Practice questions › Class 12 › Biology › Evolution Major transitions in the history of life Question 1 Which broad sequence is most consistent with the fossil record?
(a) Aquatic life, land plants, terrestrial vertebrates, later mammalian radiation (b) Modern humans lived alongside the earliest non-avian dinosaurs (c) Land animals colonised Earth before land plants (d) Mammals before cellular life Show answer (a) Aquatic life, land plants, terrestrial vertebrates, later mammalian radiation
Major transitions accumulated over geological time rather than appearing together.
Question 2 What followed the decline of non-avian dinosaurs in the textbook account?
(a) Initial formation of oceans (b) Expansion and diversification of mammals (c) Land animals had colonised before plants appeared (d) Modern humans had already lived with those dinosaurs Show answer (b) Expansion and diversification of mammals
Vacated ecological opportunities contributed to mammalian radiation.
Origin of life and chemical evolution Question 3 Which outcome was directly observed in Miller's simulation?
(a) Organic synthesis in an oxygen-rich atmosphere (b) Formation of amino acids and other simple organic compounds (c) Evolution of bacteria by natural selection (d) Formation of complete living cells Show answer (b) Formation of amino acids and other simple organic compounds
The experiment demonstrated abiotic organic synthesis, not the creation of life.
Question 4 Which gas mixture best represents the reducing model used in the classic experiment?
(a) Oxygen, ozone and nitrogen only (b) A mixture claimed to produce complete living cells directly (c) Methane, ammonia, hydrogen and water vapour (d) Chlorine and sulfur dioxide Show answer (c) Methane, ammonia, hydrogen and water vapour
The apparatus modelled reducing gases and supplied electrical energy.
Evidence from fossils, homology and analogy Question 5 Why do fossils in successive sedimentary layers support evolution?
(a) Only living species can become fossils (b) Rock order never reflects time (c) All fossil-bearing layers must have the same age (d) Different assemblages occur at different dated intervals Show answer (d) Different assemblages occur at different dated intervals
Stratigraphic succession documents appearance, change and extinction.
Question 6 Similar gene sequences in diverse organisms provide what kind of evidence?
(a) Proof that analogous organs are homologous (b) Proof that mutation never occurs (c) Fossils from all strata must have one age (d) Molecular evidence consistent with shared ancestry Show answer (d) Molecular evidence consistent with shared ancestry
Independent molecular similarity can corroborate anatomical relationships.
Adaptive radiation and convergent evolution Question 7 Why are Darwin's finches an adaptive radiation?
(a) They arose from several unrelated ancestors rather than one stock (b) They are unrelated birds converging on the same form (c) Related descendants diversified into different feeding niches from an ancestral stock (d) All beaks retained one function Show answer (c) Related descendants diversified into different feeding niches from an ancestral stock
Common ancestry plus ecological diversification defines a radiation.
Question 8 Different beak forms among related island finches primarily illustrate what?
(a) Convergence among unrelated finches (b) Diversification beginning from unrelated ancestors (c) Hardy-Weinberg equilibrium in every population (d) Divergent evolution under different food niches Show answer (d) Divergent evolution under different food niches
Selection in different niches can separate descendant forms.
Darwinian natural selection and fitness Question 9 In evolutionary biology, which organism has greater fitness in a given habitat?
(a) The largest member of the population (b) The one leaving more viable fertile offspring (c) An individual that develops a needed trait during life (d) The physically strongest individual even if sterile Show answer (b) The one leaving more viable fertile offspring
Fitness is measured through genetic contribution to later generations.
Question 10 Two variants survive equally, but one produces twice as many fertile offspring. What follows?
(a) Both variants have identical fitness because survival is equal (b) The less fertile individuals will acquire greater reproduction during life (c) No frequency can change across generations (d) Its alleles are expected to increase under those conditions Show answer (d) Its alleles are expected to increase under those conditions
Differential reproduction can drive selection even when adult survival is similar.
Evolutionary forces and modes of selection Question 11 What distinguishes genetic drift from natural selection?
(a) Selection is random with respect to fitness (b) Drift always improves adaptation (c) Drift is chance-driven sampling of alleles (d) Gene flow cannot alter allele frequencies Show answer (c) Drift is chance-driven sampling of alleles
Sampling error can shift frequencies regardless of adaptive value.
Natural selection observed in real time Question 12 Why did dark moth frequency rise on soot-darkened trunks?
(a) Soot permanently dyed every moth and its eggs (b) White moths ceased to reproduce anywhere (c) Dark moths were less conspicuous to predators and left more offspring (d) Selection immediately eliminated every pale moth Show answer (c) Dark moths were less conspicuous to predators and left more offspring
Camouflage changed differential survival of inherited colour variants.
Mutation, variation and speciation Question 13 Why can geographic isolation promote speciation?
(a) It makes both populations genetically identical (b) Speciation proceeds equally well with free gene flow. (c) Reduced gene flow allows populations to diverge independently (d) It removes natural selection Show answer (c) Reduced gene flow allows populations to diverge independently
Independent mutation, drift and selection accumulate when interbreeding is limited.
Hardy-Weinberg genetic equilibrium Question 14 What does Hardy-Weinberg equilibrium provide?
(a) A guarantee that mutation is rapid (b) A measure of individual strength (c) A null expectation of stable allele and genotype frequencies (d) Proof by itself that evolution is occurring Show answer (c) A null expectation of stable allele and genotype frequencies
Observed departures prompt investigation of evolutionary forces or assumptions.
Origin and evolution of humans Question 15 According to NCERT, what was the approximate brain capacity of Homo habilis?
(a) 1400 cc (b) 650–800 cc (c) 900 cc (d) 450 cc Show answer (b) 650–800 cc
NCERT assigns a brain capacity of 650–800 cc to Homo habilis and about 1400 cc to Neanderthals.
Does a bacterium evolve because it needs to survive? Wrong
An antibiotic makes each bacterium develop the resistance it needs.
Why it feels right. The resistant population appears after antibiotic exposure.
Right
Selection changes how common heritable traits are across generations.
Worked example
Susceptible
99 before exposure → Killed in this example
Resistant
1 before exposure → Survives → Resistant descendants multiply
The resistant variant exists before exposure. Removing susceptible cells changes which variant is left to reproduce. Imagine 99 susceptible bacteria and 1 already resistant bacterium. If exposure kills the susceptible ones, the resistant survivor can multiply and make resistance common. Previous chapter Molecular Basis of Inheritance Next chapter Human Health and Disease 
