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Introduction of Evolution

Evidences of Evolution of Class 12

Evolution (term by Herbert Spencer 1856) is a slow continuous, irreversible and natural process of change to give rise to advance and diverse forms of life.

Term comes from ‘revolvere’ that means to unfold or unroll, as life is process of “going on’. From bacteria to man and from diatoms to trees there are wide differences yet they share some common features. The change in the properties of population through generations is the biological or organic evolution. Darwin (1859) defined it as the “descent with modification”. Dobzhansky (1973) said “nothing in biology makes sense except in the light of evolution”.

Ideas before Darwin

The ancient Indian Literature like Ayurveda deals with origin of life; Manu Samhita mentions about evolution.  The ancient Greek thoughts (2000 yrs before Darwin) like of Plato (428 - 348 BC) believed species as unchanging ideal form (eidos)Aristotle (384 - 322 BC) also believed in fixitiveness of species like Plato but extended his ideas of diversity in a chain or ladder like series progressing from most imperfect to most perfect. He named it as “Ladder of Nature” or “Scala Naturae” or “Great chain of Being”

Introduction of Evolution

Several evidences convince that modern diverse forms of organisms have arisen by evolution from more ancient forms. Following are the main evidences.

  • Evidences from Taxonomy
  • Evidences from Connecting links
  • Evidences from Morphololgy & Comparative anatomy
  • Evidences from Physiology & Biochemistry
  • Evidences from Embryology
  • Evidences from Cytology & Genetics
  • Evidences from Palaeontology
  • Evidences from Biogeography
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