Evolution — Class 12 Biology NCERT Solutions (Free)

Free step-by-step NCERT solutions for Class 12 Biology chapter "Evolution" — 5 important questions with detailed answers for CBSE board exam preparation.

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TL;DR: Free step-by-step NCERT solutions for Class 12 Biology chapter "Evolution" — 5 important questions with detailed answers for CBSE board exam preparati…

Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated Jul 23, 2026

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Key Questions Covered:

Define evolution. Explain the evidence for evolution from paleontology, compa…
State and explain Darwin's theory of natural selection with examples.
Define speciation. Explain different modes of speciation with examples.
Explain Hardy-Weinberg principle and its application in population genetics.
Explain the concept of genetic drift and its effects on small and large popul…

Solutions Summary:

Question	Status
Define evolution. Explain the evidence for evolution from…	✓ Solved
State and explain Darwin's theory of natural selection wi…	✓ Solved
Define speciation. Explain different modes of speciation …	✓ Solved
Explain Hardy-Weinberg principle and its application in p…	✓ Solved
Explain the concept of genetic drift and its effects on s…	✓ Solved

Showing 5 of 5 questions

Q1: Define evolution. Explain the evidence for evolution from paleontology, comparative anatomy, and molecular biology.

Evolution: Change in heritable characteristics of populations over successive generations. Gradual modification of organisms over time resulting in formation of new species. Based on descent with modification from common ancestors. Evidence for evolution: 1. Paleontological evidence (Fossil records): - Fossils show progression of forms over geological time - Intermediate forms connect major groups: Archaeopteryx (dinosaur-bird), Tiktaalik (fish-tetrapod) - Transitional fossils show gr...

Q2: State and explain Darwin's theory of natural selection with examples.

Charles Darwin's theory of natural selection (1859) explains mechanism of evolution. Key observations: 1. Variation: Individuals in population show variation in traits - Example: some beetles dark, some light colored - Variation heritable and passed to offspring 2. Overproduction: Organisms produce more offspring than environment can support - Example: fish lay millions of eggs; few survive to reproduce - Population growth limited by resources (food, space, mates) 3. Struggle for...

Q3: Define speciation. Explain different modes of speciation with examples.

Speciation: Process of evolution of new species from existing species. Formation of reproductive isolation preventing gene flow between populations. Results in separate species that cannot interbreed. Species concept (Biological definition): - Groups of actually or potentially interbreeding wild populations - Share common gene pool - Reproductive isolation from other species - Cannot produce fertile offspring with other species Reproductive isolation mechanisms: 1. Prezygotic barriers (preven...

Q4: Explain Hardy-Weinberg principle and its application in population genetics.

Hardy-Weinberg principle: In absence of evolutionary forces, allele and genotype frequencies remain constant from generation to generation in large, randomly mating population. Foundation of population genetics. Mathematical statement: For two alleles (A and a) with frequencies p and q: - p + q = 1 (where p = frequency of A, q = frequency of a) - Genotype frequencies: p² (AA) + 2pq (Aa) + q² (aa) = 1 Example: If A frequency = 0.7 and a frequency = 0.3 - AA frequency = (0.7)² = 0.49 - Aa frequ...

Q5: Explain the concept of genetic drift and its effects on small and large populations.

Genetic drift: Random changes in allele frequencies in populations due to chance events. Random sampling of alleles in reproduction. Causes unpredictable, non-directional changes in gene frequencies. Mechanism: - In finite populations, random variations occur in mating and reproduction - Some alleles by chance passed to more offspring than others - This random variation changes allele frequency - Effect stronger in small populations - Different from natural selection: occurs regardless of allel...

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