Paleontological evidence:

  • Fossils are remained of hard parts of life-forms found in rocks.
  • Different-aged rock sediments contain fossils of different life-forms who probably died during the formation of the particular sediment.
  • They represent the extinct organisms (e.g. Dinosaurs).
  • A study of fossils in different sedimentary layers indicates the geological period in which they existed.
  • The study showed that life-forms varied over time and certain life forms are restricted to certain geological time-span.
  • Hence new lives have arisen at different times in the history of earth.
  • All this called Paleontological evidence.

Comparative anatomy and morphological evidence:

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

Divergent evolution:

  • Whale, bats, cheetah and human share similarities in the pattern of bones of forelimbs.
  • These forelimbs perform different functions in these animals, they have similar anatomical structure – all of them have humerus, radius, ulna, carpals, metacarpals and phalanges in their forelimbs.
  • Hence in these animals, the same structure developed along different directions due to adaptation to different needs.
  • This is divergent evolution and these structures are homologous.
  • Homology indicates common ancestry.
  • Other examples of homologous organ are vertebrate hearts and brains.
  • Thorn of Bougainvillea and tendrils of Cucurbita are present homology.

Convergent evolution:

  • Wings of butterfly and of birds look alike.
  • They are anatomically similar structure though they perform similar function.
  • Hence analogous structures are a result of convergent evolution.
  • Eye of octopus and eye of mammals.
  • Flippers of Penguins and Dolphins.
  • Sweet potato (root modification) and potato (stem modification).

Biochemical evidences:

  • Similarities in proteins and genes performing a given function among diverse organisms give clues to common ancestry.

 Embryological support for evolution:

  • Proposed by Ernst Haeckel based upon observation of certain features during embryonic stage common to all vertebrates that are absent in adult.
  • The embryos of all vertebrates including human develop a row of vestigial gill slits just behind the head but it is a functional organ only in fish and not found in any other adult vertebrates.
  • This is disproved on careful study performed by Karl Ernst von Baer. He noted that embryos never pass through the adult stages of other animals.

Evolution by natural selection:

  • Based on observation of moth population in England made in 1850.
  • Before industrialization set in, it was observed that there were more white-winged moths on trees than dark-winged or melanised moths.
  • After industrialization i.e. 1920 there were more dark-winged moths in the same area i.e. the proportion was reversed.

Evolution by anthropogenic action:

  • Excess use of herbicides, pesticides etc., has only resulted in selection of resistant varieties in a much lesser time scale.
  • This is also true for microbes against which we employ antibiotics or drugs against eukaryotic organisms/cell.
  • Hence resistance organisms/cells are appearing in a time scale of months or years and not in centuries.
  • These are the examples of evolution by anthropogenic action.
  • Evolution is a stochastic process based on chance events in nature and chance mutation in the organisms.

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