The basic conclusions of Darwin’s theory of natural selection are briefly mentioned.
- High rate of reproduction: High rate of reproduction is an inherent characteristic of organisms. It increases the number of organisms at a geometric and mathematical rate. A salmon fish lays 30 million eggs per season, a hilsa fish lays about 20 lakh eggs.
- Habitat and food limitation: With the increase in the number of organisms there are habitat and food limitations. Natural resources like light, air, water, food etc. are less than the number of living beings. So the food and habitat of the organism is limited.
- Life Struggle: The competition of organisms for food, water, shelter and other beneficial elements is called life struggle. Life struggles are of three types.
(i) Intra-species struggle: Struggle between members of the same species is called intra-species struggle. Deer-deer struggle, buffalo-buffalo struggle, tiger-tiger struggle etc. intra-species struggle.
(ii) Interspecies struggle: Struggle between members of different species is called interspecies struggle. Interspecies struggle like tiger and deer struggle, snake and frog struggle, lion and buffalo struggle.
(iii) Environmental Struggle: The struggle to survive and save life in a hostile environment is called ecological struggle. The struggle to protect against floods, droughts, storms, heavy rains, cold currents, epidemics, floods, cyclones, earthquakes, eruptions, fires is an environmental struggle.
- Variation or Parivritti: Variation is the difference in shape and character among different members of the same species. Variation is permanent and heritable. Only those variations that are able to adapt to the unfavorable environment survive.
- Victory of the fittest: Favorable variants are able to adapt to adverse environments and survive in competition. The fittest varieties survive well. It is called the victory of the fittest. Organisms that lose the competition gradually become extinct. Because of this, dinosaurs became extinct.
- Natural selection and creation of new species: Nature selects those species or varieties which are able to easily adapt to changing and adverse environment. They reproduce at high rates. Nature re-selects them through inheritance. Thus over the ages they are selected by nature and new species are created.
