Darwin Theory of Natural Selection MCQ - Practice Questions with Answers

• Darwin provided for the theory of natural selection based on his observation on finches, giant tortoise, insects, lizards, etc. on Galapagos Islands.
• He also incorporated inputs from the theory of human population growth given by T.R. Malthus as follows:
  • Population grows geometrically when unchecked whereas means of subsistence grows only arithmetically
  • There would be an imbalance due to overgrowing population and lesser means of subsistence
  • Some factors like hunger, epidemics, floods, etc. would cause the population to shrink to the desired level
• Darwin received the ideas from Alfred Wallace who was working on Malay Archipelago.
• Darwin put forth all these ideas in the Journal of Proceedings of Linnean Society in 1859.
• Darwin also published his observations in a book titled the “The Origin of Species by Natural Selection”. 
   

Principle of Natural Selection:

• The principle of natural selection is based on five important observations and three inferences mentioned below:

• Natural selection is the differential success in reproduction and its product is the adaptation of organisms to their environment.

• Over Production or Enormous Fertility:
  • Living organisms have an innate capacity to produce more individuals to ensure continuity of the race.
  • For example, an oyster may produce over 60-80 million eggs per year.
• Limited Food and Space:
  • Despite rapid multiplication of all types of species, food and space and other resources remain limited.
• Struggle for Existence:
  • Organisms multiply in a geometric ratio, while the food supply increases in an arithmetic ratio. 
  • This leads to intense competition between organisms to ensure living to obtain maximum amount of food and shelter.
  • Struggle exists at three levels:
    • Intraspecific struggle is the competition among individuals of the same species or closely related forms. This type of struggle is very severe as the need of the population is the same.
    • Interspecific struggle is the struggle between organisms of different species living together. Individuals of one species compete with other species for similar requirements.
    • Struggle with the environment means the various hazards of nature like extreme heat or cold, excess moisture or drought, storms, earthquakes, volcanoes eruptions, etc. also affect the survival of various organisms.
•  Variations amongst Organisms:
  • Differences that exist among organisms are called variations. Variations may be harmful, neutral or useful. 
  • Variations that are passed on from generation to generation are called heritable variations and these form the raw material for evolution.
• Survival of the Fittest:
  • During the struggle for existence, the individuals that exhibit variations beneficial in facing the environment will survive, while those that cannot face the hardship will be eliminated. 
  • Those organisms best able to survive and reproduce will leave more offspring than those unsuccessful individuals. This is referred to as survival of the fittest.
  • According to Darwin, the giraffe exhibited variations in the length of the neck and legs. 
  • When the grass on the ground became scarce, giraffes with long necks and legs had an advantage over those with shorter neck and legs, as they could feed on the tall trees. 
  • So these forms survived and reproduced and became abundant. 
  • Over a period of time, giraffes with short necks starved and became extinct.
• Origin of Species:
  • As a result of struggle for existence, variability and inheritance, individuals that are better adapted, survived and became abundant. 
  • Slowly over a period of time, this group, which was remarkably different from the original population, became established as a new species. 
  • This group is also subject to the same forces of change as their ancestors were and this process continues to give rise to new species.
  • Members of this group may possess variations that may be beneficial to them in another environment. 
  • As a result, two or more species may arise from a single ancestral species.