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Evolution — BIOLOGY STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 ScienceBIOLOGYEvolution5 Marks
Question
  1. Explain Darwinian theory of evolution with the help of one suitable example.
  2. State the two key concepts of the theory.
  3. Amongst pea tendril, Opuntia spines, lemon thorn and Cucurbita tendrils, which ones are homologous structures. Why do you call them so?
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Answer

  1. Any population has built in variation for every character.

Individuals with those characters which enable them to survive better in the given environment, would outbreed the others, who are less adapted. Fitness, according to Darwin, is reproductive fitness, i.e. individuals who are more fit in an environment leave more progeny than others.

These progenies survive better and more and more fit individuals are added to the population, i.e. natural selection.

The population thus comes to possess more fit individuals, i.e. nature selects the better fit invididuals and over a long period of time, through a number of generations, the population slowly becomes modified into a different form or a species, in the process called evolution, e.g. evolution of DDT-resistant mosquitoes.

  1. The two key concepts of Darwinian theory are:
  • Branching descent.
  • Natural selection.
  1.  
  • Lemon thorn and Cucurbita tendrils are homologous-as both are stem modified
  • Opuntia spines and pea tendrils are homologousas both are leaf modifications.
  • Homologous organs are those organs in different groups of organisms, that are similar in basic structural and developmental patterns, but perform different functions and are superficially distinct.

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