Theories of Evolution | Zoology Optional Notes for UPSC PDF Download

Lamarckism

• Proposed by French biologist Jean-Baptiste de Monet Lamarck.
• Lamarckism, introduced in 1801 and elaborated in the book "Philosophic Zoologique" (1809), posits that physical changes acquired by an individual during its lifetime are inherited by offspring.
• Lamarck's Four Propositions:
  • Internal Vital Force
  • Effect of Environment and New Needs
  • Use and Disuse of Organs
  • Inheritance of Acquired Characters.
• Examples include the elongation of giraffe necks due to stretching for leaves, webbed toes in aquatic birds, and limb disappearance in snakes.
• Criticisms: Lack of vital force, dubious environmental influence, and disputed inheritance of acquired traits.

Darwinism

• Proposed by English naturalist Charles Robert Darwin.
• Darwin's Theory of Natural Selection (1859) emphasizes:
  • Overproduction and differential reproduction.
  • Struggle for existence involving intraspecific, interspecific, and environmental challenges.
  • Variations, with beneficial traits passed on to offspring through natural selection.
  • Formation of new species through continuous useful variations.
• Criticisms: Doesn't explain inheritance of small variations, overspecialization, vestigial organs, arrival of the fittest, degeneration of organs, and discontinuous variations.

Mutation Theory

• Proposed by Dutch botanist Hugo de Vries.
• States that new species arise from sudden inheritable variations (mutations) that don't revolve around the species' mean character.
• Key Points:
  • Mutations are raw material for evolution, appearing suddenly and can lead to new species.
  • Nature selects useful mutations; lethal ones are eliminated, but harmless ones persist.
  • Mutations occur in all directions and are inheritable.
• Evolution is a discontinuous process, marked by jerky changes.

Synthetic Theory of Evolution

• The modern evolutionary synthesis combines Darwinian natural selection and Mendelian genetics.
• It integrates genetic variation, natural selection, and mutation, providing a comprehensive understanding of evolutionary processes.
• This synthesis forms the basis of contemporary evolutionary biology, unifying various aspects of evolution into a coherent framework.