Life originated in water (primordial oceans). Earliest life forms were aquatic prokaryotes (stromatolites, cyanobacteria) that evolved in the reducing atmosphere and warm oceans.
Charles Darwin published "On the Origin of Species" (1859), proposing natural selection as the mechanism of evolution.
Hugo de Vries proposed the Mutation theory — that new species can arise by sudden heritable changes (mutations). He emphasized mutation as a source of variation.
Wings of birds and butterflies are analogous structures resulting from convergent evolution — unrelated lineages evolved similar functional structures due to similar selective pressures.
Industrial melanism (e.g., peppered moth Biston betularia) is a classic example of natural selection where darker morphs were favored in polluted environments due to increased crypsis from predators.
Darwin's finches illustrate adaptive radiation: a single ancestral species diversified into multiple species with different beak shapes adapted to distinct ecological niches on the Galápagos Islands.
August Weismann proposed the Germplasm theory — separating germplasm (heritable germ cells) from soma and rejecting the inheritance of acquired characters.
Answer: (c) Carbon dating.
Explanation: Radiometric dating methods (e.g., carbon-14 for relatively recent organic remains, and other isotope systems for older samples) are used to estimate the age of fossils.
Fossils are typically preserved in sedimentary rocks formed by deposition and burial of sediments, which protect remains from destruction and allow fossilization.
Phylogeny denotes the evolutionary history and relationships of an organism or group; ontogeny refers to individual development and paleontology is the study of fossils.
The Mesozoic era is called the 'Age of Reptiles' because dinosaurs and many reptilian groups dominated terrestrial ecosystems during this era.
The Devonian period is known as the 'Age of Fishes' due to the major diversification and dominance of fish groups (e.g., placoderms, early bony fishes).
Modern humans (Homo sapiens) appeared during the Quaternary period (Pleistocene-Holocene epochs) of the Cenozoic era.
Neanderthal brain capacity was large, approximately around 1400 cc (often within the range 1200–1700 cc), comparable to or slightly larger than modern humans.
Darwin emphasized 'struggle for existence' primarily as intraspecific competition (competition among individuals of the same species) leading to natural selection.
Hardy–Weinberg equilibrium requires random mating. Selective or non-random mating violates this assumption and thus disturbs genetic equilibrium.
The early atmosphere (reducing or weakly reducing) is believed to have contained CH4, NH3, H2, H2O vapour, N2 and CO2. This 'primordial soup' provided substrates for abiotic synthesis of organic molecules.
Major gases of primitive Earth: methane (CH4), ammonia (NH3), hydrogen (H2), water vapour (H2O), nitrogen (N2) and carbon dioxide (CO2).
Three major types of fossilization: 1) Permineralization (petrifaction): Mineral-rich water permeates porous tissues; minerals precipitate and replace organic material, preserving hard parts (e.g., petrified wood). 2) Molds and casts (impression fossils): An organism leaves an impression (mold) in sediment; later the mold may be filled by minerals forming a cast that reproduces external form (e.g., shells). 3) Compression and carbonization: Organic material is compressed in sediments; volatile compounds are lost leaving a carbon film/outline (common in plant fossils). (Other modes include preservation in amber, freezing, or tar pits.)
Three major types of fossilization: 1) Permineralization (petrifaction): Mineral-rich water permeates porous tissues; minerals precipitate and replace organic material, preserving hard parts (e.g., petrified wood). 2) Molds and casts (impression fossils): An organism leaves an impression (mold) in sediment; later the mold may be filled by minerals forming a cast that reproduces external form (e.g., shells). 3) Compression and carbonization: Organic material is compressed in sediments; volatile compounds are lost leaving a carbon film/outline (common in plant fossils). (Other modes include preservation in amber, freezing, or tar pits.)
Divergent evolution: Related species evolve different traits from a common ancestor, producing homologous structures. Example: forelimbs of vertebrates (human arm, bat wing, whale flipper) adapted for different functions. Convergent evolution: Unrelated lineages evolve similar traits independently due to similar environmental pressures, producing analogous structures. Example: wings of birds (vertebrates) and wings of butterflies (insects) — similar function but different ancestry.
Divergent evolution: Related species evolve different traits from a common ancestor, producing homologous structures. Example: forelimbs of vertebrates (human arm, bat wing, whale flipper) adapted for different functions. Convergent evolution: Unrelated lineages evolve similar traits independently due to similar environmental pressures, producing analogous structures. Example: wings of birds (vertebrates) and wings of butterflies (insects) — similar function but different ancestry.
Hardy–Weinberg principle: For a gene with two alleles A and a, let p = frequency of A and q = frequency of a (p + q = 1). Under ideal conditions (large population, random mating, no mutation, no migration, no selection) genotype frequencies after one generation are p2 (AA), 2pq (Aa) and q2 (aa), and these proportions remain constant generation to generation (p2 + 2pq + q2 = 1). Thus allele and genotype frequencies are in genetic equilibrium when Hardy–Weinberg assumptions hold. Four factors that can disturb genetic equilibrium: 1) Mutation — introduces new alleles or changes frequencies. 2) Gene flow (migration) — movement of individuals/alleles between populations alters frequencies. 3) Genetic drift — random changes in allele frequencies in small populations (bottleneck, founder effect). 4) Natural selection or non-random mating (including inbreeding) — differential reproductive success or mate choice changes genotype and allele frequencies.
Hardy–Weinberg principle: For a gene with two alleles A and a, let p = frequency of A and q = frequency of a (p + q = 1). Under ideal conditions (large population, random mating, no mutation, no migration, no selection) genotype frequencies after one generation are p2 (AA), 2pq (Aa) and q2 (aa), and these proportions remain constant generation to generation (p2 + 2pq + q2 = 1). Thus allele and genotype frequencies are in genetic equilibrium when Hardy–Weinberg assumptions hold. Four factors that can disturb genetic equilibrium: 1) Mutation — introduces new alleles or changes frequencies. 2) Gene flow (migration) — movement of individuals/alleles between populations alters frequencies. 3) Genetic drift — random changes in allele frequencies in small populations (bottleneck, founder effect). 4) Natural selection or non-random mating (including inbreeding) — differential reproductive success or mate choice changes genotype and allele frequencies.
Hardy–Weinberg equilibrium holds only when allele frequencies remain constant (no evolution). - Mutation: produces new alleles or converts one allele to another, changing p and q over time; even low mutation rates gradually shift frequencies so equilibrium is lost. - Natural selection: differential survival and reproduction of genotypes changes allele frequencies; advantageous alleles increase in frequency while deleterious alleles are removed, so genotype proportions deviate from H–W expectations. - Genetic drift: random sampling effects (bottlenecks, founder effects) cause unpredictable changes in allele frequencies, possibly leading to fixation or loss of alleles; drift is strongest in small populations and violates the H–W assumption of infinite population size. Each mechanism therefore causes evolution and prevents the population from remaining in Hardy–Weinberg equilibrium.
All three processes break Hardy–Weinberg equilibrium by changing allele frequencies: mutation introduces new alleles, natural selection alters allele frequencies by differential reproductive success, and genetic drift causes random fluctuations (especially in small populations).
In Darwinian natural selection, fitness is measured by reproductive success — the number of surviving offspring an individual contributes to the next generation. Organisms with heritable variations better adapted to local conditions have higher fitness because they survive more often and produce more descendants. Over generations these advantageous traits increase in frequency. (Note: 'survival of the fittest' summarizes this idea, but fitness refers to reproductive output rather than strength alone.)
Darwin defined fitness as the ability of an organism to survive and reproduce in its environment; individuals with advantageous heritable variation leave more offspring.
Key objections raised historically against Darwin's theory included: - No known mechanism of inheritance (Darwin wrote before Mendelian genetics); blending inheritance seemed to dilute variation. - Question of how useful, complex structures (e.g., eye) could evolve by small steps. - Source of variation: Darwin could not explain how heritable variation arises. - Incomplete fossil record (few transitional forms known in Darwin's time). - Objections to strict gradualism from those favoring saltation (sudden changes). Modern synthesis and genetics addressed many of these objections (Mendelian inheritance, mutation as source of variation, gradual accumulation by selection), but these were the main historical criticisms.
Main historical objections: lack of a hereditary mechanism, blending inheritance problem, origin of new useful variations, unexplained complex organs, missing transitional fossils, and emphasis on gradualism.
Before industrialization, the light (typica) peppered moth was camouflaged on lichen-covered trees and had higher survival. As soot darkened tree trunks during industrialization, light moths became conspicuous to bird predators while darker (melanic) moths were better camouflaged. Predation removed more light individuals, shifting allele frequencies toward the melanic phenotype — a clear case of directional natural selection. This phenomenon is known as industrial melanism.
Example of directional natural selection called industrial melanism: soot-darkening increased predation on light moths so dark (melanic) forms rose in frequency.
Adaptive radiation is the rapid diversification of a single ancestral species into multiple species adapted to different niches. - Darwin's finches (Galápagos): a common ancestor gave rise to several species with specialized beak shapes and feeding habits (seed-eaters, insectivores, cactus-eaters), each adapted to a particular food resource. - Australian marsupials: from common marsupial ancestors evolved many morphologies (marsupial mole, sugar glider, thylacine, wombat etc.) that occupy ecological roles similar to placental mammals elsewhere, showing diversification into available niches. These examples illustrate how isolation and ecological opportunity drive speciation and morphological specialization — the hallmarks of adaptive radiation.
Both represent adaptive radiation: a single ancestral lineage diversified into many species, each adapted to different ecological niches (finches—beak forms for different diets; marsupials—varied forms occupying niches analogous to placental mammals).
August Weismann proposed the germ-plasm theory distinguishing germ cells (heritable) from somatic cells (non-heritable). He performed experiments in which he cut off the tails of mice for many successive generations; offspring still had normal tails, showing that acquired mutilations were not transmitted. This and the conceptual germline–soma barrier refuted Lamarck's idea that acquired somatic changes are inherited.
August Weismann disproved it by germ-plasm theory and experiments (cutting off mice tails for many generations) showing acquired changes are not inherited.
De Vries argued that new species originate by sudden large heritable changes called mutations (discontinuous variation), which can create new species in single steps (saltation). In contrast: - Lamarck attributed evolution to the inheritance of acquired characters produced by use and disuse of organs. - Darwin emphasized gradualism: many small heritable variations accumulated over time by natural selection. Thus De Vries differs by making mutation the primary creative force producing distinct new forms quickly rather than slow accumulation or acquired changes.
De Vries' Mutation theory (saltationism) proposed new species arise by sudden heritable mutations (discontinuous variation), unlike Lamarck's acquired characters by use/disuse and Darwin's gradual accumulation of small variations acted on by natural selection.
Types of selection: - Stabilizing selection: eliminates extremes and favors the average phenotype, reducing variation. Example: human newborns of very low or very high birth weight have higher mortality; intermediate weights have highest fitness. - Directional selection: shifts the population mean toward one extreme phenotype when environmental conditions change. Example: industrial melanism in the peppered moth where darker individuals became favored; antibiotic resistance where resistant bacteria increase in frequency. - Disruptive (diversifying) selection: favors extreme phenotypes at both ends over intermediates; can increase variation and promote speciation. Example: a bird population that feeds on either very small or very large seeds may favor individuals with very small or very large beaks while intermediate beaks are disadvantaged (black‑bellied seedcracker is a classic case). These modes change phenotype distributions differently and have distinct evolutionary consequences.
Stabilizing selection favors intermediate phenotypes (e.g., human birth weight). Directional selection shifts the population mean toward one extreme (e.g., peppered moth industrial melanism, antibiotic resistance). Disruptive selection favors extremes at both ends, potentially splitting a population (e.g., seedcracker finches with very large or very small beaks).
Arranged from older to more recent: - Ramapithecus (older Miocene/early Pliocene ancestor-like forms) - Australopithecus (bipedal hominins, e.g., A. afarensis) - Homo habilis (early Homo with stone tools) - Homo erectus (more advanced, out-of-Africa dispersal) - Homo sapiens (modern humans) Thus the sequence is: Ramapithecus → Australopithecus → Homo habilis → Homo erectus → Homo sapiens.
Correct chronological order: Ramapithecus → Australopithecus → Homo habilis → Homo erectus → Homo sapiens.
Distinctive morphological differences: - Skull: Neanderthals had low, sloping foreheads, prominent supraorbital (brow) ridges, large nasal aperture, occipital bun; modern Homo sapiens have a high vertical forehead, reduced brow ridges and no occipital bun. - Face and jaw: Neanderthals had a prognathic mid-face and generally lacked a well-developed chin; modern humans have a flatter face and a prominent chin. - Postcranium: Neanderthals were more robust and heavily muscled with shorter limbs and a barrel-shaped chest adapted to cold climates; modern humans are more gracile with longer limbs relative to body size. - Cranial capacity: Neanderthals had large braincases (often comparable to or slightly larger than modern humans) but differed in shape. These features make Neanderthals appear stockier and more archaic compared to gracile modern humans.
Neanderthals were more robust with heavy brow ridges, low receding forehead, large nose, occipital bun, projected mid-face, no prominent chin, and stockier build; modern humans are more gracile with vertical forehead and a distinct chin.