NEET Evolution Previous Year Questions with Solutions

Based on which phenotypes are favored relative to environmental pressures, natural selection on continuous polygenic traits produces three distinct demographic patterns:

• • All three are depicted and explained in NCERT Figure 7.8.

Genetic drift refers to stochastic (random sampling) fluctuations in allele frequencies from generation to generation in small, isolated populations. It operates independently of natural selection (often fixing neutral or deleterious alleles purely by chance, such as in the founder effect or bottleneck effect). Therefore, natural selection does NOT lead to genetic drift.

• • Statement (b) must be excluded.

Statements (a), (c), and (d) are legitimate outcomes of natural selection, while (b) is an independent evolutionary mechanism. The matching combination is Option (2).

• • Matches official NTA final answer key Option B / (2).

In a large, randomly mating diploid population where evolutionary forces (mutation, gene flow, genetic drift, natural selection) are absent, allele frequencies and genotype frequencies remain constant from generation to generation.

• • p = frequency of dominant allele A.
• • q = frequency of recessive allele a.
• • p² = frequency of homozygous genotype AA.
• • 2pq = frequency of heterozygous genotype Aa.
• • q² = frequency of homozygous genotype aa.

We are given that the frequency of allele A is $p = 0.1$. To find the frequency of individuals possessing genotype AA:

• • p² = 0.01 (or 1% of the population).

Option (1) gives 0.01, which is exact. Option (2) gives 0.02. Option (3) gives 0.10 (allele frequency p). Option (4) gives 0.99. Option (1) is correct.

• • Matches official NTA final answer key Option A / (1).

Ernst Haeckel proposed embryological support for evolution based on the observation of certain features during embryonic stages common to all vertebrates that are absent in adults (e.g., vestigial gill slits in human embryos).

• • Von Baer noted that embryos never pass through the adult stages of other animals; hence Haeckel’s generalization is not an accepted evolutionary law.

Homologous organs (divergent evolution, e.g., vertebrate forelimbs), analogous organs (convergent evolution, e.g., sweet potato and potato), and industrial melanism (natural selection in Biston betularia) are fully accepted empirical evidences.

• • Thus, Option (3) is the single non-accepted proposal.

Anthropological and genetic evidence documented in NCERT confirms that Homo sapiens arose in Africa and moved across continents and developed into distinct races.

• • Australia was colonized much later via maritime migration.

During the ice age between 75,000–10,000 years ago, modern Homo sapiens arose. Pre-historic cave art developed about 18,000 years ago, and agriculture started around 10,000 years back.

• • Cave paintings at Bhimbetka rock shelter date back to ~18,000 years ago.

Adaptive radiation within a single lineage produces diverse forms (e.g., Darwin’s finches on Galapagos or Australian marsupials starting from an ancestral stock).

• • Marsupials radiated into marsupial mole, banded anteater, Tasmanian wolf, sugar glider, etc.

When two independent lineages (placental mammals and Australian marsupials) undergo adaptive radiation into similar ecological niches, species in both lineages evolve analogous structures and similar appearances. This parallel adaptation of different lineages to similar environmental pressures is convergent evolution.

• • Placental anteater resembles Numbat; Lemur resembles Spotted cuscus; Bobcat resembles Tasmanian tiger cat.

Whales, bats, cheetah, and humans (all mammals) share similarities in the pattern of bones of forelimbs. Though these forelimbs perform different functions (whale for swimming, bat for flying, cheetah for running, human for grasping), they are homologous organs showing divergent evolution.

• • Assertion (A) is completely true.

Homology is defined as structural similarity due to common ancestry and developmental origin, even if adapted to different functions in different habitats. Because these mammalian forelimbs share the exact same skeletal elements (humerus, radius, ulna, carpals, metacarpals, and phalanges), Reason (R) is true and perfectly explains Assertion (A).

• • Analogy, in contrast, represents different structures evolving for the same function (convergent evolution).

Examining the developmental genesis of both storage organs:

• • Potato (*Solanum tuberosum*): An underground modified stem (stem tuber). It bears nodes ("eyes" with scale leaves and axillary buds) and internodes, characteristic of cauline anatomy.
• • Sweet potato (*Ipomoea batatas*): A modified adventitious root (root tuber). It lacks nodes, internodes, and scale leaves.

Relating structure and function to evolutionary trajectories:

• • Analogy: Structures that are not anatomically similar (different embryonic origins) but perform similar biological functions (both store food/starch underground).
• • Convergent Evolution: Different ancestral structures independently evolve similar phenotypic adaptations in response to similar selective pressures or habitats.
• • NCERT states verbatim: "Sweet potato (root modification) and potato (stem modification) is another example for analogy... Analogous structures are a result of convergent evolution."

The correct combination of terms is Analogy and Convergent evolution, corresponding to Option (1).

The evolutionary progression of genus Homo documented in NCERT follows: 1. Homo habilis: First hominid tool-maker, brain 650-800 cc (Stage A). 2. Homo erectus: Java man around 1.5 million years ago, brain ~900 cc (Stage D). 3. Neanderthal man (Homo neanderthalensis): Lived in near east and central Asia between 100,000-40,000 years ago, brain 1400 cc (Stage C). 4. Homo sapiens: Modern human species arose in Africa and migrated between 75,000-10,000 years ago (Stage B).

From past to recent, the sequence is uniquely A -> D -> C -> B.

Analogy refers to structures that are not anatomically similar though they perform similar functions. It is the result of convergent evolution—different structures evolving for the same function and hence having similarity.

NCERT states: "Other examples of analogy are the eye of the octopus and of mammals or the flippers of Penguins and Dolphins. One can say that it is the similar habitat that has resulted in selection of similar adaptive features in different groups of organisms but toward the same function: this is convergent evolution."

This principle states that allele frequencies in a population are stable and is constant from generation to generation. The gene pool (total genes and their alleles in a population) remains a constant. This is called genetic equilibrium. Sum total of all the allelic frequencies is 1 ($p^2 + 2pq + q^2 = 1$).

NCERT lists five factors known to affect Hardy-Weinberg equilibrium: (i) Gene migration or gene flow (ii) Genetic drift (iii) Mutation (iv) Genetic recombination (v) Natural selection

Gene migration (1), Genetic recombination (3), and Genetic drift (4) all alter allelic frequencies and disrupt equilibrium. A constant gene pool (2) describes the maintenance of equilibrium itself, thus having no disruptive effect.

The geological history of life on Earth is partitioned into major eras: 1. Proterozoic Era (Precambrian): Characterized by the dawn of multicellular life and lower invertebrates (B -> I). 2. Paleozoic Era: Spans Cambrian to Permian, known for the proliferation of marine invertebrates, early jawless and jawed fishes (Devonian: Age of Fishes), and amphibians (Carboniferous) (D -> II). 3. Mesozoic Era: Spans Triassic, Jurassic, and Cretaceous, celebrated as the Age of Reptiles (dinosaurs) and origin of birds (A -> III). 4. Cenozoic Era: Spans Tertiary and Quaternary, recognized as the Age of Mammals (C -> IV).

A-III, B-I, C-IV, D-II matches Option (2).

In Australia, an ancestral marsupial stock underwent adaptive radiation to occupy diverse ecological niches in geographic isolation:

Placental mammals evolved parallel convergent phenotypes resembling these marsupials:

Options 1, 2, and 4 all contain placental mammals (Lemur, Bobcat, Mole, Flying squirrel). Only Option (3) consists entirely of Australian marsupials.

Genetic drift (Sewall Wright effect) refers to the random, non-directional changes in allele frequencies within a gene pool occurring purely due to chance sampling in small populations:

When a small subset of individuals disperses from a large parental population to colonize a previously unoccupied habitat, they serve as the "founders." By chance, the allele frequencies of these founders differ substantially from the parent gene pool.

Over generations, the new colony evolves distinct genotype frequencies, and the original drifted population becomes founders of a distinct lineage or new species. This special case of genetic drift is termed the Founder Effect.

- (a) Adaptive Radiation: The evolutionary divergence of members of a single ancestral species into a diverse array of ecologically different niches within a geographical area. Exemplified by Darwin’s Finches in the Galápagos archipelago, radiating from an ancestral South American seed-eating finch into insect-eating, cactus-feeding, and vegetarian beaks. - (b) Convergent Evolution: Unrelated evolutionary lineages independently evolve similar morphological adaptations and analogous structures in response to similar environmental pressures. Exemplified by the wings of a butterfly (insect) and bird (avian), which share the functional capacity for flight despite having totally distinct developmental origins. - (c) Divergent Evolution: Descendants from a common ancestor evolve differences in homologous structures adapted for divergent modes of life. Exemplified by the bones of forelimbs in Man and Whale (sharing humerus, radius, ulna, carpals, metacarpals, and phalanges despite differing functions in grasping vs swimming). - (d) Evolution by Anthropogenic Action: Artificial directional natural selection driven by human industrial and agricultural activities. Exemplified by the rapid selection of resistant varieties of pests, weeds, and microbes due to excessive use of chemical herbicides, pesticides, and antibiotics.

Matching sequence is: (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i). This corresponds unambiguously to Option (1).

In 1953, Stanley L. Miller, an American scientist, created electric discharge in a closed flask containing CH4, H2, NH3, and water vapor at 800°C, simulating the prebiotic reducing atmospheric conditions of early Earth.

The gas molecules were methane (CH4, not methyl radical CH3), molecular hydrogen (H2), and ammonia (NH3, not ammonium cation NH4). Options (2) and (4) incorrectly use CH3 and NH4.

The electric spark discharge inside the closed simulation chamber operated at 800°C. Options (3) and (4) propose 600°C, which is historically and factually incorrect.

After running the simulation for one week, Miller observed the synthesis of simple amino acids (glycine, alanine, and aspartic acid) from these inorganic precursors.

Ernst Haeckel proposed embryological support for evolution based on the observation of certain embryonic features common to all vertebrates (such as vestigial gill slits in early human embryos) that are absent in adults (Biogenetic law: Ontogeny recapitulates phylogeny).

This proposal was disapproved by Karl Ernst von Baer on the basis of careful comparative observation: he noted that embryos never pass through the adult stages of other animals.

Alfred Wallace worked in the Malay Archipelago and independently conceived natural selection; Charles Darwin authored On the Origin of Species; Alexander Oparin proposed the biochemical origin of life from coacervates.

Karl Ernst von Baer is the definitive scientist who disapproved the embryological hypothesis as stated in NCERT.

Evolution by anthropogenic action refers to evolutionary changes and adaptations in organisms driven, accelerated, or mediated by human activities, such as artificial selection, environmental pollution, pesticide overuse, and antibiotic drug pressure.

Darwin's finches on the Galapagos islands diversified from a common ancestral seed-eating stock through natural adaptive radiation into diverse ecological niches, completely independent of human influence.

Excessive and uncontrolled human application of chemical herbicides and antiparasitic/antibiotic drugs has led to directional selection favoring resistant strains of weeds and resistant eukaryotes/microbes (e.g., chloroquine-resistant Plasmodium, antibiotic-resistant bacteria) within months or years. These are classic anthropogenic evolutionary cases highlighted in NCERT.

Humans have artificially bred and selected various domesticated animal breeds (dogs, cattle, horses) over hundreds of years, representing classic artificial selection by anthropogenic action.

Statements (b), (c), and (d) are all unambiguous examples of evolution brought about by anthropogenic action.

Organs which are anatomically different in structure and embryonic origin but perform similar functions are called analogous structures. Such similarity arises when different organisms adapt to similar habitats or ecological niches, which is termed convergent evolution.

The flippers of penguins (modified wings of birds) and dolphins (modified forelimbs of mammals) are structurally and phylogenetically distinct, yet both function as hydrofoils for swimming in water.

NCERT states explicitly: "Flippers of penguins and dolphins are examples of analogous organs resulting from convergent evolution."

Adaptive radiation leads to divergent evolution from a common ancestor (e.g. Darwin's finches, mammal forelimbs); industrial melanism is natural selection in Biston betularia.