Biology · ZoologyZOO 07
Evolution
Darwin's theory, natural selection, evidence for evolution, Miller-Urey, human evolution
Concept Core
Essential theory — everything NCERT tests on Evolution
ORIGIN OF LIFE
Oparin & Haldane: 'hot dilute soup' theory — chemical evolution first. Miller-Urey experiment (1953): electric sparks through CH₄, NH₃, H₂O, H₂ → amino acids formed. Proved abiotic synthesis possible.
First life: chemoheterotrophs (used organic molecules). O₂ appeared ~2.5 Bya via cyanobacteria photosynthesis.
LAMARCK vs DARWIN
Lamarck: use and disuse + inheritance of acquired characters (WRONG). Example: giraffe's neck elongated by use.
Darwin: natural selection (survival of the fittest). Key elements: variation, overproduction, struggle for existence, differential survival & reproduction.
Darwin's finches: adaptive radiation. Dodo: example of extinction.
HARDY-WEINBERG PRINCIPLE
In ideal population, allele frequencies remain constant generation-to-generation. Conditions: large population, random mating, no mutation/migration/selection.
p² + 2pq + q² = 1; p + q = 1. Deviation from HWE = evolution occurring.
Agents of evolution: mutation, gene flow, genetic drift, natural selection, non-random mating.
EVIDENCE FOR EVOLUTION
Homologous organs: same structure, different function (same ancestry) — forelimbs of whale/bat/human. Indicates divergent evolution.
Analogous organs: different structure, same function — wings of bird vs butterfly. Convergent evolution.
Vestigial organs: non-functional remnants (human appendix, coccyx, ear muscles). Fossils: direct evidence.
HUMAN EVOLUTION
Dryopithecus (20 Mya): ape-like. Australopithecus (4–2 Mya): first hominid, walked upright, small brain. Homo habilis (2–1.5 Mya): first tool user. H. erectus (1.5 Mya): ate meat, larger brain. H. neanderthalensis (0.1–0.04 Mya): used hides, buried dead. H. sapiens: modern humans, 0.075 Mya onward.
Fact & Formula Vault
High-yield facts, numbers, and formulas
Key Events Timeline
4.6 Bya: Earth formed
3.8 Bya: First life (prokaryotes)
2.5 Bya: O₂ atmosphere (cyanobacteria)
500 Mya: Invertebrates (sea)
350 Mya: First amphibians on land
Hardy-Weinberg
p + q = 1 (allele freq)
p² + 2pq + q² = 1 (genotype freq)
HWE = no evolution occurring
5 agents cause deviation
Human Evolution
Australopithecus: 4–2 Mya, upright
Homo habilis: tool use, 2 Mya
Homo erectus: meat, fire, 1.5 Mya
H. sapiens: 0.075 Mya
Worked Examples
NEET-style questions solved step-by-step
EASYMiller-Urey experiment demonstrated:▾
Miller-Urey experiment demonstrated:
Abiotic synthesis of amino acids. Electric sparks passed through CH₄, NH₃, H₂O, H₂ (simulating early Earth atmosphere) → amino acids formed. Supported Oparin-Haldane chemical evolution theory.
MEDIUMWings of bat and wings of butterfly are:▾
Wings of bat and wings of butterfly are:
Analogous organs — same function (flight) but different structure and different evolutionary origin. This is convergent evolution. NOT homologous.
HARDIn a population, p = 0.6 (A) and q = 0.4 (a). What is the frequency of heterozygotes?▾
In a population, p = 0.6 (A) and q = 0.4 (a). What is the frequency of heterozygotes?
2pq = 2 × 0.6 × 0.4 = 0.48 (48%). Hardy-Weinberg: genotype frequencies = p² (AA) + 2pq (Aa) + q² (aa) = 0.36 + 0.48 + 0.16 = 1.
Mistake DNA
Common NEET traps for this chapter
⚠ Lamarck vs Darwin
Lamarck's inheritance of acquired characters is DISCREDITED. Darwin's natural selection is the accepted mechanism. Do not confuse the two.
✓ Fix: Darwin = natural selection (variation + differential survival), NOT Lamarck
⚠ Homologous vs Analogous
Homologous = same structure, different function = divergent evolution. Analogous = different structure, same function = convergent evolution. Whales + bats forelimb = homologous.
✓ Fix: Structure (anatomy) = homologous. Function = analogous.
⚠ HWE means no evolution
HWE only maintains frequencies if conditions are ideal. ANY deviation (mutation, drift, selection, migration) = evolution is occurring.
✓ Fix: HWE = null hypothesis of evolution. Deviation = evolution.
Chapter Intelligence
Exam data and last-minute strategy
NEET Frequency
2–3 Q/year. Miller-Urey experiment, HWE calculations, homologous vs analogous, human evolution timeline, and Darwin vs Lamarck are frequently tested.
High-Yield
p² + 2pq + q² = 1. Australopithecus = first upright walker. Homo habilis = first tool user. Analogous = convergent. Homologous = divergent. Miller-Urey → amino acids.
Strategy
Memorise the human evolution table (name, age, key feature). Practice HWE problems. Know 3 examples each of homologous and analogous organs.
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