I. ORIGIN OF LIFE
A THE UNIVERSE & EARTH
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| FEATURE | DETAIL |
|---|---|
| Evolutionary Biology | Study of history of life forms on earth ⭐ |
| Stellar distances | Measured in light years ⭐ |
| Origin of universe | ~13.8 billion years old (some notes say ~20 billion) ⭐ |
| Universe composition | Huge clusters of galaxies → contain stars + clouds of gas & dust ⭐ |
| Big Bang Theory | Explains origin of universe — singular huge explosion → expansion → temperature dropped → H₂ & He formed → gases condensed under gravitation → galaxies formed ⭐⭐ |
| Origin of Earth | ~4.5 billion years ago ⭐⭐ |
| Origin of life | ~4 billion years ago (500 million years after Earth formed) ⭐⭐ |
B EARLY EARTH CONDITIONS
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| FEATURE | DETAIL |
|---|---|
| No atmosphere initially | On early earth ⭐ |
| Gases released from molten mass | Water vapour, CH₄ (methane), CO₂, NH₃ (ammonia) ⭐ |
| UV rays | Broke water into H₂ and O₂; lighter H₂ escaped ⭐ |
| O₂ combined with | NH₃ and CH₄ → formed water, CO₂ and others ⭐ |
| Ozone layer | Formed subsequently ⭐ |
| Water vapour | Fell as rain → filled depressions → formed oceans ⭐ |
| Atmosphere type | Reducing atmosphere (containing CH₄, NH₃, water vapour) ⭐ |
C THEORIES OF ORIGIN OF LIFE
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| THEORY | PROPONENT | KEY IDEA |
|---|---|---|
| Special Creation | Religious literature | (1) All organisms created as such; (2) Diversity always same; (3) Earth ~4000 years old ⭐ |
| Spontaneous Generation | Ancient belief | Life came from decaying/rotting matter (straw, mud, etc.) ⭐ |
| Biogenesis | Louis Pasteur | Life comes only from pre-existing life ⭐⭐ |
| Panspermia | Early Greek thinkers | Units of life (spores) transferred to different planets including Earth ⭐ |
| Chemical Evolution (Abiogenesis) | Oparin (Russia) & Haldane (England) | First life from pre-existing non-living organic molecules (RNA, protein); formation of life preceded by chemical evolution ⭐⭐⭐ |
⚡ EXAM TRAP: NEET 2022
Panspermia — spores transferred to different planets including Earth.
Louis Pasteur Experiment ⭐⭐
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| FEATURE | DETAIL |
|---|---|
| Used | Pre-sterilised flasks ⭐ |
| Showed | In pre-sterilised flasks → no life from killed yeast; in flask open to air → new organisms arose ⭐ |
| Dismissed | Spontaneous generation theory — once and for all ⭐ |
| Limitation | Did NOT answer how the first life form came on earth ⭐ |
🔑 SEQUENCE OF CHEMICAL EVOLUTION: (1) Synthesis of organic monomers → (2) Synthesis of organic polymers → (3) Formation of protobionts → (4) Formation of DNA-based genetic systems
⚡ EXAM TRAP: NEET 2016
Sequence — monomers → polymers → protobionts → DNA-based systems.
D MILLER–UREY EXPERIMENT (1953)
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| FEATURE | DETAIL |
|---|---|
| Scientist | S.L. Miller (American scientist) ⭐ |
| Year | 1953 ⭐ |
| Purpose | Created conditions similar to early Earth in laboratory ⭐ |
| Apparatus | Closed flask ⭐ |
| Gases used | CH₄ (methane), H₂ (hydrogen), NH₃ (ammonia), Water vapour ⭐⭐ |
| Energy source | Electric discharge (simulating lightning) ⭐ |
| Temperature | 800°C ⭐ |
| Products observed | Amino acids ⭐⭐ |
| Others observed | Sugars, nitrogen bases, pigments, fats ⭐ |
| Meteorite analysis | Revealed similar compounds → similar processes occurring in space ⭐ |
⚡ EXAM TRAP: NEET 2020
Miller's experiment — CH₄, H₂, NH₃, water vapour at 800°C → amino acids formed.
E FIRST LIFE FORMS
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| FEATURE | DETAIL |
|---|---|
| First non-cellular forms | Could have originated ~3 billion years ago ⭐ |
| Nature | Giant molecules — RNA, Protein, Polysaccharides ⭐ |
| First cellular forms | Originated ~2000 million years ago (mya) ⭐ |
| Type | Probably single-celled ⭐ |
| Environment | All life forms were in water only ⭐ |
| First organisms | Non-green and presumably anaerobes ⭐ |
| First autotrophs | Chemoautotrophs (never released oxygen) ⭐ |
| Some cells could | Release O₂ (reaction similar to light reaction of photosynthesis) ⭐ |
⚡ EXAM TRAP: NEET 2016
First organisms = non-green, anaerobes; First autotrophs = chemoautotrophs (never released O₂).
II. EVOLUTION OF LIFE FORMS — DARWIN'S THEORY
A CHARLES DARWIN
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| FEATURE | DETAIL |
|---|---|
| Ship | H.M.S. Beagle (sail ship) ⭐ |
| Observation | Existing living forms share similarities to varying degrees — among themselves AND with life forms from millions of years ago ⭐ |
| Built-in variation | Any population has built-in variation in characteristics ⭐ |
| Fitness | According to Darwin = ultimately & only reproductive fitness ⭐⭐ |
| Natural Selection | Those better fit in an environment leave more progeny → survive → selected by nature ⭐⭐⭐ |
| Two key concepts | (1) Branching descent & (2) Natural selection ⭐⭐ |
| Influenced by | Thomas Malthus (work on populations) ⭐ |
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| SCIENTIST | DETAIL |
|---|---|
| Alfred Wallace | Naturalist; worked in Malay Archipelago; reached similar conclusions around same time ⭐ |
⚡ EXAM TRAP: NEET 2013
Darwin — natural selection, competition, survival of fittest.
⚡ EXAM TRAP: NEET 2020
Darwin's ship = H.M.S. Beagle.
B NATURAL SELECTION — KEY OBSERVATIONS
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| OBSERVATION | DETAIL |
|---|---|
| Natural resources | Limited ⭐ |
| Populations | Stable in size except for seasonal fluctuations ⭐ |
| Members | Vary in characteristics (no two individuals alike) ⭐ |
| Variations | Most are inherited ⭐ |
| Population growth | Would grow exponentially if all reproduced maximally ⭐ |
| Reality | Population sizes limited → competition for resources ⭐ |
| Result | Only some survived → changed population characteristics → new forms arise ⭐ |
C LAMARCK'S THEORY
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| FEATURE | DETAIL |
|---|---|
| Scientist | Lamarck (French naturalist) ⭐ |
| Theory | Evolution driven by use and disuse of organs ⭐ |
| Example | Neck of Giraffes — elongated by foraging on tall trees → passed on to succeeding generations ⭐ |
| Status | Nobody believes this conjecture anymore ⭐ |
D THEORY OF SPECIAL CREATION — THREE CONNOTATIONS
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| CONNOTATION | DETAIL |
|---|---|
| 1 | All living organisms created as such ⭐ |
| 2 | Diversity was always the same since creation & will remain same ⭐ |
| 3 | Earth is about 4000 years old ⭐ |
| Status | Strongly challenged during 19th century ⭐ |
III. EVIDENCES FOR EVOLUTION
⚡ EXAM TRAP: RE-NEET 2026
Palaeontological evidence from fossil records and divergent evolution of anatomical structures (homologous forelimbs) are valid evidences of evolution; convergent evolution does not prove common ancestry.
A PALAEONTOLOGICAL EVIDENCE (FOSSILS)
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| FEATURE | DETAIL |
|---|---|
| Fossils | Remains of hard parts of life-forms found in rocks ⭐ |
| Study of fossils | Palaeontology ⭐ |
| Rock sediments | Different-aged sediments contain fossils of different life-forms ⭐ |
| Finding | Life-forms varied over time; certain forms restricted to certain geological time-spans ⭐ |
| Dating method | Radioactive dating ⭐ |
B EMBRYOLOGICAL EVIDENCE
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| FEATURE | DETAIL |
|---|---|
| Proposed by | Ernst Haeckel ⭐ |
| Observation | Certain features during embryonic stage common to all vertebrates but absent in adults ⭐ |
| Example | Embryos of all vertebrates develop a row of vestigial gill slits behind the head — functional organ only in fish ⭐ |
| Disapproved by | Karl Ernst von Baer ⭐⭐ |
| His observation | Embryos never pass through adult stages of other animals ⭐ |
⚡ EXAM TRAP: NEET 2020
Ernst Haeckel — embryological support; Karl Ernst von Baer — disapproved (embryos never pass through adult stages of other animals).
⚡ EXAM TRAP: RE-NEET 2026
Haeckel's embryological support for evolution was later disapproved by Karl Ernst von Baer — it is no longer accepted as valid evidence.
C COMPARATIVE ANATOMY — HOMOLOGY & ANALOGY
Homologous Organs (Divergent Evolution) ⭐⭐⭐
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| FEATURE | DETAIL |
|---|---|
| Definition | Same anatomical structure but different functions ⭐⭐ |
| Origin | Same (common) ancestry ⭐ |
| Based on | Divergent evolution ⭐ |
| Significance | Homology indicates common ancestry ⭐ |
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| EXAMPLE | DETAIL |
|---|---|
| Forelimbs of mammals | Whale, Bat, Cheetah, Human — similar bone pattern (humerus, radius, ulna, carpals, metacarpals, phalanges) but different functions ⭐⭐⭐ |
| Vertebrate hearts | Homologous ⭐ |
| Vertebrate brains | Homologous ⭐ |
| Thorn of Bougainvillea & Tendril of Cucurbita | Homologous (in plants) ⭐⭐ |
⚡ EXAM TRAP: NEET 2014, 2018, 2022
Forelimbs of mammals = homologous; Thorn (Bougainvillea) & Tendril (Cucurbita) = homologous.
⚡ EXAM TRAP: RE-NEET 2026
Forelimbs of humans and bats are homologous because they have a similar anatomical structure (humerus, radius, ulna, carpals, metacarpals, phalanges) — same structure, different function, common ancestry.
⚡ EXAM TRAP: NEET 2026
Forelimbs of whales and bats represent divergent evolution (homologous), not convergent evolution.
Analogous Organs (Convergent Evolution) ⭐⭐⭐
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| FEATURE | DETAIL |
|---|---|
| Definition | NOT anatomically similar but perform similar functions ⭐⭐ |
| Origin | Different ancestry ⭐ |
| Based on | Convergent evolution — different structures evolving for the same function ⭐ |
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| EXAMPLE | DETAIL |
|---|---|
| Eye of Octopus & Mammals (Cat) | Analogous ⭐⭐ |
| Flippers of Penguins & Dolphins | Analogous ⭐⭐⭐ |
| Sweet potato (root) & Potato (stem) | Analogous ⭐⭐ |
| Wings of Butterfly & Birds | Analogous ⭐⭐ |
⚡ EXAM TRAP: NEET 2013, 2014, 2020, 2022, 2024
Analogous examples — Eye of octopus & mammals; Flippers of penguins & dolphins; Sweet potato & potato; Wings of butterfly & birds.
⚡ EXAM TRAP: NEET 2026
Eyes of octopuses and mammals, wings of butterflies and birds, and flippers of penguins and dolphins are all examples of convergent evolution.
⚡ EXAM TRAP: NEET 2025
Sweet potato (modified root) and potato (modified stem) = Analogy, convergent evolution.
D HOMOLOGY vs ANALOGY — COMPARISON
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| FEATURE | HOMOLOGOUS | ANALOGOUS |
|---|---|---|
| Anatomical structure | Same ⭐ | Different ⭐ |
| Function | Different ⭐ | Same ⭐ |
| Ancestry | Common ⭐ | Different ⭐ |
| Evolution type | Divergent ⭐ | Convergent ⭐ |
| Example (Animals) | Forelimbs of mammals | Flippers of Penguins & Dolphins |
| Example (Plants) | Thorn (Bougainvillea) & Tendril (Cucurbita) | Sweet potato & Potato |
E BIOCHEMICAL EVIDENCE
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| FEATURE | DETAIL |
|---|---|
| Similarities in | Proteins and genes performing given function among diverse organisms ⭐ |
| Points to | Same shared ancestry as structural similarities ⭐ |
F INDUSTRIAL MELANISM — NATURAL SELECTION IN ACTION
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| FEATURE | DETAIL |
|---|---|
| Location | England ⭐ |
| Type of natural selection | Directional selection ⭐ |
| Before industrialisation (1850s) | More white-winged moths on trees than dark-winged (melanised) moths ⭐ |
| After industrialisation (1920) | More dark-winged moths in the same area; proportion reversed ⭐ |
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| EXPLANATION | DETAIL |
|---|---|
| Post-industrialisation | Tree trunks became dark due to industrial smoke and soot ⭐ |
| White-winged moths | Did NOT survive (spotted by predators against dark background) ⭐ |
| Dark-winged moths | Survived (camouflaged against dark background) ⭐ |
| Before industrialisation | White-coloured lichens covered trees → white moths survived; dark moths picked by predators ⭐ |
| Lichens | Known as pollution indicators — do NOT grow in polluted areas ⭐⭐ |
| Rural areas | Where industrialisation did NOT occur → count of melanic moths was low ⭐ |
| Key principle | Those that can better-adapt, survive and increase in population ⭐ |
| No variant | Is completely wiped out ⭐ |
⚡ EXAM TRAP: NEET 2015
Industrial Melanism = example of natural selection (directional).
G EVOLUTION BY ANTHROPOGENIC ACTION
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| FEATURE | DETAIL |
|---|---|
| Cause | Excess use of herbicides, pesticides, antibiotics, drugs ⭐ |
| Result | Selection of resistant varieties in much lesser time scale (months/years, not centuries) ⭐ |
| Examples | Antibiotic-resistant bacteria; herbicide-resistant weeds; drug-resistant eukaryotic organisms ⭐ |
| Man-created breeds | Dogs (intensive breeding → new breeds but same group) ⭐ |
| Key concept | Evolution is NOT a directed process — it is a stochastic process (based on chance events & chance mutations) ⭐⭐ |
⚡ EXAM TRAP: NEET 2020, 2021
Anthropogenic action → resistant varieties; evolution is stochastic (NOT directed).
IV. ADAPTIVE RADIATION
A DEFINITION
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| FEATURE | DETAIL |
|---|---|
| Definition | Process of evolution of different species in a given geographical area starting from a point and literally radiating to other geographical areas (habitats) ⭐⭐⭐ |
⚡ EXAM TRAP: NEET 2012, 2021, RE-NEET 2024
Adaptive radiation — evolution of different species from a point, radiating to other areas.
B DARWIN'S FINCHES
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| FEATURE | DETAIL |
|---|---|
| Location | Galapagos Islands ⭐⭐ |
| Observed by | Darwin during his voyage ⭐ |
| Description | Small black birds; many varieties on same island ⭐ |
| Original feature | Seed-eating ⭐ |
| Evolved into | Insectivorous and vegetarian forms with altered beaks ⭐ |
| Evolved where | On the island itself ⭐ |
| Status | One of the best examples of adaptive radiation ⭐ |
⚡ EXAM TRAP: NEET 2013, 2020, 2021
Darwin's Finches — seed-eating → insectivorous & vegetarian; Galapagos Islands; best example of adaptive radiation.
C AUSTRALIAN MARSUPIALS
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| FEATURE | DETAIL |
|---|---|
| Type | Another example of adaptive radiation ⭐ |
| Evolved from | Ancestral stock ⭐ |
| Where | All within the Australian island continent ⭐ |
| Survived because | Lack of competition from any other mammal (due to continental drift) ⭐ |
Marsupial Examples ⭐
Marsupial mole • Numbat (Anteater) • Marsupial mouse • Spotted Cuscus • Flying Phalanger • Tasmanian Tiger Cat • Tasmanian Wolf
D CONVERGENT EVOLUTION OF PLACENTAL & MARSUPIAL MAMMALS
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| FEATURE | DETAIL |
|---|---|
| When | More than one adaptive radiation in an isolated geographical area (different habitats) ⭐ |
| Result | Convergent evolution ⭐ |
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| PLACENTAL MAMMAL | AUSTRALIAN MARSUPIAL |
|---|---|
| Mole | Marsupial mole ⭐ |
| Anteater | Numbat (Banded Anteater) ⭐ |
| Mouse | Marsupial mouse ⭐ |
| Lemur | Spotted Cuscus ⭐ |
| Flying Squirrel | Flying Phalanger ⭐ |
| Bobcat | Tasmanian Tiger Cat ⭐ |
| Wolf | Tasmanian Wolf ⭐ |
⚡ EXAM TRAP: NEET 2023, 2024
Convergent evolution of Australian Marsupials & Placental Mammals; know the pairs (e.g., Wolf ↔ Tasmanian Wolf; Flying Squirrel ↔ Flying Phalanger).
⚡ EXAM TRAP: RE-NEET 2026
Adaptive radiation in placental mammals and Australian marsupials, leading to similarity between distant species, is an example of convergent evolution.
V. MECHANISM OF EVOLUTION
A DARWIN vs HUGO DE VRIES
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| FEATURE | DARWIN | HUGO DE VRIES |
|---|---|---|
| Century | 19th century | 20th century ⭐ |
| Organism studied | Various | Evening Primrose (Oenothera lamarckiana) ⭐ |
| Variations | Small & Directional ⭐ | Random & Directionless (Mutations) ⭐⭐ |
| Evolution | Gradual ⭐ | Jerky (sudden) ⭐ |
| Cause of speciation | Natural selection (minor variations) | Mutations ⭐ |
| Term used | — | Saltation (single step large mutation) ⭐⭐ |
⚡ EXAM TRAP: NEET 2018, 2019
Hugo de Vries — mutations are random & directionless; saltation = single step large mutation.
⚡ EXAM TRAP: NEET 2012
Darwin = small, directional variations; de Vries = random, directionless mutations.
VI. HARDY–WEINBERG PRINCIPLE
A CORE CONCEPT
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| FEATURE | DETAIL |
|---|---|
| Principle | Allele frequencies in a population are stable & constant from generation to generation ⭐⭐ |
| Gene Pool | Total genes and their alleles in a population ⭐ |
| Genetic Equilibrium | Gene pool remains constant ⭐ |
| Sum total of allelic frequencies | = 1 (p + q = 1) ⭐ |
⚡ EXAM TRAP: RE-NEET 2026
In a diploid population at Hardy-Weinberg equilibrium, if the frequency of allele A is 0.1, the frequency of AA (p²) = 0.01.
B HARDY–WEINBERG EQUATION
🔑 EQUATION: p² + 2pq + q² = 1 (Binomial expansion of (p + q)²)
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| SYMBOL | REPRESENTS |
|---|---|
| p | Frequency of dominant allele (A) ⭐ |
| q | Frequency of recessive allele (a) ⭐ |
| p² | Frequency of homozygous dominant (AA) ⭐ |
| q² | Frequency of homozygous recessive (aa) ⭐ |
| 2pq | Frequency of heterozygous (Aa) ⭐ |
⚡ EXAM TRAP: NEET 2014, 2016, 2019
Hardy-Weinberg equation — p² + 2pq + q² = 1; know all components.
C DISTURBANCE IN EQUILIBRIUM = EVOLUTION
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| FEATURE | DETAIL |
|---|---|
| If measured frequency differs from expected | Indicates extent of evolutionary change ⭐ |
| Disturbance in H-W equilibrium | Interpreted as resulting in evolution ⭐ |
D FIVE FACTORS AFFECTING H-W EQUILIBRIUM
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| FACTOR | DETAIL |
|---|---|
| 1. Gene Migration / Gene Flow | Migration of section of population → gene frequencies change in both populations; if happens multiple times = Gene Flow ⭐⭐ |
| 2. Genetic Drift | Change in allele frequency by chance (operates in small, isolated populations) ⭐⭐ |
| 3. Mutation | New alleles arise ⭐ |
| 4. Genetic Recombination | During gametogenesis ⭐ |
| 5. Natural Selection | Heritable variations enabling better survival → more progeny ⭐ |
⚡ EXAM TRAP: NEET 2013, 2021, 2024, RE-NEET 2024
Five factors — Gene migration/flow, Genetic drift, Mutation, Genetic recombination, Natural selection.
🔑 NOTE: Random mating SUPPORTS equilibrium; Selective mating DISTURBS it.
E FOUNDER EFFECT
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| FEATURE | DETAIL |
|---|---|
| Definition | When allelic frequency is so different in a new sample of population → they become a different species ⭐ |
| The original drifted population | Becomes founders ⭐ |
| This phenomenon | Called Founder Effect ⭐ |
⚡ EXAM TRAP: NEET 2017, 2019, 2021, 2022
Founder Effect — small group leaves, forms new population with different gene frequency → becomes founders.
F TYPES OF NATURAL SELECTION
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| TYPE | DETAIL | GRAPH CHANGE | EXAMPLE |
|---|---|---|---|
| Stabilising | More individuals acquire mean character value ⭐ | Peak gets higher & narrower; eliminates extremes | Human birth weight (average weight babies survive best) ⭐ |
| Directional | More individuals acquire value other than the mean ⭐ | Peak shifts in one direction | Industrial Melanism; Artificial selection for high milk yield ⭐ |
| Disruptive | More individuals acquire peripheral character values (both ends) ⭐ | Two peaks form | — |
⚡ EXAM TRAP: NEET 2017, 2019, 2022
Three types of natural selection — Stabilising (mean), Directional (shift), Disruptive (both ends).
⚡ EXAM TRAP: RE-NEET 2026
Natural selection can lead to stabilisation, directional change and disruption — genetic drift is NOT an outcome of natural selection.
G HARDY–WEINBERG PYQ MATH
🔑 Example 1 (NEET 2019): Allele A = 0.4 (p); allele a = 0.6 (q) → AA (p²) = 0.16; Aa (2pq) = 2 × 0.4 × 0.6 = 0.48; aa (q²) = 0.36
🔑 Example 2 (NEET 2014): AA = 360, Aa = 480, aa = 160; Total = 1000 → Total alleles = 2000; A alleles = (360×2) + 480 = 1200; Frequency of A = 1200/2000 = 0.6
🔑 Example 3 (RE-NEET 2026): p = 0.1 → AA = p² = 0.01; aa = q² = (0.9)² = 0.81; Aa = 2pq = 2 × 0.1 × 0.9 = 0.18
VII. A BRIEF ACCOUNT OF EVOLUTION
A TIMELINE OF LIFE ON EARTH
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| TIME (MYA) | EVENT |
|---|---|
| ~2000 mya | First cellular forms of life appeared ⭐ |
| ~500 mya | Invertebrates formed & active ⭐ |
| ~350 mya | Jawless fish probably evolved ⭐ |
| ~350 mya | Fish with stout & strong fins could move on land & go back to water ⭐ |
| ~320 mya | Sea weeds & few plants existed ⭐ |
| ~200 mya | Reptiles of different shapes & sizes dominated on earth ⭐ |
| ~200 mya | Some land reptiles went back into water → fish-like reptiles (e.g., Ichthyosaurs) ⭐ |
| ~65 mya | Dinosaurs suddenly disappeared ⭐ |
⚡ EXAM TRAP: NEET 2024, RE-NEET 2024
Evolution timeline — know key dates (2000 mya first cells; 65 mya dinosaurs disappeared).
⚡ EXAM TRAP: NEET 2026
Match-the-list chronology: About 65 mya — dinosaurs suddenly disappeared; About 500 mya — invertebrates were formed and became active; About 350 mya — jawless fish probably evolved; About 320 mya — seaweeds and few plants probably existed.
B KEY EVOLUTIONARY EVENTS
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| FEATURE | DETAIL |
|---|---|
| First to invade land | Plants ⭐⭐ |
| Plants were widespread | When animals invaded land ⭐ |
| Lobefins / Coelacanth | Fish with stout fins → moved on land & back to water; ancestors of modern frogs & salamanders ⭐ |
| Coelacanth (1938) | Caught in South Africa; thought to be extinct ⭐ |
| Amphibians evolved into | Reptiles ⭐ |
| Reptile eggs | Thick-shelled (do not dry in sun, unlike amphibian eggs) ⭐ |
| Modern reptile descendants | Turtles, Tortoises, Crocodiles ⭐ |
| Giant ferns | Were present → all fell to form coal deposits ⭐ |
| Tyrannosaurus rex | Biggest reptile; ~20 feet in height; huge dagger-like teeth ⭐ |
| Dinosaur disappearance | ~65 mya; reason unclear (climate changes? evolved into birds?) ⭐ |
C EVOLUTION OF MAMMALS
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| FEATURE | DETAIL |
|---|---|
| First mammals | Like shrews (small-sized fossils) ⭐ |
| Characteristics | Viviparous; protected unborn young inside mother's body; more intelligent ⭐ |
| Continental drift impact | South America joined North America → SA mammals overridden by NA fauna ⭐ |
| Australian marsupials survived | Due to continental drift → lack of competition from other mammals ⭐ |
| Mammals in water | Whales, Dolphins, Seals, Sea cows ⭐ |
| Most successful story | Evolution of man with language skills & self-consciousness ⭐ |
⚡ EXAM TRAP: NEET 2012
Most successful story = evolution of man; language skills & self-consciousness.
D GEOLOGICAL ERAS
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| ERA | ALSO KNOWN AS | DOMINANT LIFE |
|---|---|---|
| Proterozoic | — | Lower invertebrates ⭐ |
| Palaeozoic | — | Fish & Amphibia ⭐ |
| Mesozoic | Age of Reptiles ⭐⭐ | Dinosaurs ⭐⭐ |
| Cenozoic | Age of Mammals ⭐⭐ | Mammals ⭐⭐ |
🔑 PERIOD ORDER: Silurian → Devonian → Carboniferous → Permian
⚡ EXAM TRAP: NEET 2024
Geological eras & periods — Mesozoic = Age of Reptiles; Cenozoic = Age of Mammals.
VIII. ORIGIN & EVOLUTION OF MAN
A TIMELINE OF HUMAN EVOLUTION
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| TIME | ORGANISM | KEY FEATURES |
|---|---|---|
| ~15 mya | Dryopithecus & Ramapithecus (Primates) | Hairy; walked like gorillas & chimps; Ramapithecus = more man-like; Dryopithecus = more ape-like ⭐⭐ |
| 3–4 mya | Man-like primates | Walked in Eastern Africa; not taller than 4 feet; walked upright ⭐ |
| ~2 mya | Australopithecus | Lived in East African grasslands; hunted with stone weapons; ate fruits ⭐ |
| — | Homo habilis | First human-like being (hominid); brain 650–800 cc; probably did NOT eat meat ⭐⭐⭐ |
| ~1.5 mya | Homo erectus | Fossils discovered in Java (1891); brain ~900 cc; probably ate meat ⭐⭐ |
| 1,00,000–40,000 ya | Neanderthal man | Brain 1400 cc; lived in near east & central Asia; used hides; buried their dead ⭐⭐⭐ |
| — | Homo sapiens | Arose in Africa; moved across continents; developed into distinct races ⭐ |
| 75,000–10,000 ya | Modern Homo sapiens | Arose during Ice Age ⭐ |
| ~18,000 ya | Pre-historic cave art | Developed ⭐ |
| ~10,000 ya | Agriculture began | Human settlements started ⭐ |
⚡ EXAM TRAP: NEET 2015, 2019
Homo habilis = 650–800 cc (smallest brain among Homo species).
⚡ EXAM TRAP: NEET 2019
Homo erectus = Java (1891); ~900 cc; probably ate meat.
⚡ EXAM TRAP: NEET 2012, 2016, 2019
Neanderthal = 1400 cc; near east/central Asia; used hides; buried their dead.
⚡ EXAM TRAP: RE-NEET 2026
Modern Homo sapiens arose in AFRICA (not Australia) and moved across continents; Homo sapiens arose around 75,000 to 10,000 years ago during the Ice Age.
B FOSSIL DISCOVERY LOCATIONS
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| FEATURE | DETAIL |
|---|---|
| Man-like bone fossils | Discovered in Ethiopia & Tanzania ⭐ |
| Homo erectus fossils | Discovered in Java (1891) ⭐ |
| Cave paintings | Bhimbetka rock shelter, Raisen district, Madhya Pradesh ⭐ |
C CRANIAL CAPACITIES — QUICK REFERENCE
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| SPECIES | BRAIN CAPACITY (CC) |
|---|---|
| Homo habilis | 650–800 cc ⭐ |
| Homo erectus | ~900 cc ⭐ |
| Neanderthal man | 1400 cc ⭐ |
| Homo sapiens | 1350–1400 cc ⭐ |
D SEQUENCE OF HUMAN EVOLUTION
🔑 SEQUENCE: Ramapithecus → Australopithecus → Homo habilis → Homo erectus → Neanderthal → Homo sapiens
⚡ EXAM TRAP: NEET 2016, 2024
Know the correct sequence of human evolution — Ramapithecus → Australopithecus → Homo habilis → Homo erectus → Neanderthal → Homo sapiens.
⚡ EXAM TRAP: NEET 2026
Evolution of man runs parallel to progressive development of brain and language skills; correct order of appearance = Ramapithecus → Homo habilis → Homo erectus → Neanderthal → Homo sapiens.
IX. RAPID REVISION — KEY COMPARISON TABLES
TABLE 1: Theories of Origin of Life ⭐⭐⭐
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| THEORY | PROPONENT | KEY IDEA |
|---|---|---|
| Special Creation | Religious literature | All species created; diversity constant; Earth ~4000 years |
| Spontaneous Generation | Ancient belief | Life from decaying matter |
| Biogenesis | Louis Pasteur | Life from pre-existing life only |
| Panspermia | Greek thinkers | Spores from space |
| Chemical Evolution | Oparin & Haldane | Non-living organic molecules → life |
TABLE 2: Homologous vs Analogous Organs ⭐⭐⭐
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| FEATURE | HOMOLOGOUS | ANALOGOUS |
|---|---|---|
| Anatomical structure | Same | Different |
| Function | Different | Same |
| Ancestry | Common | Different |
| Evolution type | Divergent | Convergent |
| Examples (Animals) | Forelimbs of whale, bat, cheetah, human | Flippers of penguins & dolphins; Eye of octopus & mammals |
| Examples (Plants) | Thorn of Bougainvillea & Tendril of Cucurbita | Sweet potato & Potato |
TABLE 3: Darwin vs Hugo de Vries ⭐⭐⭐
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| FEATURE | DARWIN | HUGO DE VRIES |
|---|---|---|
| Organism | Various | Evening Primrose |
| Variations | Small, Directional | Random, Directionless (Mutations) |
| Evolution speed | Gradual | Jerky (Saltation) |
| Speciation cause | Natural Selection | Mutations |
TABLE 4: Types of Natural Selection ⭐⭐⭐
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| TYPE | CHARACTER SELECTED | GRAPH CHANGE | EXAMPLE |
|---|---|---|---|
| Stabilising | Mean value | Peak higher & narrower | Human birth weight |
| Directional | Other than mean | Peak shifts one direction | Industrial Melanism |
| Disruptive | Peripheral (both ends) | Two peaks form | — |
TABLE 5: Hardy–Weinberg Equation Components ⭐⭐⭐
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| SYMBOL | MEANING |
|---|---|
| p | Dominant allele frequency |
| q | Recessive allele frequency |
| p² | Homozygous dominant (AA) |
| q² | Homozygous recessive (aa) |
| 2pq | Heterozygous (Aa) |
| p + q | = 1 |
| p² + 2pq + q² | = 1 |
TABLE 6: Five Factors Disturbing H-W Equilibrium ⭐⭐⭐
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| FACTOR | DETAIL |
|---|---|
| Gene Migration / Gene Flow | Migration → gene frequency changes; multiple times = gene flow |
| Genetic Drift | Chance change in allele frequency; small populations (NOT an outcome of natural selection) |
| Mutation | New alleles arise |
| Genetic Recombination | During gametogenesis |
| Natural Selection | Better adapted → more progeny |
TABLE 7: Placental Mammals vs Australian Marsupials ⭐⭐⭐
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| PLACENTAL MAMMAL | AUSTRALIAN MARSUPIAL |
|---|---|
| Mole | Marsupial mole |
| Anteater | Numbat |
| Mouse | Marsupial mouse |
| Lemur | Spotted Cuscus |
| Flying Squirrel | Flying Phalanger |
| Bobcat | Tasmanian Tiger Cat |
| Wolf | Tasmanian Wolf |
TABLE 8: Human Evolution — Quick Reference ⭐⭐⭐
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| SPECIES | TIME | BRAIN (CC) | KEY FEATURES |
|---|---|---|---|
| Dryopithecus | 15 mya | — | Ape-like |
| Ramapithecus | 15 mya | — | Man-like |
| Australopithecus | 2 mya | — | Stone weapons; ate fruit; East Africa |
| Homo habilis | — | 650–800 | First hominid; did not eat meat |
| Homo erectus | 1.5 mya | ~900 | Java (1891); ate meat |
| Neanderthal | 1,00,000–40,000 ya | 1400 | Near east/Central Asia; hides; buried dead |
| Homo sapiens | — | 1350–1400 | Africa origin; distinct races |
TABLE 9: Geological Eras ⭐⭐⭐
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| ERA | DOMINANT LIFE |
|---|---|
| Proterozoic | Lower invertebrates |
| Palaeozoic | Fish & Amphibia |
| Mesozoic | Reptiles (Dinosaurs) |
| Cenozoic | Mammals |
TABLE 10: Timeline of Life on Earth ⭐⭐⭐
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| TIME | EVENT |
|---|---|
| ~13.8 billion ya | Origin of universe (Big Bang) |
| ~4.5 billion ya | Origin of Earth |
| ~4 billion ya | Origin of life |
| ~3 billion ya | First non-cellular forms |
| ~2000 mya | First cellular forms |
| ~500 mya | Invertebrates formed & active |
| ~350 mya | Jawless fish; lobefins |
| ~320 mya | Sea weeds & few plants |
| ~200 mya | Reptiles dominated; Ichthyosaurs |
| ~65 mya | Dinosaurs disappeared |
| ~15 mya | Dryopithecus & Ramapithecus |
| ~3–4 mya | Man-like primates (Eastern Africa) |
| ~2 mya | Australopithecus |
| ~1.5 mya | Homo erectus |
| 1,00,000–40,000 ya | Neanderthal man |
| 75,000–10,000 ya | Modern Homo sapiens (Ice Age) |
| ~18,000 ya | Pre-historic cave art |
| ~10,000 ya | Agriculture began |
TABLE 11: Key Numbers — Quick Reference ⭐⭐⭐
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| PARAMETER | VALUE |
|---|---|
| Universe age | ~13.8 billion years |
| Earth age | ~4.5 billion years |
| Life origin | ~4 billion years ago |
| First cellular forms | ~2000 mya |
| Special Creation Earth age claim | ~4000 years |
| Miller's temperature | 800°C |
| Miller's gases | CH₄, H₂, NH₃, H₂O vapour |
| Miller's product | Amino acids |
| First land organisms | Plants |
| Dinosaur disappearance | ~65 mya |
| T. rex height | ~20 feet |
| Homo habilis brain | 650–800 cc |
| Homo erectus brain | ~900 cc |
| Neanderthal brain | 1400 cc |
| Homo sapiens brain | 1350–1400 cc |
| H. erectus fossils | Java (1891) |
| Pre-historic cave art | ~18,000 ya |
| Agriculture | ~10,000 ya |
| Cave paintings (India) | Bhimbetka, Raisen, MP |
X. COMMON EXAM TRAPS — QUICK REFERENCE
CONSOLIDATED PYQ Q&A TABLE ⭐⭐⭐
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| TRAP / QUESTION | CORRECT ANSWER |
|---|---|
| Evolutionary Biology is? | Study of history of life forms on earth ⭐ |
| Stellar distances measured in? | Light years ⭐ |
| Universe age? | ~13.8 billion years (some say ~20 billion) ⭐ |
| Big Bang Theory explains? | Origin of universe ⭐ |
| Earth age? | ~4.5 billion years ⭐ |
| Life origin? | ~4 billion years ago (500 my after Earth formed) ⭐ |
| Theory of Panspermia? | Spores transferred to planets including Earth ⭐ |
| Spontaneous generation? | Life from decaying matter (straw, mud) ⭐ |
| Who dismissed spontaneous generation? | Louis Pasteur (pre-sterilised flasks) ⭐⭐ |
| Did Pasteur explain first life? | NO — only showed life from pre-existing life ⭐ |
| Chemical evolution proposed by? | Oparin (Russia) & Haldane (England) ⭐⭐ |
| First form of life from? | Pre-existing non-living organic molecules ⭐ |
| Early Earth atmosphere type? | Reducing (CH₄, NH₃, water vapour) ⭐ |
| Miller's experiment — gases? | CH₄, H₂, NH₃, water vapour ⭐⭐ |
| Miller's temperature? | 800°C ⭐ |
| Miller's energy source? | Electric discharge ⭐ |
| Miller's product? | Amino acids ⭐⭐ |
| Sequence of chemical evolution? | Monomers → Polymers → Protobionts → DNA systems ⭐⭐ |
| First organisms were? | Non-green, presumably anaerobes ⭐ |
| First autotrophs? | Chemoautotrophs ⭐ |
| First cellular forms? | ~2000 mya ⭐ |
| Special Creation — Earth age? | ~4000 years ⭐ |
| Darwin's ship? | H.M.S. Beagle ⭐ |
| Darwin's key concepts? | (1) Branching descent (2) Natural selection ⭐⭐ |
| Fitness according to Darwin? | Reproductive fitness ⭐⭐ |
| Natural selection means? | Better fit → more progeny → selected by nature ⭐ |
| Alfred Wallace worked in? | Malay Archipelago ⭐ |
| Lamarck's theory? | Use and disuse of organs (e.g., giraffe neck) ⭐ |
| Is Lamarck's theory accepted today? | NO ⭐ |
| Thomas Malthus influenced? | Darwin (work on populations) ⭐ |
| Evolution is a directed process? | NO — it is stochastic (chance-based) ⭐⭐ |
| Fossils are? | Remains of hard parts of life-forms in rocks ⭐ |
| Study of fossils? | Palaeontology ⭐ |
| Embryological evidence proposed by? | Ernst Haeckel ⭐ |
| Disapproved by? | Karl Ernst von Baer ⭐⭐⭐ |
| Haeckel's embryological support? | Disapproved by Karl Ernst von Baer — no longer valid evidence ⭐⭐⭐ |
| Von Baer's observation? | Embryos never pass through adult stages of other animals ⭐ |
| Homologous organs? | Same structure, different function, common ancestry ⭐⭐ |
| Analogous organs? | Different structure, same function, different ancestry ⭐⭐ |
| Divergent evolution → ? | Homologous organs ⭐ |
| Convergent evolution → ? | Analogous organs ⭐ |
| Is convergent evolution an evidence of common ancestry? | No ⭐⭐⭐ |
| Forelimbs of humans and bats? | Homologous — similar anatomical structure ⭐⭐⭐ |
| Forelimbs of whales and bats? | Divergent evolution (not convergent) ⭐⭐⭐ |
| Bones in mammalian forelimbs? | Humerus, radius, ulna, carpals, metacarpals, phalanges ⭐ |
| Thorn (Bougainvillea) & Tendril (Cucurbita) = ? | Homologous ⭐⭐ |
| Eyes of octopuses and mammals? | Convergent evolution / Analogous ⭐⭐ |
| Wings of butterflies and birds? | Convergent evolution ⭐⭐ |
| Flippers of penguins and dolphins? | Convergent evolution ⭐⭐⭐ |
| Sweet potato and potato? | Analogy, convergent evolution (root vs stem) ⭐⭐⭐ |
| Placental mammals ↔ Australian marsupials similarity? | Convergent evolution ⭐⭐⭐ |
| Industrial Melanism from? | England ⭐ |
| Before industrialisation (1850s)? | More white-winged moths ⭐ |
| After industrialisation (1920)? | More dark-winged (melanised) moths ⭐ |
| Why dark moths survived after industrialisation? | Camouflaged against dark (sooty) tree trunks ⭐ |
| Lichens = ? | Pollution indicators (don't grow in polluted areas) ⭐⭐ |
| Rural areas — melanic moth count? | Low ⭐ |
| Type of natural selection in Industrial Melanism? | Directional ⭐⭐ |
| Anthropogenic action examples? | Herbicide/antibiotic resistance; breeds of dogs ⭐ |
| Adaptive radiation definition? | Different species evolving from a point, radiating to other areas ⭐⭐ |
| Darwin's Finches — location? | Galapagos Islands ⭐⭐ |
| Darwin's Finches — original diet? | Seed-eating ⭐ |
| Finches evolved into? | Insectivorous & vegetarian forms ⭐ |
| Australian Marsupials example of? | Adaptive radiation ⭐ |
| Why Australian marsupials survived? | Lack of competition (continental drift) ⭐ |
| Placental Wolf corresponds to? | Tasmanian Wolf ⭐⭐ |
| Flying Squirrel corresponds to? | Flying Phalanger ⭐ |
| Lemur corresponds to? | Spotted Cuscus ⭐ |
| Hugo de Vries worked on? | Evening Primrose (Oenothera lamarckiana) ⭐ |
| Darwin's variations? | Small & directional ⭐ |
| de Vries' mutations? | Random & directionless ⭐⭐ |
| Saltation? | Single step large mutation (de Vries) ⭐⭐ |
| Hardy-Weinberg equation? | p² + 2pq + q² = 1 ⭐⭐ |
| p + q = ? | 1 ⭐ |
| p² = ? | Homozygous dominant (AA) ⭐ |
| q² = ? | Homozygous recessive (aa) ⭐ |
| 2pq = ? | Heterozygous (Aa) ⭐ |
| If frequency of allele A = 0.1, frequency of AA? | 0.01 (p²) ⭐⭐⭐ |
| Gene Pool? | Total genes & alleles in a population ⭐ |
| Genetic Equilibrium? | Gene pool remains constant ⭐ |
| Disturbance in H-W equilibrium = ? | Evolution ⭐ |
| Five factors affecting H-W? | Gene migration/flow, Genetic drift, Mutation, Genetic recombination, Natural selection ⭐⭐ |
| Gene flow? | Gene migration happening multiple times ⭐ |
| Genetic drift? | Chance change; small populations ⭐ |
| Is genetic drift an outcome of natural selection? | No ⭐⭐⭐ |
| Natural selection can lead to? | Stabilisation, directional change, disruption ⭐⭐⭐ |
| Founder Effect? | Drifted population with different allele frequency → different species; original = founders ⭐⭐ |
| Random mating — effect on H-W? | Supports equilibrium ⭐ |
| Selective mating — effect? | Disturbs equilibrium ⭐ |
| Stabilising selects for? | Mean character value ⭐ |
| Directional selects for? | Value other than mean ⭐ |
| Disruptive selects for? | Peripheral values (both ends) ⭐ |
| Example of Stabilising? | Human birth weight (average survives best) ⭐ |
| Example of Directional? | Industrial Melanism; artificial selection (milk yield) ⭐ |
| First land organisms? | Plants ⭐⭐ |
| Coelacanth caught where/when? | South Africa, 1938 ⭐ |
| Lobefins are ancestors of? | Modern frogs & salamanders ⭐ |
| Amphibians evolved into? | Reptiles ⭐ |
| Reptile egg feature? | Thick-shelled (don't dry in sun) ⭐ |
| Giant ferns formed? | Coal deposits ⭐ |
| Ichthyosaurs? | Land reptiles that went back to water (~200 mya) ⭐ |
| T. rex? | Biggest reptile; ~20 feet; dagger-like teeth ⭐ |
| About 65 mya? | Dinosaurs suddenly disappeared ⭐⭐ |
| About 500 mya? | Invertebrates formed and became active ⭐⭐ |
| About 350 mya? | Jawless fish probably evolved ⭐⭐ |
| About 320 mya? | Seaweeds and few plants existed ⭐⭐ |
| First mammals like? | Shrews (small-sized) ⭐ |
| Mammals wholly in water? | Whales, Dolphins, Seals, Sea cows ⭐ |
| Dryopithecus was? | More ape-like ⭐ |
| Ramapithecus was? | More man-like ⭐ |
| Primates existed? | ~15 mya ⭐ |
| Man-like fossils found in? | Ethiopia & Tanzania ⭐ |
| Man-like primates walked in? | Eastern Africa (~3–4 mya) ⭐ |
| Australopithecus lived where/when? | East African grasslands; ~2 mya ⭐ |
| Australopithecus diet? | Hunted with stone weapons; ate fruit ⭐ |
| Homo habilis brain? | 650–800 cc ⭐⭐ |
| Homo habilis diet? | Probably did NOT eat meat ⭐ |
| First human-like being? | Homo habilis ⭐⭐ |
| Homo erectus fossils? | Java (1891) ⭐ |
| Homo erectus brain? | ~900 cc ⭐ |
| Homo erectus diet? | Probably ate meat ⭐ |
| Neanderthal brain? | 1400 cc ⭐⭐ |
| Neanderthal region? | Near east & central Asia ⭐ |
| Neanderthal time? | 1,00,000–40,000 years ago ⭐ |
| Neanderthal features? | Used hides; buried their dead ⭐⭐ |
| Modern Homo sapiens arose in? | Africa ⭐⭐⭐ |
| Homo sapiens arose around? | 75,000 to 10,000 years ago (Ice Age) ⭐⭐ |
| Cave art? | ~18,000 ya ⭐ |
| Bhimbetka cave paintings? | Raisen district, Madhya Pradesh ⭐ |
| Agriculture? | ~10,000 ya ⭐ |
| Sequence of human evolution? | Ramapithecus → Australopithecus → H. habilis → H. erectus → Neanderthal → H. sapiens ⭐⭐⭐ |
| Proterozoic Era? | Lower invertebrates ⭐ |
| Palaeozoic Era? | Fish & Amphibia ⭐ |
| Mesozoic Era? | Age of Reptiles (Dinosaurs) ⭐⭐ |
| Cenozoic Era? | Age of Mammals ⭐⭐ |
| Period order? | Silurian → Devonian → Carboniferous → Permian ⭐ |
| Geological history closely correlates with? | Biological history of earth ⭐ |
| Most successful evolution story? | Evolution of man (language skills & self-consciousness) ⭐ |