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A group of organisms that share similar characteristics and can reproduce with each other to produce offspring is called Species .

  • During evolution when a new species is formed, we call it Speciation .
  • Once a new species is formed, the organisms can only reproduce with others in the same species.
  • They cannot biologically reproduce with organisms in older species.

Consider the following;


  • Here if you notice, a beetle of one population entered another population and reproduced with the organism of that population. 
  • So there was a movement of genes from one population to another.
  • This is called Gene Flow .
  • This was possible because the populations are only partly separated, not completely.


But if,


  • Here, the river has separated the populations even further.
  • Since the individuals of different populations cannot mate easily, gene flow between them will decrease.

Now consider a third situation:


  • Here, during reproduction or due to genetic drift , a new variety was introduced into the populations.
  • The eagles replacing crows altered the natural selection of beetles in one population.
  • Thus genetic drift and natural selection together resulted in 2 populations of beetles that are different from each other and are unable to reproduce even if they met.
  • This is the very essence of Speciation .

Other possible ways speciation can take place in:

  • DNA changes resulting in changes in the number of chromosomes , so germ cells cannot fuse.
  • New genetic variation resulting in mating of green females only with green males not red males. This further results in an increase in the population of green beetles.

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CA Maninder Singh is a Chartered Accountant for the past 13 years and a teacher from the past 17 years. He teaches Science, Economics, Accounting and English at Teachoo