Evolution NEET Notes 2027: Key Points and PDF

Evolution is Chapter 6 of NCERT Class 12 Biology and part of Unit 7, Genetics and Evolution, of the NEET UG syllabus. These notes cover the origin of life, Darwin’s theory, evidences for evolution, adaptive radiation, the mechanism of evolution, the Hardy-Weinberg principle, the history of life forms and human evolution, with a free notes PDF.

Evolution NEET Notes

Section-wise key points from NCERT Chapter 6, comparison tables, high-yield facts and common mistakes for NEET 2027 revision.

Evolution at a Glance

The topic list follows the NEET UG 2026 syllabus released by the National Medical Commission (NMC) on 22 December 2025, which stays the reference until the 2027 syllabus is out. The full list is on the NEET syllabus page.

How did life originate?

Most scientists accept that chemical evolution, the formation of organic molecules from inorganic constituents, came before the first cellular forms of life.

• The universe is almost 13.8 billion years old; the Big Bang theory explains its origin. Earth formed about 4.5 billion years ago.
• Early earth had no atmosphere. Water vapour, methane, carbon dioxide and ammonia released from the molten mass covered the surface; UV rays split water, lighter H2 escaped, and the ozone layer formed.
• Life appeared about 500 million years after the earth formed, almost four billion years ago.
• Panspermia: units of life called spores were transferred to different planets, including earth; still favoured by some astronomers.
• Spontaneous generation (life from decaying matter) was dismissed by Louis Pasteur: in pre-sterilised flasks no life came from killed yeast, while in flasks open to air new organisms arose.
• Oparin (Russia) and Haldane (England) proposed that the first life came from pre-existing non-living organic molecules (e.g. RNA, protein) after chemical evolution, under high temperature, volcanic storms and a reducing atmosphere with CH4 and NH3.
• The first non-cellular forms of life may have arisen about 3 billion years ago as giant molecules; the first cellular forms probably did not arise until about 2000 million years ago, all in water.

Miller’s Experiment (1953)

• S.L. Miller, an American scientist, created electric discharge in a closed flask with CH4, H2, NH3 and water vapour at 800 °C.
• He observed the formation of amino acids. Others later observed sugars, nitrogen bases, pigments and fats in similar experiments.
• Meteorite analysis showed similar compounds, suggesting such processes also occur elsewhere in space.

Special Creation Versus Darwin’s Theory

The theory of special creation says all living organisms were created as such, diversity has always been the same, and earth is about 4000 years old; these ideas were strongly challenged in the nineteenth century.

• Charles Darwin drew his conclusions from observations during a voyage round the world on the sail ship H.M.S. Beagle.
• Existing life forms share similarities with each other and with forms that lived millions of years ago; many forms have gone extinct while new forms arose.
• Populations have built-in variation; individuals better fitted to natural conditions outbreed others.
• Fitness, according to Darwin, refers ultimately and only to reproductive fitness: the fitter leave more progeny and are selected by nature (natural selection).
• Alfred Wallace, who worked in the Malay Archipelago, reached similar conclusions around the same time.
• Conclusion: earth is billions of years old, not thousands.

What are the evidences for evolution?

Evidence comes from fossils (palaeontology), embryology, comparative anatomy and morphology, biochemical similarities, artificial selection and natural selection seen in action.

• Palaeontological evidence: fossils are remains of hard parts of life forms in rocks. Different-aged sediments hold different life forms, showing that new forms arose at different times. Fossil ages are found by radioactive dating.
• Embryological evidence was proposed by Ernst Haeckel: all vertebrate embryos, including human, have a row of vestigial gill slits behind the head, functional only in fish. Karl Ernst von Baer disproved this, noting that embryos never pass through the adult stages of other animals.
• Biochemical evidence: similarities in proteins and genes performing a given function in diverse organisms point to common ancestry.
• Artificial selection: humans created distinct breeds (e.g. dogs) within hundreds of years, so nature could do the same over millions of years.

Industrial Melanism and Anthropogenic Evolution

• In England, moths collected in the 1850s (before industrialisation) were mostly white-winged; collections from the same area in 1920 had more dark-winged (melanised) moths.
• Industrial smoke and soot darkened tree trunks, so predators picked out white-winged moths; earlier, white lichen on trees hid white moths and exposed dark ones.
• Lichens are industrial pollution indicators because they do not grow in polluted areas. In rural areas melanic moth counts stayed low.
• No variant is completely wiped out; the better-adapted ones increase in number.
• Excess use of herbicides, pesticides, antibiotics and drugs has selected resistant varieties within months or years: evolution by anthropogenic action.
• Evolution is not directed; it is a stochastic process based on chance events in nature and chance mutation.

What is adaptive radiation?

Adaptive radiation is the evolution of different species in a given geographical area starting from a point and radiating to other habitats.

• Darwin’s finches on the Galapagos Islands are one of the best examples: from the original seed-eating finches, forms with altered beaks arose, becoming insectivorous and vegetarian.
• Australian marsupials: many different marsupials evolved from an ancestral stock within the Australian island continent.
• When more than one adaptive radiation occurs in an isolated geographical area, it can be called convergent evolution.
• Placental mammals in Australia also show adaptive radiation, each resembling a corresponding marsupial, e.g. the placental wolf and the Tasmanian wolf (marsupial).

Biological Evolution: Darwin’s Natural Selection

The essence of Darwinian theory is natural selection; branching descent and natural selection are its two key concepts.

• Evolution by natural selection began when cellular forms with differences in metabolic capability arose.
• Example: in a bacterial colony (A), a change in medium lets only a part of the population (B) survive; B outgrows the rest and appears as a new species within days. In fish or fowl the same would take millions of years.
• Fitness is based on inherited characteristics, so selection needs a genetic basis. Adaptive ability is inherited.
• Darwin may have been influenced by the work of Thomas Malthus on populations.
• Factual observations behind natural selection: resources are limited, population sizes are stable except for seasonal fluctuation, members vary, and most variation is inherited.
• Since populations could grow exponentially but stay limited, there is competition; heritable variations that make resource use better let some leave more progeny, so population characteristics change over generations.

Lamarck’s View

• Jean-Baptiste Lamarck, a French naturalist, said evolution was driven by the use and disuse of organs.
• His example: giraffes stretching for leaves on tall trees elongated their necks and passed this acquired character on.
• NCERT states that nobody believes this conjecture any more.

Mechanism of Evolution: Variation and Mutation

Darwin spoke of small heritable variations, while Hugo de Vries, working on evening primrose, said that large sudden mutations cause evolution.

Later studies in population genetics brought more clarity: variation from mutation, recombination during gametogenesis, gene flow or genetic drift changes allele frequencies, and natural selection acts on this variation.

Hardy-Weinberg Principle

The Hardy-Weinberg principle states that allele frequencies in a population are stable and constant from generation to generation; this genetic equilibrium means the gene pool stays constant.

• Gene pool: total genes and their alleles in a population. The sum of all allele frequencies is 1.
• For a gene with alleles A (frequency p) and a (frequency q): p + q = 1.
• Genotype frequencies: AA = p², Aa = 2pq, aa = q², so p² + 2pq + q² = 1, the binomial expansion of (p + q)².
• Worked example: if 16 per cent of a population is aa, q² = 0.16, so q = 0.4, p = 0.6, AA = 0.36 and Aa = 2 × 0.6 × 0.4 = 0.48.
• If measured frequencies differ from expected values, the difference shows the extent of evolutionary change. Disturbance of the equilibrium means evolution.

Types of Natural Selection

A Brief Account of Evolution

NCERT traces life from the first cells about 2000 million years ago (mya) to mammals, using these approximate dates.

• Lobefins evolved into the first amphibians, ancestors of modern frogs and salamanders. A Coelacanth, thought to be extinct, was caught in South Africa in 1938.
• Amphibians evolved into reptiles, which lay thick-shelled eggs that do not dry up in the sun; turtles, tortoises and crocodiles are their modern descendants.
• Tyrannosaurus rex, the biggest dinosaur, was about 20 feet tall with dagger-like teeth.
• The first mammals were shrew-like and viviparous. When South America joined North America through continental drift, its mammals were overridden by North American fauna; Australia’s pouched mammals survived for lack of competition.
• Some mammals live wholly in water: whales, dolphins, seals and sea cows.

Origin and Evolution of Man

Human evolution runs from ape-like primates about 15 mya through Australopithecines and Homo habilis to Homo erectus, the Neanderthals and Homo sapiens.

• Pre-historic cave art developed about 18,000 years ago; cave paintings can be seen at the Bhimbetka rock shelter in Raisen district, Madhya Pradesh.
• Agriculture came around 10,000 years ago and human settlements started.
• The skull of a baby chimpanzee is more like an adult human skull than an adult chimpanzee skull (NCERT Figure 6.11).

Most-asked Facts for NEET: Evolution

Revise these one-line facts from the NCERT chapter just before the exam.

• Universe: about 13.8 billion years old; earth: about 4.5 billion years.
• Pasteur’s killed-yeast experiment disproved spontaneous generation.
• Oparin and Haldane proposed chemical evolution.
• Miller (1953): CH4, H2, NH3 and water vapour, electric discharge, 800 °C; amino acids formed.
• Darwin’s fitness means reproductive fitness.
• Wallace worked in the Malay Archipelago and reached similar conclusions.
• Haeckel proposed embryological evidence; von Baer disproved it.
• Homology = divergent evolution; analogy = convergent evolution.
• Thorn of Bougainvillea and tendril of Cucurbita are homologous.
• Sweet potato and potato are analogous.
• Industrial melanism: more dark moths after industrialisation (1920) than before (1850s).
• Darwin’s finches and Australian marsupials are examples of adaptive radiation.
• Hugo de Vries worked on evening primrose; saltation is single-step large mutation.
• Hardy-Weinberg: p² + 2pq + q² = 1.
• Five factors affecting Hardy-Weinberg equilibrium: gene flow, genetic drift, mutation, recombination, natural selection.
• Coelacanth was caught in South Africa in 1938.
• Brain sizes: Homo habilis 650-800 cc, Homo erectus about 900 cc, Neanderthal about 1400 cc.
• Bhimbetka rock shelter (Raisen, Madhya Pradesh) has pre-historic cave paintings.

Common Mistakes to Avoid

Watch for these mix-ups when you answer questions on this chapter.

• Calling homologous organs a result of convergent evolution. Homology comes from divergent evolution; analogy from convergent evolution.
• Classing sweet potato and potato as homologous. One is a root and the other a stem modification, so they are analogous.
• Thinking Miller’s experiment produced living cells. It produced amino acids, supporting chemical evolution only.
• Equating Darwinian fitness with strength. Fitness means reproductive fitness: leaving more progeny.
• Treating Lamarck’s use-and-disuse idea as accepted. NCERT says nobody believes it any more.
• Using q² as the allele frequency. In Hardy-Weinberg, q is the allele frequency and q² the frequency of the homozygous recessive genotype.
• Forgetting the 2 in 2pq when finding the heterozygote frequency.
• Confusing gene flow (repeated migration) with genetic drift (chance change in allele frequency, as in the founder effect).
• Saying industrial melanism wiped out white moths. No variant is completely wiped out; only the proportions change.
• Mixing up hominid brain sizes or dates: Homo habilis 650-800 cc, Homo erectus about 900 cc (about 1.5 mya, Java), Neanderthal about 1400 cc.

Evolution Notes PDF and Related Pages

Download the AglaSem notes for Evolution (key notes and important questions with answers) free: View PDF

• All chapters: NEET Biology notes
• Full topic list: NEET syllabus
• Practice: NEET question papers
• Source text: NCERT Chapter 6 (NCERT, Class 12 Biology)

NEET Biology Notes: All Chapters

Botany

• The Living World
• Biological Classification
• Plant Kingdom
• Cell: The Unit of Life
• Plant Growth and Development
• Anatomy of Flowering Plants
• Cell Cycle and Cell Division
• Respiration in Plants
• Photosynthesis in Higher Plants
• Morphology of Flowering Plants
• Principles of Inheritance and Variation
• Microbes in Human Welfare
• Sexual Reproduction in Flowering Plants
• Molecular Basis of Inheritance
• Organisms and Populations
• Ecosystem
• Biodiversity and Conservation

Zoology

• Animal Kingdom
• Biomolecules
• Breathing and Exchange of Gases
• Excretory Products and their Elimination
• Body Fluids and Circulation
• Structural Organisation in Animals
• Locomotion and Movement
• Reproductive Health
• Chemical Coordination and Integration
• Neural Control and Coordination
• Evolution
• Human Health and Disease
• Human Reproduction
• Biotechnology and its Applications
• Biotechnology: Principles and Processes

All chapters with their notes PDFs are on the NEET Biology notes page.

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