Class 12 Biology Evolution Evidences for evolution

Evidences for evolution

Evidences of evolution comes from-

Paleontological evidence-

  • Paleontology is the study of fossils.
  • Fossils are remains of hard parts of life forms lived in past but found in rocks or sediments.
  • Rocks from sediments and a cross section of earth’s crust indicates the arrangement of sediments one over the other during the long history of earth.
  • Different aged rock sediments contain fossils of different life forms that probably died during the formation of the particular sediment which represent extinct organisms.
  • A study of fossils in different sedimentary layers indicates the geological period in which the organisms existed.
  • The study showed that life forms varied over time and certain life forms are restricted to certain geological time spans.
  • New forms of life have arisen at different times in the history of earth.

Fig. fossils  


Comparative anatomy and morphology-

  • Comparative anatomy and morphology shows similarities and differences among organisms of today and those that existed years ago.

Homologous organs-

  • The organs whose structure or origin is same but functionally different. Example-  i) Vertebrate hearts or brains.  ii) In plants, the thorns and tendrils of Bougainvillea and Cucurbita.   iii) The fore limbs of whale, bats, cat and human share similarities in the pattern of forelimb bones.
  • All the animals have similar anatomical structure in their fore limb bones such as humerus, radius, ulna, carpals, metacarpals and phalanges.
  • Though the forelimbs have similar anatomical structure but they perform different functions.
  • The same structure developed along different directions due to adaptations to different needs.
  • Homology is based on divergent evolution.
  • Homology indicates common ancestry.

Fig. forelimbs of human, cat, whale and bat  

Analogous organs-

  • The organs whose structure or origin is not similar but functionally active are called analogous organs. Example- i) The wings of bird and butterfly perform similar functions. ii) Eye of octopus and mammals.              iii) The flippers of penguins and dolphins. iv) In plants, sweet potato and potato.
  • Similarities in proteins and genes performing a given function among diverse organisms give clues to common ancestry.
  • It is the similar habitat that has resulted in selection of similar adaptive features in different groups of organism but towards the same function.

Fig. flippers of whale and bat  


Natural selection-

Industrial melanism-

  • Before industrialization, in Great Britain it was observed that there were more white winged moths on trees than dark or melanised moth.
  • After industrialization, there were more dark-winged moths.
  • Before industrialization, almost white-coloured lichen covered the tree trunks and in that background the white-winged moths survived but the dark coloured moths were eaten by predators.
  • During post industrialization period, the tree trunks became dark due to industrial smoke and under such condition the white- winged moths did not survive sue to predators and the dark- winged moths’ survived hence industrial melanism supports evolution by natural selection.


Fig. white and black winged moths  

Antibiotic resistant bacteria

  • By employing antibiotics to bacterial colonies, the colonies sensitive to penicillin died, whereas the others that were resistant to penicillin survived.
  • Probably the bacteria that survived underwent a chance mutation there by possessing a gene that contributed to their resistance to the penicillin drug and hence selected by the nature, in course of time was considered as fittest and established as new species.

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