Karnataka Board PUCPUC Science 2nd PUC Class 12

Evolution of Life Forms - a Theory

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Notes

Evolution of Life Forms:

  • The conventional religious literature tells us about the theory of special creation.
  • This theory has three connotations.
    (i) All living organisms (species or types) that we see today were created as such
    (ii) Diversity was always the same since creation and will be the same in the future also
    (iii) Earth is about 4000 years old
  • All these ideas were strongly challenged during the 19th century. 
  • Charles Darwin, during a sea voyage in H.M.S. Beagle (a sail ship), concluded that existing living forms share similarities to varying degrees not only among themselves but also with life forms that existed millions of years ago.
  • Many living forms became extinct just as new living forms arose, at different periods of the history of the earth as a gradual evolution of life forms has taken place.
  • Any population has built in variation in characteristics. The characteristics which enable some to survive better in natural conditions (climate, food, physical factors, etc.) would outbreed others that are less endowed to survive under such natural conditions.
  • According to Darwin, the fitness of the individual or population refers to reproductive fitness. Hence, the organisms which survive in an environment will leave more progeny than others and eventually will survive more. Therefore, these organisms are selected by nature. Darwin called this as theory of natural selection.
  • Alfred Wallace, a naturalist who worked in the Malay Archipelago had also come to similar conclusions during that time.
  • In due course of time, new type of organisms became recognizable. All the existing life forms, however, share similarities and have common ancestors. These ancestors were present at different epochs, periods, and eras.
  • The geological history of the earth correlates with its biological history of the earth.
  • A common permissible conclusion is that the earth is very old, not thousands of years as was thought earlier but billions of years old.
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