NCERT Solutions for Class 12 Biology Chapter 6 Evolution
NCERT Solutions for Class 12 Biology Chapter 6 Evolution provides detailed study notes and answers covering Origin of Life, Evidences for Evolution, Darwinism, Adaptive Radiation, Hardy-Weinberg Principle, Mechanisms of Evolution, and Human Evolution.
Overview of Topics & Subtopics (Click to Jump)
1. Origin of Life & Evidences for Evolution
Short Note:
• Origin of Life: Universe originated around 20 billion years ago (Big Bang Theory). Earth formed 4.5 billion years ago. Life appeared 500 million years after formation of Earth (~4 billion years ago).
• Miller Experiment (1953): S.L. Miller created primitive Earth conditions in spark discharge apparatus containing CH4, NH3, H2, and H2O vapor at 800°C. Formation of amino acids proved chemical evolution hypothesis of Oparin and Haldane.
• Evidences of Evolution:
1. Homologous Organs: Same structure/origin but different function (Divergent Evolution). E.g., Forelimbs of Whales, Bats, Cheetah, and Humans.
2. Analogous Organs: Different structure/origin but same function (Convergent Evolution). E.g., Wings of Butterflies and Birds, Eyes of Octopus and Mammals.
2. Theories of Evolution & Adaptive Radiation
Short Note:
• Theories of Evolution:
- Lamarckism: Theory of inheritance of acquired characters (use and disuse of organs, e.g., Giraffe neck).
- Darwinism: Natural Selection (Branching Descent and Survival of the Fittest based on natural variations).
- Mutation Theory: Proposed by Hugo de Vries working on Evening Primrose (Oenothera lamarckiana). Mutations are random, directionless, and cause speciation in single step (Saltation).
• Adaptive Radiation: Process of evolution of different species in a given geographical area starting from a point and radiating to other habitats. E.g., Darwin's Finches in Galapagos Islands, Australian Marsupials.
3. Hardy-Weinberg Principle & Human Evolution
Short Note:
• Hardy-Weinberg Principle: Allele frequencies in a population are stable and constant from generation to generation in absence of evolutionary factors. Algebraic equation: p² + 2pq + q² = 1.
- Factors Affecting Equilibrium: Gene migration/gene flow, Genetic drift (Founder effect), Mutation, Genetic recombination, and Natural Selection.
• Human Evolution Stages:
1. Dryopithecus & Ramapithecus: 15 mya (Ramapithecus was more man-like).
2. Australopithecines: 2 mya in East African grasslands (used stone weapons, ate fruit).
3. Homo habilis: First human-like hominid (Brain capacity 650–800 cc, did not eat meat).
4. Homo erectus: 1.5 mya (Brain capacity 900 cc, ate meat).
5. Neanderthal Man: 100,000–40,000 years ago (Brain capacity 1400 cc, used hides, buried dead).
6. Homo sapiens: Arose in Africa 75,000–10,000 years ago during Ice Age.
Intext & Conceptual Questions
| Feature | Homologous Structures | Analogous Structures |
|---|---|---|
| Anatomy / Origin | Same basic anatomical structure and embryonic origin. | Different anatomical structure and embryonic origin. |
| Function | Adapted to perform different functions. | Adapted to perform similar functions. |
| Pattern of Evolution | Indicates Divergent Evolution. | Indicates Convergent Evolution. |
| Example | Forelimbs of Whales, Bats, Cheetah, and Humans. | Wings of Birds and Insects; Eyes of Octopus and Mammals. |
Adaptive Radiation: It is the evolutionary process in which different species evolve from a common ancestral stock and diversify to adapt to different ecological niches/habitats.
Examples:
1. Darwin's Finches: On the Galapagos Islands, Darwin observed many varieties of small black birds. From an original seed-eating ancestor, different varieties evolved with altered beak shapes adapted to eating seeds, insects, cactus, etc.
2. Australian Marsupials: A number of distinct marsupials (e.g., Kangaroo, Koala, Tasmanian wolf) evolved from a single ancestral stock within the Australian island continent.
Textbook Chapter End Exercise Questions
Miller's Experiment (1953): Stanley Miller created experimental conditions similar to primitive Earth atmosphere in a laboratory setup:
1. He used a closed glass apparatus containing methane (CH4), ammonia (NH3), hydrogen (H2), and water vapor.
2. Electric sparks were discharged using electrodes at 800°C to simulate lightning.
3. After running the experiment for a week, he observed the formation of simple organic compounds including amino acids (such as glycine, alanine, aspartic acid).
Significance: It provided experimental proof for Oparin-Haldane's theory of Chemical Evolution (Abiogenesis followed by Biogenesis).
Hardy-Weinberg Principle: States that allele frequencies in a large, randomly mating population remain constant from generation to generation, provided no evolutionary influences act on it. Represented as:
p² + 2pq + q² = 1 (where p and q are frequencies of dominant and recessive alleles).
Factors Disturbance Equilibrium:
1. Gene Migration / Gene Flow: Movement of genes into or out of a population.
2. Genetic Drift: Random changes in allele frequency by chance events (e.g., Founder Effect).
3. Mutation: New alleles introduced by genetic mutations.
4. Genetic Recombination: Crossing over during meiosis.
5. Natural Selection: Differential reproduction favoring certain genotypes.
The sequential stages of human evolution are:
1. Dryopithecus & Ramapithecus (15 mya): Ape-like and man-like hominids.
2. Australopithecines (2 mya): Walked upright, lived in grasslands, used stone tools.
3. Homo habilis (2 mya): First human-like hominid, brain capacity 650–800 cc.
4. Homo erectus (1.5 mya): Walked fully erect, brain capacity 900 cc, ate meat.
5. Neanderthal Man (100,000–40,000 years ago): Brain capacity 1400 cc, used hides, buried dead.
6. Homo sapiens (75,000–10,000 years ago): Modern humans, developed agriculture, art, and civilization.
Read More & Chapter Resources
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