# Evolution (NEET Biology Class 12): Hardy-Weinberg, Homologous vs Analogous & Human Origins Source: https://tracknation.in/story/evolution-neet-biology-class-12-hardy-weinberg-homologous-vs-analogous-human-origins (TrackNation β€” free UPSC notes with PYQs) > NEET Class 12 Evolution, mined from NCERT: origin-of-life theories in a table (panspermia, spontaneous generation and Pasteur, Oparin-Haldane), the Miller experiment with exact conditions, an evidence-for-evolution table (fossils, homologous vs analogous organs with all examples, embryology), industrial melanism worked through, adaptive radiation, a Lamarck-vs-Darwin comparison plus de Vries, the full Hardy-Weinberg principle with the equation and all five disturbing factors tabulated, the three ## Origin of Life & Evidence for Evolution 🎯 **NEET priority: High-yield.** *3–5 questions every year. The **Hardy-Weinberg equation and its five disturbing factors**, **homologous vs analogous organs**, and the **human evolution timeline with brain sizes** are the three near-guaranteed scorers.* ### Origin of life β€” the competing ideas | **Theory / Scientist** | **What it claimed** | **Status** | | Panspermia | Spores (units of life) were transferred to earth from outer space β€” an early Greek idea | Still a favourite for some astronomers | | Spontaneous generation | Life arose from decaying matter like straw and mud | DISMISSED β€” Louis Pasteur showed life comes only from PRE-EXISTING life (pre-sterilised flasks grew nothing; flasks open to air did) | | Theory of special creation | All species were created as-is, diversity never changed, earth is ~4000 years old | Rejected | | Oparin (Russia) and Haldane (England) | The first life came from pre-existing NON-LIVING organic molecules; CHEMICAL EVOLUTION preceded biological evolution | Broadly accepted | ### The Miller-Urey experiment (1953) - **S.L. Miller** recreated early-earth conditions in a closed flask: **CHβ‚„, Hβ‚‚, NH₃ and water vapour at 800Β°C**, with **electric discharge** simulating lightning. He observed the formation of **amino acids**. Similar experiments produced **sugars, nitrogen bases, pigments and fats**. Analysis of **meteorite content** revealed the same compounds β€” suggesting the process occurs elsewhere in space too. - **Timeline:** the first **non-cellular** forms of life could have arisen about **3 billion years** ago (giant molecules β€” RNA, protein, polysaccharides). The first **cellular** forms did not appear until about **2000 million years** ago, all in a **water environment**. ### Evidence for evolution | **Evidence** | **What it shows** | **Example** | | Palaeontology (fossils) | Fossils in different SEDIMENTARY LAYERS indicate the geological period they existed in β€” life forms have changed over time | Fossils dated by radioactive methods | | Homologous organs β†’ DIVERGENT evolution | SAME structure, DIFFERENT functions β€” indicating common ancestry | Forelimbs of whales, bats, cheetah and humans: same bone pattern (humerus, radius, ulna, carpals, metacarpals, phalanges), different uses. In plants: thorn and tendril of Bougainvillea and Cucurbita | | Analogous organs β†’ CONVERGENT evolution | DIFFERENT structure, SAME function β€” different ancestries converging on the same solution | Wings of butterfly and bird; eyes of octopus and mammal; flippers of penguins and dolphins; sweet potato (root modification) and potato (stem modification) | | Comparative biochemistry | Similarities in proteins and genes among diverse organisms | β€” | | Embryology | Embryos of all vertebrates develop a row of vestigial gill slits | β€” | ## Industrial Melanism, Adaptive Radiation & the Theories ### Industrial melanism β€” evolution observed in real time - **Before industrialisation:** tree trunks were covered with thick, almost-white **lichen**. The **white-winged moth survived** (camouflaged); dark moths were picked off by predators. - **After industrialisation:** smoke and soot **darkened the tree trunks**. Now the **dark/melanised moth survived** and the white-winged moth was eaten. - The clinching evidence: in **rural areas where industrialisation did NOT occur**, the count of melanic moths stayed **low**. Note also that **lichens are industrial pollution indicators** β€” they will not grow in polluted areas. Crucially, **no variant is completely wiped out**. - The same logic explains **pesticide/herbicide resistance** and **antibiotic resistance** β€” appearing over **months or years, not centuries**. These are examples of **evolution by anthropogenic action**, and they show evolution is **NOT a directed/deterministic process** β€” it is a **STOCHASTIC process based on chance events**. ### Adaptive radiation - Darwin observed **Darwin's Finches** on the **Galapagos Islands** β€” many varieties on the same island, all evolved from a **seed-eating ancestral** stock into **insectivorous and vegetarian** forms with altered beaks. Evolution of different species in a geographical area starting from a point and radiating out is **adaptive radiation**. - **Australian marsupials** are the other classic example. When **more than one adaptive radiation** occurs in an isolated geographical area (representing different habitats), that is **convergent evolution** β€” e.g. Australian marsupials and placental mammals. ### Lamarck vs Darwin | **Aspect** | **Lamarck** | **Darwin** | | Driver of evolution | USE and DISUSE of organs | NATURAL SELECTION | | Classic example | Giraffes stretched their necks to reach tall leaves and passed the elongated neck on to offspring | Heritable variations that improve resource utilisation let those individuals reproduce more | | Status | 'Nobody believes this conjecture any more' β€” acquired characters are not inherited | Accepted, and influenced by Thomas Malthus's work on populations | Darwin's observations were factual: **natural resources are limited**; **populations are stable in size** except for seasonal fluctuation; members of a population **vary** (no two individuals are alike); **most variations are inherited**. Since populations would grow exponentially if all reproduced maximally, yet real populations are limited, there must be **competition for resources**. **Alfred Wallace** arrived at the same conclusion independently. **Hugo de Vries** proposed **mutation** as the driver, from work on evening primrose β€” but his mutations were **random and directionless**, causing evolution in a **single step (saltation)**, whereas **Darwinian variations are small and directional** and evolution is **gradual**. ## Hardy-Weinberg Principle & Natural Selection ### Hardy-Weinberg principle β€” the equation NEET asks every year - Allele frequencies in a population are **stable and constant from generation to generation** β€” the **gene pool** (total genes and alleles in a population) remains constant. This is **genetic equilibrium**, and the **sum of all allelic frequencies is 1**. - For a diploid with alleles A (frequency **p**) and a (frequency **q**): frequency of **AA = pΒ²**, **aa = qΒ²**, **Aa = 2pq**. So **pΒ² + 2pq + qΒ² = 1** β€” the binomial expansion of **(p + q)Β²**. - **When measured frequency DIFFERS from the expected value, that difference measures the extent of evolutionary change.** Disturbance of Hardy-Weinberg equilibrium IS evolution. | **The 5 factors that disturb Hardy-Weinberg equilibrium** | **What it does** | | Gene migration / gene flow | Migration changes gene frequencies in BOTH the original and the new population β€” new alleles are added to one and lost from the other. Repeated migration = gene flow | | Genetic drift | The SAME change occurring BY CHANCE. If the drifted population's allele frequency differs so much they become a different species, the originals are FOUNDERS and the effect is the FOUNDER EFFECT | | Mutation | Pre-existing advantageous mutations, when selected, produce new phenotypes β€” over generations this leads to SPECIATION | | Genetic recombination | Variation generated during gametogenesis | | Natural selection | Heritable variations enabling better survival leave greater numbers of progeny | ### Three types of natural selection | **Type** | **What happens to the population** | | Stabilising | MORE individuals acquire the MEAN character value β€” variation is reduced | | Directional | More individuals acquire a value OTHER than the mean β€” the curve shifts one way | | Disruptive | More individuals acquire PERIPHERAL values at BOTH ends of the distribution curve | ## The Timeline of Evolution, Human Origins & Why This Matters for NEET ### A brief account of evolution β€” the timeline | **Time** | **What appeared** | | 2000 mya | First CELLULAR forms of life; some could release Oβ‚‚ | | 500 mya | Invertebrates formed and active | | 350 mya | Jawless fish evolved. Also, fish with stout strong fins could move onto land β€” the LOBEFINS. In 1938 a COELACANTH, thought extinct, was caught in South Africa | | 320 mya | Sea weeds and a few plants existed. PLANTS were the first organisms to invade land | | ~300–200 mya | Lobefins β†’ first AMPHIBIANS (ancestors of modern frogs and salamanders) β†’ REPTILES, which lay thick-shelled eggs that don't dry out | | 200 mya | Some land reptiles returned to water as fish-like reptiles (e.g. Ichthyosaurs). Land reptiles were the DINOSAURS β€” Tyrannosaurus rex stood about 20 feet with dagger-like teeth | | 65 mya | DINOSAURS suddenly disappeared. Cause unknown β€” possibly climatic change, possibly most evolved into birds | | After 65 mya | First MAMMALS were shrew-like; viviparous and more intelligent. Australian POUCHED mammals survived due to continental drift and lack of competition | ### Origin and evolution of man | **Form** | **When** | **Key features** | | Dryopithecus and Ramapithecus | ~15 mya | Hairy, walked like gorillas and chimpanzees. RAMAPITHECUS was more MAN-like; DRYOPITHECUS more APE-like | | Man-like primates (fossils in Ethiopia and Tanzania) | 3–4 mya | Walked UPRIGHT but were not taller than 4 feet | | Homo erectus | ~1.5 mya (brain ~900 cc) | Probably ate MEAT | | Neanderthal man | 1,00,000–40,000 years ago | Brain size 1400 cc. Lived in near east and central Asia; used HIDES to protect the body and BURIED their dead | | Homo sapiens | Arose in AFRICA, moved across continents | Developed into distinct races. Modern Homo sapiens arose during the ice age, 75,000–10,000 years ago | | Pre-historic cave art | ~18,000 years ago | Seen at the BHIMBETKA rock shelter, Raisen district, Madhya Pradesh | | Agriculture | ~10,000 years ago | Human settlements began | ### Why this matters for NEET - High-value one-liners: **Miller (1953)** used CHβ‚„, Hβ‚‚, NH₃ + water vapour at **800Β°C** and got **amino acids**; **Pasteur** disproved spontaneous generation; homologous = **divergent**, analogous = **convergent**; Hardy-Weinberg = **pΒ² + 2pq + qΒ² = 1** with **5** disturbing factors; Neanderthal brain = **1400 cc**; dinosaurs vanished **65 mya**; cave art at **Bhimbetka**. - **Trap:** **homologous organs share structure but differ in function** (divergent evolution from a common ancestor) β€” **analogous organs share function but differ in structure** (convergent). Students invert this constantly. Also, **sweet potato is a ROOT modification while potato is a STEM modification** β€” making them analogous, not homologous. And **de Vries' mutations were random and produced single-step saltation**, unlike Darwin's small, directional, gradual variations. ## Test Yourself: MCQs, PYQs & Active Recall Answer these, then close the article and do an Active Recall. Reveal each answer only after you commit to one. ## Practice Questions **Q1.** The theory of spontaneous generation was finally disproved by: - (a) Louis Pasteur - (b) Oparin - (c) Haldane - (d) S.L. Miller **Answer: (a)** β€” Pasteur showed that in pre-sterilised flasks no life appeared, while flasks open to air developed living organisms β€” life comes only from pre-existing life. **Q2.** Oparin and Haldane proposed that the first form of life arose from: - (a) Decaying matter - (b) Pre-existing non-living organic molecules - (c) Spores from outer space - (d) Special creation **Answer: (b)** β€” Oparin and Haldane proposed that life came from pre-existing non-living organic molecules, preceded by chemical evolution. **Q3.** In Miller's 1953 experiment, the gases used in the closed flask were: - (a) Only methane - (b) O2, N2 and CO2 - (c) CO2 and water only - (d) CH4, H2, NH3 and water vapour **Answer: (d)** β€” Miller created electric discharge in a flask containing CH4, H2, NH3 and water vapour at 800 degrees Celsius, obtaining amino acids. **Q4.** The forelimbs of whales, bats, cheetah and humans are an example of: - (a) Vestigial organs - (b) Homologous organs showing divergent evolution - (c) Adaptive radiation - (d) Analogous organs showing convergent evolution **Answer: (b)** β€” Same anatomical structure performing different functions indicates common ancestry β€” homologous organs, divergent evolution. **Q5.** The wings of a butterfly and a bird are: - (a) Analogous, showing convergent evolution - (b) Homologous, showing divergent evolution - (c) Vestigial structures - (d) Both homologous and analogous **Answer: (a)** β€” Different structures performing a similar function are analogous organs, the result of convergent evolution. **Q6.** During post-industrialisation, the moth that survived better was: - (a) Both equally - (b) The dark-winged or melanised moth - (c) Neither survived - (d) The white-winged moth **Answer: (b)** β€” Soot darkened the tree trunks, so the melanised moth was camouflaged while the white-winged moth was spotted by predators. **Q7.** Lichens are useful as: - (a) A source of antibiotics - (b) Food for moths - (c) Industrial pollution indicators - (d) Fossil markers **Answer: (c)** β€” Lichens will not grow in polluted areas, making them reliable indicators of industrial pollution. **Q8.** Darwin's Finches on the Galapagos Islands are the classic example of: - (a) Genetic drift - (b) Adaptive radiation - (c) Convergent evolution - (d) Industrial melanism **Answer: (b)** β€” Many finch varieties evolved from a seed-eating ancestral stock into insectivorous and vegetarian forms β€” adaptive radiation. **Q9.** Lamarck's theory of evolution was based on: - (a) Use and disuse of organs - (b) Random mutation - (c) Genetic drift - (d) Natural selection **Answer: (a)** β€” Lamarck proposed that evolution was driven by use and disuse of organs, with acquired characters inherited β€” an idea no longer accepted. **Q10.** Darwin's work on natural selection was influenced by the population studies of: - (a) Gregor Mendel - (b) Hugo de Vries - (c) Alfred Wallace - (d) Thomas Malthus **Answer: (d)** β€” Thomas Malthus's work on populations influenced Darwin's thinking about limited resources and competition. **Q11.** Hugo de Vries' mutations differed from Darwinian variations in that mutations are: - (a) Never inherited - (b) Small and directional - (c) Always beneficial - (d) Random and directionless, causing single-step change **Answer: (d)** β€” De Vries' mutations are random and directionless causing saltation (single-step evolution); Darwinian variations are small, directional and gradual. **Q12.** In the Hardy-Weinberg equation, the frequency of heterozygous individuals is represented by: - (a) 2pq - (b) p2 - (c) p + q - (d) q2 **Answer: (a)** β€” AA = p2, aa = q2 and Aa = 2pq, so p2 + 2pq + q2 = 1 β€” the binomial expansion of (p+q)2. **Q13.** How many factors are known to affect Hardy-Weinberg equilibrium? - (a) Four - (b) Seven - (c) Three - (d) Five **Answer: (d)** β€” Five factors: gene migration/gene flow, genetic drift, mutation, genetic recombination and natural selection. **Q14.** When a drifted population's allele frequency differs so much that they become a different species, the original individuals are called: - (a) Hybrids - (b) Migrants - (c) Founders - (d) Mutants **Answer: (c)** β€” The original drifted population becomes the founders, and the phenomenon is called the founder effect. **Q15.** In disruptive natural selection: - (a) More individuals acquire peripheral values at BOTH ends of the curve - (b) The curve shifts in one direction - (c) No change occurs - (d) More individuals acquire the mean character value **Answer: (a)** β€” Disruptive selection favours peripheral character values at both ends of the distribution curve. **Q16.** Dinosaurs disappeared from the earth approximately: - (a) 15 mya - (b) 200 mya - (c) 65 mya - (d) 2 mya **Answer: (c)** β€” About 65 million years ago dinosaurs suddenly disappeared; the true reason remains unknown. **Q17.** Which primate was more man-like? - (a) Neither - (b) Dryopithecus - (c) Both equally - (d) Ramapithecus **Answer: (d)** β€” Ramapithecus was more man-like while Dryopithecus was more ape-like; both existed about 15 mya. **Q18.** The brain size of Neanderthal man was approximately: - (a) 1400 cc - (b) 1200 cc - (c) 1650 cc - (d) 900 cc **Answer: (a)** β€” Neanderthal man had a brain size of 1400 cc and lived between 1,00,000 and 40,000 years ago. ### NEET Previous Year Questions (PYQs) *Real NEET previous-year questions on this chapter, with explanations in our own words.* **Q19.** Analogous organs are the result of: (NEET PYQ) - (a) Adaptive radiation - (b) Genetic drift - (c) Convergent evolution - (d) Divergent evolution **Answer: (c)** β€” Analogous organs have different structures but perform similar functions β€” the result of convergent evolution. **Q20.** Sweet potato and potato are an example of: (NEET PYQ) - (a) Homologous organs - (b) Vestigial organs - (c) Fossils - (d) Analogous organs **Answer: (d)** β€” Sweet potato is a modified ROOT and potato a modified STEM β€” different structures with a similar storage function, hence analogous. **Q21.** The Hardy-Weinberg principle states that allele frequencies in a population: (NEET PYQ) - (a) Depend only on mutation - (b) Always increase - (c) Change every generation - (d) Remain stable and constant from generation to generation **Answer: (d)** β€” Allele frequencies are stable and constant across generations β€” genetic equilibrium β€” and disturbance of this equilibrium is evolution. **Q22.** Pre-historic cave paintings by humans in India can be seen at: (NEET PYQ) - (a) Ajanta caves - (b) Ellora caves - (c) Elephanta caves - (d) Bhimbetka rock shelter, Madhya Pradesh **Answer: (d)** β€” Cave art developed about 18,000 years ago; one such site is the Bhimbetka rock shelter in Raisen district, Madhya Pradesh. **Q23.** The fish caught in South Africa in 1938, previously thought to be extinct, was a: (NEET PYQ) - (a) Lungfish - (b) Ichthyosaur - (c) Coelacanth - (d) Shark **Answer: (c)** β€” A Coelacanth β€” a lobefin thought extinct β€” was caught in South Africa in 1938; lobefins evolved into the first amphibians. **Q24.** Antibiotic resistance in bacteria illustrates that evolution is: (NEET PYQ) - (a) A stochastic process based on chance events - (b) Driven by use and disuse - (c) Impossible to observe - (d) A directed, deterministic process **Answer: (a)** β€” Resistant organisms appear in months or years, showing evolution is stochastic and based on chance events β€” not directed. **Q25.** The first organisms to invade land were: (NEET PYQ) - (a) Reptiles - (b) Plants - (c) Amphibians - (d) Insects **Answer: (b)** β€” NCERT states that plants were the first organisms to invade land, and were widespread when animals followed. **Q26.** Australian marsupials and placental mammals represent: (NEET PYQ) - (a) Genetic drift - (b) The founder effect - (c) Convergent evolution - (d) Divergent evolution only **Answer: (c)** β€” When more than one adaptive radiation occurs in an isolated area representing different habitats, it is called convergent evolution. **Q27.** The first cellular forms of life appeared approximately: (NEET PYQ) - (a) 3 billion years ago - (b) 2000 million years ago - (c) 65 mya - (d) 500 mya **Answer: (b)** β€” Non-cellular forms may date to 3 billion years ago, but the first CELLULAR forms did not appear until about 2000 million years ago. **Q28.** In stabilising natural selection: (NEET PYQ) - (a) More individuals acquire the mean character value - (b) Variation increases - (c) Peripheral values are favoured at both ends - (d) The curve shifts one way **Answer: (a)** β€” Stabilising selection favours the mean character value, reducing variation in the population. ### Active Recall Prompt Write everything you can recall about **Evolution**, naming each part first: the **origin of life** (panspermia, spontaneous generation and Pasteur, Oparin-Haldane, the Miller experiment and its exact conditions); the **evidence for evolution** (fossils, homologous vs analogous organs with examples, embryology); **industrial melanism** and evolution by anthropogenic action; **adaptive radiation** (Darwin's finches, Australian marsupials); **Lamarck vs Darwin vs de Vries**; the **Hardy-Weinberg principle** (the full equation and all five disturbing factors); the **three types of natural selection**; the **timeline of evolution**; and the **origin and evolution of man** with each form and its features. Begin each fact with its topic and end it with a full stop.