Evolution: NEET previous year questions

Convergent evolution produces analogous structures in unrelated lineages performing similar functions, as with flippers of penguins and dolphins, eyes of octopuses and mammals, and wings of butterflies and birds. The forelimbs of whales and bats, however, share the same basic skeletal plan inherited from a common ancestor; they are homologous structures illustrating divergent evolution. Therefore the whale-and-bat forelimbs are the exception.

Along the geological timeline: about 65 mya the dinosaurs suddenly disappeared from the earth (II); about 500 mya invertebrates were formed and became active (IV); about 350 mya jawless fishes probably evolved (I); and about 320 mya seaweeds and a few plants probably existed (III). This gives P-II, Q-IV, R-I, S-III.

The accepted chronological order of human evolution proceeds from Ramapithecus through Homo habilis and Homo erectus to Neanderthal man and finally modern Homo sapiens. Only option (1) reflects this sequence; the others wrongly place Homo sapiens, Ramapithecus or Neanderthal out of order.

Natural selection operates in three modes, distinguished by which part of the trait distribution it favours: stabilising selection favours the average and narrows variation, directional selection shifts the mean toward one extreme, and disruptive selection favours both extremes and can split the population into two peaks. GENETIC DRIFT is not one of them - it is random change in allele frequency caused by chance in small populations, and is explicitly a non-selective mechanism. NCERT Class 12, Evolution.

Under Hardy-Weinberg equilibrium the genotype frequencies follow $p^2 + 2pq + q^2 = 1$, where $p^2$ is the frequency of the homozygous dominant genotype. With $p = 0.1$, the frequency of AA is $p^2 = 0.01$. The rare-allele lesson is worth noting: a 10 per cent allele frequency produces only 1 per cent homozygotes, which is why recessive disorders remain rare even when carriers are not. NCERT Class 12, Evolution.

Ernst Haeckel's recapitulation proposal claimed that embryonic development repeats ancestral adult stages, but Karl Ernst von Baer's observations disproved that claim; NCERT therefore treats this proposed support as invalid evidence. Fossils are palaeontological evidence, analogous wings illustrate convergent evolution, and homologous forelimbs illustrate divergent evolution. NTA's paper spelled the name Heckel; it is corrected to Haeckel. NCERT Class 12, Evolution (evidence for evolution).

Modern Homo sapiens arose in Africa and migrated across continents. In the NCERT timeline used by this question, their emergence is placed during the ice age, about 75,000 to 10,000 years ago. Statement I names the wrong continent; statement II follows that textbook timeline.

Two adaptive radiations happened independently - one among placental mammals and one among Australian marsupials - yet each produced strikingly similar forms occupying equivalent niches, such as the placental wolf and the Tasmanian wolf, or the flying squirrel and the flying phalanger. When UNRELATED lineages come to resemble one another under similar selection pressures, that is convergent evolution. NCERT Class 12, Evolution.

Homology is defined by shared underlying anatomy inherited from a common ancestor, whatever the organ is now used for. The forelimbs of humans, bats, cheetahs and whales all contain the same bones - humerus, radius, ulna, carpals, metacarpals and phalanges - arranged in the same pattern despite performing very different functions. That common structural plan is precisely what makes them homologous, so R explains A. NCERT Class 12, Evolution.

S.L. Miller's experiment used a mixture of $\mathrm{CH}_{4}$, $\mathrm{H}_{2}$, $\mathrm{NH}_{3}$, and water vapor at a high temperature (800°C) to simulate early Earth conditions and produce amino acids. Chapter: Evolution.

Karl Ernst von Baer criticized the idea that embryos of different species pass through the same stages of development, which was a key argument for embryological support of evolution. Chapter: Evolution.

Flippers of penguins and dolphins are examples of convergent evolution, where unrelated organisms develop similar traits due to similar environmental pressures. Chapter: Evolution.

Herbicide-resistant weeds, drug-resistant eukaryotes and human-created dog breeds reflect anthropogenic selection. Darwin's finches arose through natural environmental selection, so (II), (III) and (IV) are correct. Chapter: Evolution.