NEET Biology — Evolution Complete Chapter Guide

Chapter Overview & Weightage

Evolution covers the origin of life, evidences of evolution, theories (Lamarckism, Darwinism, Modern Synthetic Theory), Hardy-Weinberg equilibrium, adaptive radiation, and human evolution. This chapter is more conceptual than most NEET biology — understanding beats memorisation here.

This chapter carries 3-4% weightage in NEET with 2-3 questions. Hardy-Weinberg principle, homologous vs analogous organs, and human evolution timeline are the most tested areas.

Key Concepts You Must Know

Tier 1 (Core)

Evidences of evolution: homologous organs (divergent evolution), analogous organs (convergent evolution), fossils, embryological evidence
Darwin’s theory: natural selection, survival of the fittest, variation, overproduction
Hardy-Weinberg equilibrium: $p^2 + 2pq + q^2 = 1$ and $p + q = 1$
Five factors that disturb HW equilibrium: gene flow, genetic drift, mutation, natural selection, non-random mating

Tier 2 (Frequently tested)

Adaptive radiation: evolution of diverse species from a common ancestor (Darwin’s finches, Australian marsupials)
Types of natural selection: stabilising, directional, disruptive
Industrial melanism: example of natural selection in action (peppered moth)
Speciation: allopatric (geographic isolation), sympatric (reproductive isolation without geographic barrier)

Tier 3 (Occasionally tested)

Origin of life: Oparin-Haldane hypothesis, Miller-Urey experiment
Human evolution: Dryopithecus → Ramapithecus → Australopithecus → Homo habilis → Homo erectus → Homo sapiens
Lamarckism vs Darwinism comparison

Important Formulas

For a gene with two alleles (dominant $p$ , recessive $q$ ):

p + q = 1 \quad \text{(allele frequencies)}

p^2 + 2pq + q^2 = 1 \quad \text{(genotype frequencies)}

Where:

$p^2$ = frequency of homozygous dominant (AA)
$2pq$ = frequency of heterozygous (Aa)
$q^2$ = frequency of homozygous recessive (aa)

Application: If 16% of a population shows the recessive phenotype, then $q^2 = 0.16$ , so $q = 0.4$ , $p = 0.6$ . Carrier frequency ( $2pq$ ) = $2 \times 0.6 \times 0.4 = 0.48 = 48\%$ .

Feature	Homologous	Analogous
Origin	Same embryonic origin	Different embryonic origin
Function	Different functions	Similar function
Evolution	Divergent evolution	Convergent evolution
Example	Forelimbs of whale, bat, human	Wings of insect and bird
Indicates	Common ancestry	Similar environment/selection pressure

Hardy-Weinberg numerical problems are the only “calculation” questions in this chapter. The trick: always find $q$ first (from the recessive phenotype frequency, which equals $q^2$ ). Then get $p = 1 - q$ . Everything else follows.

Solved Previous Year Questions

PYQ 1 — NEET 2024

Problem: In a population in Hardy-Weinberg equilibrium, if the frequency of the recessive allele is 0.3, what is the frequency of the heterozygous genotype?

Solution:

$q = 0.3$ , so $p = 1 - 0.3 = 0.7$

Heterozygous frequency: $2pq = 2 \times 0.7 \times 0.3 = \mathbf{0.42}$ (or 42%)

Answer: 0.42

PYQ 2 — NEET 2023

Problem: Wings of butterfly and wings of bird are:

(A) Homologous (B) Analogous (C) Vestigial (D) Atavistic

Solution:

Wings of butterfly (insect, no bones, made of chitin) and wings of bird (vertebrate, modified forelimb with bones) perform the same function (flight) but have completely different structural origins. This is convergent evolution — they are analogous organs.

Answer: (B) Analogous

PYQ 3 — NEET 2022

Problem: Which of the following is an example of adaptive radiation?

(A) Peppered moth (B) Darwin’s finches (C) Industrial melanism (D) Drug resistance in bacteria

Solution:

Darwin’s finches on the Galapagos Islands are the textbook example of adaptive radiation — a single ancestral species diverged into multiple species with different beak shapes adapted to different food sources.

Peppered moth and industrial melanism are examples of natural selection (directional). Drug resistance is also natural selection.

Answer: (B) Darwin’s finches

Difficulty Distribution

Difficulty	% of Questions	What to Expect
Easy	40%	Homologous vs analogous identification, theory matching
Medium	40%	Hardy-Weinberg calculations, natural selection types
Hard	20%	Human evolution sequence, speciation mechanisms

Expert Strategy

Day 1: Evidences of evolution — homologous vs analogous (with 3-4 examples each), vestigial organs, embryological similarities. These are the easiest marks in the chapter.

Day 2: Hardy-Weinberg principle — do 5-6 numerical problems. The formula is simple, but NEET varies the question framing: sometimes they give $q^2$ , sometimes $p$ , sometimes the heterozygous frequency. Practice all formats.

Day 3: Human evolution timeline and adaptive radiation examples. For human evolution, memorise the sequence and one key feature of each stage (brain size increase, tool use, bipedalism).

For human evolution, remember the brain volume progression: Australopithecus (~500 cc) → Homo habilis (~700 cc) → Homo erectus (~900 cc) → Homo sapiens (~1400 cc). NEET tests this ascending order.

Common Traps

Trap 1 — Homologous organs have DIFFERENT functions, not similar. The forelimbs of a whale (swimming), bat (flying), and human (grasping) are homologous — same origin, different functions. Students confuse this because “homologous” sounds like “same.”

Trap 2 — Hardy-Weinberg equilibrium requires NO evolution. HW equilibrium is the null hypothesis — no mutation, no selection, no migration, random mating, large population. Any deviation from HW indicates evolution is occurring.

Trap 3 — Lamarck’s theory of inheritance of acquired characters is wrong. But NEET tests whether you know what Lamarck proposed (even though it was incorrect). Don’t dismiss the theory entirely — know it well enough to compare with Darwin’s.

Trap 4 — Genetic drift is significant in SMALL populations, not large ones. Founder effect and bottleneck effect are types of genetic drift. They cause random changes in allele frequency — not adaptive, just random. NEET tests the population size condition.