Darwins Theory of Evolution


 
 
Concept Explanation
 

Darwins Theory of Evolution

Charles Darwin made a sea voyage around the world in a sailship HMS Beagle.

Based on his observations, he concluded the following

  • There has been gradual evolution of life forms with new forms arising at different periods of history.
  • Varying degrees of similarities can be observed between existing life forms and those existed million of years ago,
  • Population of all organisms have variations in characteristics, which make them adapt to better environment.
  • The characteristics which enable some population or individuals to survive better in natural conditions (foods, climate, physical factors) would outbreed others (survival of the fittest).
  • This fitness of the individual, according to Darwin, refers ultimately to the reproductive fitness. Such fit individuals leave more fit individuals than others. Thus, those organisms, which are better fit or adapt well will survive more in nature and will be selected by nature. This is called natural selection.

    Natural Selection

    It is based on following observations, which are factual

    (i) Limited natural resources due to which populations are stable in size except for seasonal fluctuations.

    (ii) Varying characteristics in members of a population, i.e., no two numbers of a population are identical even though they show similarities.

    (iii) Variations are generally inherited and population size will, exponentially.

    (iv) The population size is stable except seasonal fluctuations. It is due to the competition among the individual for resources

    Those which are better adapted could survive and will reproduce at the cost of others, i.e., who are less adapted the environment.

    Examples of natural selection are as follows

    Industrial Melanism

    Industrial melanism is an example of natural selection. There were collection of white moths in England. It was observed that before industrial revolution in England, white-winged moths were more in number than dark-winged moths. After industrialisation, dark-winged moths became more than white-winged moths.

    This is because during industrialisation, the tree trunks covered by white lichens became dark due to air pollution (dust and soot particles). Due to this, white-winged moths could be easily eaten by the predators as they failed in camouflaging (hide or disguise the presence of a person, animal or object by means of camouflage).

                               

    Chemical Resistance

    It is another example of natural selection.

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