1. Introduction

  • Evolution is the gradual change in species over time.
  • It explains the origin of biodiversity and adaptation of organisms.
  • Key evolutionary mechanisms include natural selection, genetic drift, and mutation.
  • Modern evolutionary biology integrates genetics, paleontology, and molecular biology.

2. Darwin’s Theory of Natural Selection

  • Proposed by Charles Darwin in his book On the Origin of Species (1859).
  • Based on the idea of survival of the fittest.
  • Organisms with favorable traits are more likely to survive and reproduce.
  • Variation occurs naturally within populations.
  • Overproduction: Organisms produce more offspring than can survive.
  • Individuals compete for limited resources.
  • Beneficial traits get passed on to the next generation.
  • Over time, this leads to the formation of new species (speciation).

3. Evidence Supporting Evolution

  • Fossil records: Show transitional forms between species.
  • Comparative anatomy: Homologous structures suggest common ancestry.
  • Embryological evidence: Similar early development in different species.
  • Molecular biology: DNA and protein similarities indicate evolutionary relationships.
  • Biogeography: Distribution of species supports evolutionary history.

4. Modern Synthetic Theory of Evolution

  • Combines Darwin’s natural selection with Mendelian genetics.
  • Developed by scientists like Huxley, Mayr, Dobzhansky, Fisher.
  • Emphasizes the role of genetic variation, mutation, recombination, and selection.
  • Includes additional concepts such as genetic drift and gene flow.
  • Recognizes that mutations provide raw material for evolution.
  • Natural selection acts on genetic variation.
  • Isolation mechanisms lead to speciation.
  • Helps explain how evolution works at the molecular level.

5. Genetic Drift

  • Random changes in allele frequency in a small population.
  • Occurs due to chance events, not natural selection.
  • Leads to loss of genetic diversity.
  • Two major types:
    • Bottleneck effect: Drastic reduction in population size due to disasters.
    • Founder effect: A few individuals colonize a new area, leading to reduced genetic variation.
  • Can result in fixation or loss of alleles.
  • More significant in small populations.

6. Speciation and Evolutionary Patterns

  • Speciation is the formation of new species from existing ones.
  • Types of speciation:
    • Allopatric speciation: Due to geographic isolation.
    • Sympatric speciation: Occurs within the same habitat.
  • Evolutionary patterns:
    • Divergent evolution: Common ancestor gives rise to diverse species.
    • Convergent evolution: Unrelated species evolve similar traits.
    • Adaptive radiation: Rapid evolution of species from a common ancestor.

7. Conclusion

  • Darwin’s natural selection is a key mechanism of evolution.
  • Modern synthetic theory integrates genetics with evolution.
  • Genetic drift influences evolution in small populations.
  • Evolutionary biology explains the diversity of life on Earth.

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