NEET Biology Evolution 2027 — Darwin’s Theory, Natural Selection, Speciation and Practice Questions

Last Updated: April 2026

Evolution (NCERT Class 12 Biology, Chapter 7) is a consistent 2-4 question contributor in NEET 2027 Biology. While it requires conceptual understanding more than rote memorisation, the key theories, experiments, and examples must be precisely remembered. This guide covers the complete evolution chapter with Miller-Urey experiment, Darwin vs Lamarck debate, Hardy-Weinberg equilibrium, types of selection, speciation, and 30 NEET-level practice questions.

NEET Evolution — Topic-wise Weightage

1. Origin of Life

Oparin-Haldane Theory (Chemical Evolution)

• A.I. Oparin (1923) and J.B.S. Haldane (1929) proposed that life originated from inorganic molecules through a series of chemical reactions
• Early earth atmosphere: NH₃, CH₄, H₂O vapour, H₂ (reducing atmosphere, NO free oxygen)
• Energy: UV radiation, lightning
• Formation of organic molecules in the “primordial soup” (warm dilute ocean)

Miller-Urey Experiment (1953)

• Stanley Miller and Harold Urey experimentally tested Oparin-Haldane hypothesis
• Setup: closed flask with CH₄, NH₃, H₂, H₂O; electric sparks simulated lightning; water cooled and recycled
• Result: amino acids were synthesised within a week
• Significance: first experimental evidence that organic molecules can arise from inorganic compounds under early Earth conditions

First Life Form

• Life first appeared ~3.8 billion years ago
• First organisms: non-cellular (like viroids) → single-celled organisms (like bacteria)
• First self-replicating molecule: RNA (RNA world hypothesis) — RNA can act as both information carrier and catalyst (ribozyme)

2. Evolutionary Theories

Lamarck’s Theory (Inheritance of Acquired Characteristics)

• Jean-Baptiste Lamarck (1809) proposed that organisms evolve by use and disuse of organs
• Acquired characters (developed during an organism’s lifetime) are inherited by offspring
• Classic example: Giraffe’s neck lengthened by stretching → longer necks inherited by offspring
• Problem: Weismann’s experiment (cutting tails of mice for multiple generations — mice continued to be born with tails) disproved inheritance of acquired characters

Darwin’s Theory of Natural Selection (1859)

Charles Darwin, after his voyage on HMS Beagle (1831-1836), published “On the Origin of Species by Means of Natural Selection” (1859). Key postulates:

1. Overproduction: Organisms produce more offspring than can survive
2. Variation: Individuals in a population show heritable variations
3. Struggle for Existence: Resources are limited; individuals compete for survival
4. Survival of the Fittest (Natural Selection): Individuals with favourable variations survive and reproduce more
5. Inheritance: Favourable traits are inherited, increasing in frequency over generations
6. Speciation: Gradual accumulation of changes leads to new species

Fitness in Darwinian Sense

Fitness = reproductive fitness — the ability to leave more offspring that survive to reproduce. NOT about physical strength. A pale moth that survives better in a pale environment is more “fit” than a dark moth in the same environment.

Industrial Melanism — Classic NEET Example

• Before Industrial Revolution: Peppered moth (Biston betularia) — predominantly white (pale) form was camouflaged on pale bark of trees; dark form was eaten by predators
• After Industrial Revolution: soot darkened tree bark; dark (melanic) moths were now camouflaged; white moths became visible targets for predators
• Result: dark moths became predominant — evidence of Natural Selection in action

3. Hardy-Weinberg Equilibrium

In a large, randomly mating population with no disturbing factors, allele and genotype frequencies remain constant from generation to generation.

Hardy-Weinberg equation: p² + 2pq + q² = 1

• p = frequency of dominant allele (A)
• q = frequency of recessive allele (a)
• p + q = 1
• p² = frequency of AA, 2pq = frequency of Aa, q² = frequency of aa

Factors Disturbing Hardy-Weinberg Equilibrium (= Evolution in action)

1. Gene flow: migration of individuals between populations
2. Genetic drift: random change in allele frequency in small populations
3. Mutation: new alleles introduced
4. Non-random mating (sexual selection)
5. Natural selection

Genetic Drift

• Founder effect: new population established by few individuals (e.g., island colonisation). Small gene pool. Common in isolated communities.
• Bottleneck effect: large population reduced to few individuals by catastrophe (e.g., earthquake, disease). Remaining individuals have reduced genetic diversity.

4. Types of Natural Selection

5. Speciation

Formation of new species from existing ones. Types:

• Allopatric speciation: geographic isolation → reproductive isolation → new species. Most common. E.g., Darwin’s finches on Galapagos Islands
• Sympatric speciation: new species arise within the same geographic area, usually through reproductive isolation without physical barrier. E.g., polyploidy in plants

Reproductive Isolation Mechanisms

• Pre-zygotic: prevent mating or fertilisation (geographical, ecological, behavioural, temporal, mechanical, gametic isolation)
• Post-zygotic: hybrid inviability, hybrid sterility (mule = horse × donkey; sterile)

6. Types of Evolutionary Change

7. Human Evolution Timeline

Practice Questions — NEET Evolution

1. Miller-Urey experiment demonstrated that: (a) DNA was first life molecule (b) Amino acids can be synthesised under early Earth conditions (c) RNA was first evolved (d) Photosynthesis began life on Earth — Answer: (b)
2. Industrial melanism is an example of: (a) Lamarckian evolution (b) Directional Natural Selection (c) Genetic Drift (d) Convergent evolution — Answer: (b)
3. Hardy-Weinberg equilibrium is disturbed by: (a) Large population size (b) Random mating (c) Gene flow and genetic drift (d) Stable environment — Answer: (c)
4. Analogous structures indicate: (a) Divergent evolution (b) Convergent evolution (c) Common ancestry (d) Adaptive radiation — Answer: (b)
5. Darwin’s finches on Galapagos Islands are an example of: (a) Convergent evolution (b) Adaptive radiation (c) Stabilising selection (d) Founder effect — Answer: (b)
6. The first self-replicating molecule is believed to be: (a) DNA (b) Protein (c) RNA (d) Lipid — Answer: (c)
7. Homo habilis is significant because: (a) It was the first to use fire (b) It made stone tools (c) It had the largest brain (d) It buried the dead — Answer: (b)
8. Stabilising selection favours: (a) Both extremes (b) One extreme (c) The average phenotype (d) All phenotypes equally — Answer: (c)
9. Genetic drift is most significant in: (a) Very large populations (b) Very small populations (c) Populations under strong selection (d) Populations with high mutation rate — Answer: (b)
10. The Bottleneck effect reduces: (a) Population size only (b) Genetic diversity in a population (c) Natural selection (d) Mutation rate — Answer: (b)

Frequently Asked Questions (FAQ)

Related Reading: NEET Genetics Notes | NEET Ecosystem Chapter | NEET Human Reproduction