Major Theories of Biological Evolution

1. Lamarckism (Inheritance of Acquired Traits)

Proposed by: Jean-Baptiste Lamarck (1809, Philosophie Zoologique)
Idea: Environmental needs and use/disuse of organs cause structural changes, passed to the next generation.
Examples:
- Giraffe’s long neck: To reach high tree leaves.
- Loss of snake limbs: Due to disuse in burrows.
- Webbed feet in aquatic birds.
- Sharp claws in carnivores.
Refutation:
- Weismann’s experiment: Cutting mice tails for 20-22 generations didn’t eliminate tails.
- Ear/nose piercing in India not inherited.
Conclusion: Acquired traits are not always inherited; only germplasm carries traits.

Exam Tip: Giraffe and snake examples are common in MCQs. Memorize Weismann’s refutation.

Proposed by: Charles Darwin (1859, Origin of Species)
Idea: Organisms with favorable variations survive the struggle for existence, passing traits to the next generation, forming new species.
Key Points:
- High reproductive capacity.
- Struggle for existence: Intraspecific, interspecific, environmental.
- Variations.
- Survival of the fittest.
- Inheritance of favorable traits.
Examples: Galapagos finch beak shapes, peppered moth color change.

Exam Tip: Finch beaks and peppered moth are key for MCQs and descriptive questions.

Proposed by: Hugo de Vries.
Idea: Sudden genetic changes (mutations) create new species, unlike gradual evolution.
Examples: New colors/shapes in plants, new traits in animals.
Significance: Explains rapid evolution.

Exam Tip: Understand the difference between Darwin (gradual) and De Vries (sudden) for MCQs.

Proposed by: Julian Huxley, Dobzhansky, Mayr, etc.
Idea: Combines Darwin’s natural selection with Mendel’s genetics; mutations, gene flow, and genetic drift drive evolution.
Key Points:
- Mutations provide new traits.
- Natural selection favors adaptive traits.
- Gene flow and genetic drift add diversity.
Example: Antibiotic resistance in bacteria.

Exam Tip: Antibiotic resistance and gene flow are frequent MCQ topics.

Taxonomy: Similar structures group organisms (e.g., fish-Pisces, mammals-Mammalia).
Comparative Anatomy:
- Homologous organs: Same structure, different function (e.g., human arm, bat wing).
- Analogous organs: Different structure, same function (e.g., insect and bird wings).
- Vestigial organs: Unused organs (e.g., human appendix, coccyx).
Comparative Embryology: Early embryos are similar, indicating a common ancestor.
Connecting Links:
- Archaeopteryx: Reptile-bird.
- Platypus: Bird-mammal.
- Lungfish: Fish-amphibian.

Exam Tip: Archaeopteryx and appendix are popular in MCQs.