme problem with their habitat in the sea water. Then there was no other option but to leave the water and come up to the land. Darwin and Wallace called this struggle with nature to survive despite the high reproduction rate of life.

Food and space limitations: Food and habitat can rarely be changed except by artificial growth. The multiplicity of organisms is due to the ability of all organisms to reproduce at abnormal rates. In such a situation, multiple factors converge to eliminate organisms in excess of life-sustaining capacity. This results in overpopulation of organisms and obvious competition for survival.

Life Struggle: Due to geometrical and mathematical rate of reproduction and limited habitat and food, organisms have to undergo various difficult tests. This struggle of every life to survive is the struggle of life. This struggle is of three types. namely-

(a) Environmental Struggle: Every organism has to struggle in the face of natural calamities. For example, heavy rains, lack of rains, landslides, volcanic eruptions, epidemics, floods, extreme cold and extreme heat etc.

(b) Intraspecific struggle: The struggle that occurs between organisms of the same species for food, habitat, reproduction etc. is called intraspecific struggle or intraspecific conflict.

(c) Interspecies conflict: Conflict between different species is interspecies conflict or interspecies conflict.

No living thing on Earth is exactly the same. Variations can be seen between different members of the same species and even between the offspring of parents. According to Darwin, constant struggle results in many physical changes due to self-preservation.

Superiority of the fittest: In the struggle for life, only those who are fit to adapt to the environment will survive and reproduce. All other animals will become extinct. 6. Natural Selection: The most important aspect of Darwin's theory is natural selection.

Organisms with favorable differences or adaptive differences in processes have an added advantage in competition with others

It is called natural selection. Organisms with favorable characteristics, if selected by nature, survive in greater numbers and have the opportunity to reproduce more frequently. On the other hand, organisms with unfavorable traits slowly become extinct because they are not selected by nature. In explaining the theory of natural selection, Darwin resorted to artificial selection, sexual selection and imitation.

Consolidation of Species: Organisms selected by nature are allowed to live in succession and favorable differences in their bodies are carried on through generations.

Emergence of new species Due to the accumulation of favorable variations within a particular group of organisms, the contrast between the ancestral organism and the ancestor is greater and new species arise over time.

Criticism of the theory of natural selection:

Darwin considered instinct to be the main instrument of evolution. But he was unable to give a satisfactory explanation of how it takes place.

Darwin could not distinguish between the functions of somatic cells and reproductive cells in his theory.

Darwin's natural selection indicated the development and specialization of active organs but was unable to explain the presence of passive organs.

Darwin's theory should have been titled Natural Exclusion rather than 'Natural Selection'.

While speaking of the survival of the fit, he did not say anything about the non-appearance of the fit. Darwin dismissed mutation as a 'game of nature'.

According to Mendel's theory of mixed heredity, which Darwin spoke of, this is proven wrong. There is no discussion of how an organ functions in the first place of its origin.

^{I am a student of zoology and credit for this article goes to Madam Rita Parvin, Sir Shamol Shordar, Sir MD Rafikul Islam, Sir Shafiullah Shopon}

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