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Meaning of Evolution

  • The term "Evolution" was given by Herbert Spencer.

  • Evolution is defined as a process of slow and gradual change seen in an orderly fashion. In other words, evolution is the gradual change in heritable traits of living organism over a number of generation.
  • It means to unroll or to unfold or to reveal the hidden potential.
  • Darwin defined evolution as "Descent with modification".
  • Every kind of change is not evolution. Evolution is change between successive generation.
  • Life has stopped originating now because the environment now is not like that of primitive earth . It has changed from reducing to oxidizing environment. 
  • Evolution is often defined as formation of complex forms from simple form but Complexity is never the aim of evolution.
  • Aim of evolution is fitness of an organism with surrounding.
  • Had complexity been the aim of evolution the parasites would have vanished.
  • Parasite show simplification in structure in course of evolution.
  • Evolution means successful feeding and breeding.
  • Gene pool changes over a number of generation.

Unit of evolution

Driving force for evolutionNatural selection
Unit of natural selectionIndividual
Raw material for evolutionVariation
Ultimate source for variation


"Individual get selected and population get evolved".

  • Evolution is a continuous process. It never stops because environment is never constant.
  • There is no climax of evolution.
  • Evolution is not goal oriented.
  • It is not a direct process in terms of determinism.
  • It is a stochastic process (a process about which we cannot say with 100% accuracy and surety)

Doll's law / law of Evolutionary Irreversibility :

Evolution is irreversible . Evolution is progressive.