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Evidences of Evolution

BiologyEvolutionFor NEET aspirants

Evidences of evolution come from many quarters: fossils in rock layers, embryos, comparative anatomy, biochemistry, artificial breeding and the moths of industrial England. This page also explains homologous and analogous organs, resistance to pesticides and antibiotics, Darwin's finches and adaptive radiation in Australian marsupials, as in the NCERT Class 12 chapter Evolution. NEET often asks examples of homologous and analogous organs, the moth story and the difference between adaptive radiation and convergent evolution in questions on the evidences of evolution.

On this page1Fossils2Embryology3Comparative anatomy4Breeding5Industrial melanism6Anthropogenic evolution7Adaptive radiation8Exam essentials9Quick revision10Solved examples11Practice
Key Points at a Glance
  1. ★ Must learn Fossils are remains of hard parts of life forms found in rocks; their study gives paleontological evidence.
  2. Embryological evidence (vestigial gill slits) was proposed by Ernst Heckel and disproved by Karl Ernst von Baer.
  3. ★ Must learn Homologous organs: same basic structure and origin, though functions may differ; they arise by divergent evolution and show common ancestry.
  4. ★ Must learn Analogous organs: different structures, similar function; they arise by convergent evolution.
  5. Similar proteins and genes in diverse organisms point to shared ancestry (biochemical evidence).
  6. ★ Must learn England: 1850s more white-winged moths; 1920 more dark-winged (melanised) moths on soot-darkened trees.
  7. Resistance to herbicides, pesticides and antibiotics is evolution by anthropogenic action, seen within months or years.
  8. Evolution is a stochastic process, not a directed one.
  9. ★ Must learn Adaptive radiation: many species from one point in an area, radiating into different habitats; Darwin's finches, Australian marsupials.
  10. More than one adaptive radiation in an isolated area gives convergent evolution (placental wolf and Tasmanian wolf).

1. Paleontological Evidence: Fossils

  • Evidence that evolution has taken place on earth comes from many quarters.
  • Fossils: remains of hard parts of life forms found in rocks.
  • Rocks form sediments; a cross-section of the earth's crust shows sediments laid one over another during its long history.
  • Rock sediments of different ages contain fossils of different life forms, which probably died while that sediment was forming.
  • Some fossils look like modern organisms; others represent extinct organisms, such as dinosaurs.
Family tree of dinosaurs and their living relatives, crocodiles and birds A branching family tree rising from one common stock. Five branches end, showing extinct groups: Stegosaurus, Triceratops, Pteranodon, Brachiosaurus and Tyrannosaurus. Two central lines run on to the present: the crocodilian line, leading to modern crocodiles, and the line through Archaeopteryx, leading to modern birds. Triceratops Tyrannosaurus Pteranodon Crocodilian Archaeopteryx Stegosaurus Brachiosaurus
Figure 1: A family tree of dinosaurs and their living modern-day counterparts, crocodiles and birds. Five branches end because those groups became extinct; two lines run on to the present.
  • A study of fossils in different sedimentary layers shows the geological period in which each organism existed.
  • Life forms varied over time, and certain life forms are restricted to certain geological time-spans.
  • Hence, new forms of life arose at different times in the history of the earth.
  • ★ Exam imp Paleontological evidence: all this evidence from fossils.
  • The ages of fossils are calculated by radioactive dating.
Extra Depth: Radioactive dating measures how much of a radioactive element in a rock or fossil has decayed. Each such element decays at a fixed rate, so the fraction left tells the age of the sample.
Memory Trick The Tiny Pet Can Absolutely Swim Backwards: Triceratops, Tyrannosaurus, Pteranodon, Crocodilian, Archaeopteryx, Stegosaurus, Brachiosaurus, the seven names on the dinosaur family tree. Only the crocodilian and the Archaeopteryx (bird) lines reach the present.
Key idea
Fossils in dated rock layers show that life forms changed over time and that new forms arose at different times.

2. Embryological Evidence

  • Ernst Heckel (also spelt Haeckel) proposed embryological support for evolution.
  • It rested on features seen in the embryos of all vertebrates but absent in the adults.
  • ★ Exam imp Example: embryos of all vertebrates, including humans, develop a row of vestigial gill slits just behind the head.
  • Gill slits are a functional organ only in fish; they are not found in any other adult vertebrate.
  • Karl Ernst von Baer disproved this proposal after careful study.
  • He noted that embryos never pass through the adult stages of other animals.
NEET Focus Heckel proposed; von Baer disproved. A statement that "a human embryo passes through the adult stage of a fish" is false. Vestigial gill slits appear in all vertebrate embryos, but gill slits work only in fish.
Key idea
Shared embryonic features such as gill slits were offered as evidence, but embryos do not repeat the adult stages of other animals.

3. Comparative Anatomy, Morphology and Biochemistry

  • Comparative anatomy and morphology show similarities and differences among organisms of today and those of the past.
  • Such similarities show whether common ancestors were shared or not.

3.1 Homologous organs: divergent evolution

  • ★ Exam imp Whales, bats, cheetahs and humans (all mammals) share a similar pattern of bones in their forelimbs.
  • The forelimbs do different jobs, yet all have humerus, radius, ulna, carpals, metacarpals and phalanges.
Forelimbs of man, cheetah, whale and bat: homologous organs Silhouettes of a man, a cheetah, a whale and a bat in a row, each with a red arrow pointing down to its forelimb skeleton. The human arm, the cheetah's foreleg, the whale's flipper and the bat's wing all have the same bones in the same order: humerus in the upper arm, radius and ulna in the forearm, then carpals, metacarpals and phalanges. In the flipper the bones are short and broad; in the bat the finger bones are very long and hold up the wing membrane. Labels on the human arm: humerus, radius and ulna, carpals, metacarpals, phalanges. Man Cheetah Whale Bat Humerus Radiusand ulna Carpals Metacarpals Phalanges
Figure 2: Homologous organs in animals: the forelimbs of man, cheetah, whale and bat. All four have the same set of bones, though they do different jobs.
  • In these animals, the same structure developed along different directions as adaptations to different needs.
  • Divergent evolution: this process; the structures formed are homologous.
  • Other examples: vertebrate hearts and brains.
  • In plants: the thorn of Bougainvillea and the tendril of Cucurbita.
Thorn of Bougainvillea and tendril of Cucurbita: homologous organs Two drawings side by side. Left, Bougainvillea: a slender woody stem with several short, sharp, pointed thorns growing out from it. Right, Cucurbita: a climbing shoot with broad, lobed and toothed leaves, open flowers and flower buds, and long, thin tendrils, some coiled into tight spirals. Labels: thorn, tendril. Bougainvillea Cucurbita Thorn Tendril
Figure 3: Homologous organs in plants: the thorn of Bougainvillea and the tendril of Cucurbita. They share an origin but do different jobs.
★ Very important Homologous organs have the same basic structure and origin, though their functions may differ (as in the forelimbs). They arise by divergent evolution, and homology indicates common ancestry.
Extra Depth: Both the thorn of Bougainvillea and the tendril of Cucurbita develop from axillary buds, so both are modified stems. This shared origin is what makes them homologous.
Memory Trick Hungry Rabbits Usually Catch More Pumpkins: Humerus, Radius, Ulna, Carpals, Metacarpals, Phalanges, the forelimb bones from the shoulder to the fingers.

3.2 Analogous organs: convergent evolution

  • Analogy refers to the exact opposite situation.
  • Wings of a butterfly and of a bird look alike and do the same job, but they are not anatomically similar.
  • ★ Exam imp Analogous structures result from convergent evolution: different structures evolving for the same function and hence coming to look similar.
  • Other examples: the eye of the octopus and of mammals; the flippers of penguins and dolphins.
  • Sweet potato (a root modification) and potato (a stem modification) are another example of analogy.
  • A similar habitat selects similar adaptive features in different groups of organisms, all towards the same function.
★ Very important Analogous organs are different in structure but similar in function. They arise by convergent evolution in organisms that live in similar habitats.
Memory Trick Analogous organs make a WEFT: Wings (butterfly and bird), Eyes (octopus and mammal), Flippers (penguin and dolphin), Tubers (sweet potato and potato).
Homologous organs
  • Same basic structure and origin
  • Functions may differ
  • Divergent evolution
  • Show common ancestry
  • Forelimbs; hearts; brains; thorn and tendril
Analogous organs
  • Different structures
  • Similar function
  • Convergent evolution
  • Show similar habitats, not common ancestry
  • Wings; eyes; flippers; sweet potato and potato
Tips and Tricks Ask first: same basic structure and origin? If yes, the organs are homologous, whatever their job (forelimbs do different jobs; vertebrate hearts do the same job). If the structures differ but the job is the same, they are analogous. Remember the pairing HD-AC: Homology with Divergent, Analogy with Convergent.

Examples to Remember

Homologous organs (divergent evolution)Analogous organs (convergent evolution)
Forelimbs of whale, bat, cheetah and humanWings of butterfly and of birds
Vertebrate heartsEye of octopus and of mammals
Vertebrate brainsFlippers of penguins and dolphins
Thorn of Bougainvillea and tendril of CucurbitaSweet potato (root) and potato (stem)

3.3 Biochemical evidence

  • Similarities in proteins and genes that perform a given function in diverse organisms give clues to common ancestry.
  • These biochemical similarities point to the same shared ancestry as structural similarities do.
Key idea
Homology (divergent evolution) shows common ancestry; analogy (convergent evolution) shows similar habitats acting on different groups.

4. Evidence from Artificial Breeding

  • Man has bred selected plants and animals for agriculture, horticulture, sport or security.
  • Man has domesticated many wild animals and crops.
  • Intensive breeding has created breeds that differ from other breeds (for example, dogs), yet they remain the same group.
  • Argument: if man could create new breeds within hundreds of years, nature could have done the same over millions of years.

5. Natural Selection in Action: Moths in England

5.1 The observation

  1. A collection of moths made in England in the 1850s, before industrialisation, had more white-winged moths on trees than dark-winged or melanised moths.
  2. A collection from the same area after industrialisation, in 1920, had more dark-winged moths: the proportion was reversed.
Peppered moths before and after industrialisation Two panels, each showing a leafy tree with moths flying around it and a round close-up of its bark. (a) Before industrialisation: most flying moths are white-winged with black speckles and only one is dark; the close-up shows pale lichen patches on the bark, with a white-winged moth almost invisible against them. (b) After industrialisation: most flying moths are dark-winged and only two are white; the close-up shows plain dark bark without lichen, with a dark-winged moth resting on it, hard to see. Labels: lichen-covered bark, white-winged moth, dark-winged moth, dark bark, no lichen. (a) Before industrialisation (b) After industrialisation Lichen-coveredbark White-wingedmoth Dark-wingedmoth Dark bark,no lichen
Figure 4: Peppered moths around the same kind of tree (a) before and (b) after industrialisation. Before, most moths were white-winged and hid on lichen-covered bark; after, most were dark-winged and hid on dark bark without lichen.

5.2 The explanation

  • Predators spot a moth against a contrasting background.
  1. Before industrialisation, a thick growth of almost white lichen covered the tree trunks.
  2. On this background the white-winged moths survived, but the dark-coloured moths were picked out by predators.
  3. After industrialisation, the tree trunks became dark with industrial smoke and soot.
  4. Now the white-winged moths did not survive predators, while the dark-winged (melanised) moths survived.
White-winged and dark-winged moths on tree trunks in an unpolluted and a polluted area Two panels, each with a tree trunk carrying one white-winged moth near the top and one dark-winged moth lower down, and a bird perched on a branch with a red arrow from the bird to one moth. (a) Unpolluted area: the trunk is pale, so the white moth is hard to see and the arrow points to the dark moth, which stands out. (b) Polluted area: factory chimneys give off smoke and the trunk is dark with soot, so the dark moth is hard to see and the arrow points to the white moth. Labels: white-winged moth, dark-winged moth, pale trunk, soot-covered trunk. (a) Unpolluted area (b) Polluted area White-wingedmoth Dark-wingedmoth Pale trunk Soot-covered trunk
Figure 5: White-winged and dark-winged (melanised) moths on tree trunks: (a) in an unpolluted area, (b) in a polluted area. A predator such as a bird picks out the moth that stands out against the bark.
  • Lichens do not grow in polluted areas, so they can be used as industrial pollution indicators.
  • Moths that could camouflage themselves, that is, hide in the background, survived.
  • In areas without industrialisation, such as rural areas, the count of melanic moths was low.
  • So, in a mixed population, those that can better adapt survive and increase in population size.
  • ★ Exam imp No variant is completely wiped out.
Memory Trick Before the smoke, white wins; after the smoke, dark wins. 1850s: white bark (lichen), more white moths. 1920: sooty bark, more dark moths.
NEET Focus The moth story shows a change in the proportion of two existing forms, not the sudden appearance of a new form. Both forms remain; no variant is wiped out. Rural areas kept a low count of melanic moths, which supports the explanation.
Key idea
Predators removed the moths that did not match the bark, so the commoner colour changed with industrial soot.

6. Evolution by Anthropogenic Action

  • Excess use of herbicides and pesticides has resulted in the selection of resistant varieties in a much shorter time.
  • The same is true for microbes against which we use antibiotics, and for eukaryotic organisms or cells against which we use drugs.
  • Resistant organisms and cells appear within months or years, not centuries.
  • ★ Exam imp These are examples of evolution by anthropogenic action (action by humans).
  • So evolution is not a directed process in the sense of determinism.
  • It is a stochastic process, based on chance events in nature and chance mutations in organisms.
★ Very important Evolution is a stochastic process: it rests on chance events in nature and chance mutations in organisms, and is not directed towards a goal.
Quick Recall: tap to check
Who proposed embryological support for evolution, and who disproved it?
Ernst Heckel proposed it; Karl Ernst von Baer disproved it.
Name the bones common to the forelimbs of whale, bat, cheetah and human.
Humerus, radius, ulna, carpals, metacarpals and phalanges.
Why are lichens called industrial pollution indicators?
They do not grow in polluted areas.
Give two examples of evolution by anthropogenic action.
Selection of herbicide- or pesticide-resistant varieties, and of antibiotic-resistant microbes.
Memory Trick Fine Elephants Always Bathe Before Morning Rain: Fossils, Embryos, Anatomy (homology and analogy), Biochemistry, Breeding, Moths, Resistance, the lines of evidence in the order they appear on this page.
Key idea
Human use of pesticides, herbicides, antibiotics and drugs selects resistant forms within years, showing selection by chance variation.

7. Adaptive Radiation

7.1 Darwin's finches

  • During his journey, Darwin visited the Galapagos Islands and saw an amazing diversity of creatures.
  • Small black birds, later called Darwin's finches, amazed him: there were many varieties on the same island.
  • He conjectured that all the varieties had evolved on the island itself.
  • ★ Exam imp From the original seed-eating features, many other forms with altered beaks arose, so finches became insectivorous and vegetarian.
Variety of beaks of Darwin's finches and the food each beak suits Heads of four finches side by side, each with the food its beak suits shown below it: the large ground finch, with a very deep, thick, crushing beak, and hard seeds; the warbler finch, with a thin, pointed beak, and insects; the cactus finch, with a long, strong, sharp-tipped beak, and cactus flowers and fruit; the woodpecker finch, holding a twig in its beak, and insect larvae in wood. Large groundfinch Warbler finch Cactus finch Woodpeckerfinch Hard seeds Insects Cactus flowersand fruit Insect larvaein wood
Figure 6: Variety of beaks of the finches Darwin found in the Galapagos Islands. Each beak shape suits a different diet.
★ Very important Adaptive radiation: the evolution of different species in a given geographical area, starting from a point and radiating to other areas of geography (habitats). Darwin's finches are one of the best examples.
Darwin's finches: many forms from one ancestral finch A branching tree on the left starts at the head of a common ancestor finch and splits into three groups of finch heads arranged in rows, each with a picture of its food and its name: warbler finch, insects; woodpecker finch, insect larvae, using a twig; vegetarian finch, buds, flowers and fruit; small ground finch, small seeds; large ground finch, large, hard seeds; cactus finch, cactus flowers and fruit; sharp-beaked ground finch, seeds and also seabird eggs. The beaks range from thin and pointed to short, deep and thick. Commonancestor Warbler finchInsects Woodpecker finchInsect larvae; uses a twig Vegetarian finchBuds, flowers and fruit Small ground finchSmall seeds Large ground finchLarge, hard seeds Cactus finchCactus flowers and fruit Sharp-beaked ground finchSeeds; also seabird eggs
Figure 7: Adaptive radiation of Darwin's finches. From one seed-eating ancestral finch arose a warbler finch, tree finches and ground finches, each with a beak suited to its food.

7.2 Australian marsupials

  • A number of marsupials, each different from the others, evolved from an ancestral stock.
  • All of them evolved within the Australian island continent: another example of adaptive radiation.
Adaptive radiation of marsupials of Australia A circle labelled marsupial radiation sits at the centre of a layout marked Australia, with arrows radiating out to ten different marsupials placed around it: Tasmanian wolf, tiger cat, banded anteater, marsupial rat, kangaroo, wombat, bandicoot, koala, marsupial mole and sugar glider. Marsupial radiation AUSTRALIA Tasmanian wolf Sugar glider Tiger cat Marsupial mole Koala Bandicoot Wombat Kangaroo Banded anteater Marsupial rat
Figure 8: Adaptive radiation of marsupials of Australia. Many different marsupials arose from one ancestral stock within the same continent.

Examples to Remember

Marsupials (adaptive radiation in Australia)Marsupials (continued)
Tasmanian wolfTiger cat
Banded anteaterMarsupial rat
KangarooWombat
BandicootKoala
Marsupial moleSugar glider

7.3 Convergent evolution among Australian mammals

  • When more than one adaptive radiation occurs in an isolated geographical area (representing different habitats), one can call this convergent evolution.
  • Placental mammals in Australia also show adaptive radiation, into a variety of forms.
  • ★ Exam imp Each placental form appears similar to a corresponding marsupial, for example the placental wolf and the Tasmanian wolf (a marsupial).
Convergent evolution of Australian marsupials and placental mammals Two columns of seven matching pairs. Each placental mammal sits opposite the Australian marsupial that looks and lives like it: mole and marsupial mole; anteater and numbat (anteater); mouse and marsupial mouse; lemur and spotted cuscus; flying squirrel and flying phalanger; bobcat and Tasmanian tiger cat; wolf and Tasmanian wolf. Placental mammals Australian marsupials Mole Anteater Mouse Lemur Flying squirrel Bobcat Wolf Marsupial mole Numbat (anteater) Marsupial mouse Spotted cuscus Flying phalanger Tasmanian tiger cat Tasmanian wolf
Figure 9: Convergent evolution of Australian marsupials and placental mammals. Each marsupial resembles the placental mammal that lives in a similar way, though the two are not closely related. Test yourself hides the marsupial names.
Tips and Tricks Three marsupials borrow the placental name (marsupial mole, marsupial mouse, Tasmanian wolf), and the numbat keeps "anteater" in brackets. Learn the other three as a set: lemur and spotted cuscus, flying squirrel and flying phalanger, bobcat and Tasmanian tiger cat.
  • Homology is accounted for by the idea of branching descent.
  • Comparative anatomy, fossils and comparative biochemistry all provide evidence for evolution.
Quick Recall: tap to check
What did the original Darwin's finches eat, and what forms arose?
They were seed-eating; insectivorous and vegetarian forms with altered beaks arose.
Define adaptive radiation.
Evolution of different species in a given geographical area, starting from a point and radiating into different habitats.
Name the marsupial counterpart of the flying squirrel.
The flying phalanger.
When can more than one adaptive radiation be called convergent evolution?
When it occurs in an isolated geographical area representing different habitats.
Key idea
Adaptive radiation spreads one stock into many habitats; two radiations in one isolated area give look-alike pairs by convergence.

8. Exam Essentials

Pairs to Match

Organism or termMatches with
FossilsPaleontological evidence
Radioactive datingAge of fossils
Ernst HeckelEmbryological support: vestigial gill slits
Karl Ernst von BaerEmbryos never pass through adult stages of other animals
Forelimbs of whale, bat, cheetah and humanHomologous organs
Thorn of Bougainvillea and tendril of CucurbitaHomologous organs in plants
Wings of butterfly and birdAnalogous organs
Eye of octopus and of mammalsAnalogous organs
Sweet potato and potatoAnalogous: root and stem modifications
HomologyDivergent evolution
AnalogyConvergent evolution
LichensIndustrial pollution indicators
Melanised mothsSoot-darkened tree trunks
Darwin's finchesAdaptive radiation, Galapagos Islands
Placental wolf and Tasmanian wolfConvergent evolution
Exceptions
  • Gill slits are functional only in fish; other vertebrates have them only as vestigial structures in the embryo.
  • Embryos do not pass through the adult stages of other animals.
  • Analogous organs look alike but are not anatomically similar.
  • Sweet potato and potato are not homologous: one is a root and the other a stem.
  • In the moth story, no variant was completely wiped out.
  • In rural areas, the count of melanic moths stayed low.
  • Resistance to pesticides and antibiotics appears in months or years, not centuries.
  • Evolution is not a directed process; it is stochastic.

Numbers to Remember

  • 1850s: before industrialisation; more white-winged moths.
  • 1920: after industrialisation; more dark-winged moths.
  • Months or years: time for resistant organisms and cells to appear.
  • 6 kinds of forelimb bones: humerus, radius, ulna, carpals, metacarpals, phalanges.
  • 7 placental and marsupial pairs in the convergent evolution chart.

9. Quick Revision

  • Fossils are remains of hard parts in rocks; layers of different ages hold different fossils.
  • Fossil study (paleontological evidence) shows new forms arose at different times; ages come from radioactive dating.
  • Heckel: vestigial gill slits in all vertebrate embryos; von Baer disproved it.
  • Homologous organs: same structure and origin, function may differ; divergent evolution; common ancestry.
  • Forelimbs of whale, bat, cheetah, human; vertebrate hearts and brains; thorn and tendril.
  • Analogous organs: different structure, same function; convergent evolution.
  • Wings of butterfly and bird; eyes of octopus and mammals; flippers of penguin and dolphin; sweet potato and potato.
  • Similar proteins and genes show common ancestry.
  • Breeding of dogs and crops shows how selection creates new breeds.
  • Moths: 1850s more white; 1920 more dark; predators spot contrast; lichens indicate pollution.
  • Herbicide, pesticide and antibiotic resistance: evolution by anthropogenic action.
  • Evolution is stochastic, based on chance events and chance mutations.
  • Adaptive radiation: Darwin's finches (seed-eating to insectivorous and vegetarian) and Australian marsupials.
  • Placental and marsupial look-alikes in Australia show convergent evolution.
  • Homology is explained by branching descent.

10. Solved Examples

Solved Example 1
Match List I with List II.
List I: A. Homologous organs, B. Analogous organs, C. Industrial melanism, D. Adaptive radiation
List II: I. Darwin's finches, II. Wings of butterfly and bird, III. Thorn of Bougainvillea and tendril of Cucurbita, IV. White- and dark-winged moths in England
Choose the correct answer:
(A) A-II, B-III, C-IV, D-I
(B) A-III, B-II, C-I, D-IV
(C) A-III, B-II, C-IV, D-I
(D) A-IV, B-II, C-III, D-I
Solution:

Answer: (C). Thorn and tendril are homologous (III); butterfly and bird wings are analogous (II); the moths show industrial melanism (IV); Darwin's finches show adaptive radiation (I).

Solved Example 2
Read the statements.
A. Homology indicates common ancestry.
B. The eyes of the octopus and of mammals are homologous.
C. Sweet potato and potato are analogous.
D. Vertebrate hearts are homologous.
E. Analogous structures result from divergent evolution.
Choose the correct answer:
(A) A, B and C only
(B) A, C and D only
(C) B, D and E only
(D) A, D and E only
Solution:

Answer: (B). B is wrong: the two eyes are analogous. E is wrong: analogous structures result from convergent evolution.

Solved Example 3
Arrange the events of the moth story in the correct order.
A. Industrial smoke and soot darken the tree trunks
B. White lichen covers the trunks, and white-winged moths are commoner
C. Predators pick out the white-winged moths against the dark bark
D. Dark-winged moths become commoner
Choose the correct answer:
(A) A, B, C, D
(B) B, A, C, D
(C) B, C, A, D
(D) A, C, B, D
Solution:

Answer: (B). Before industrialisation (B), soot darkens the trunks (A), predators remove the contrasting white moths (C), and dark moths increase (D).

Solved Example 4
Which of the following is an example of evolution by anthropogenic action?
(A) Adaptive radiation of Australian marsupials
(B) Selection of pesticide-resistant varieties
(C) Formation of fossils in rock layers
(D) Vestigial gill slits in vertebrate embryos
Solution:

Answer: (B). Excess use of pesticides by humans has selected resistant varieties within a short time.

Solved Example 5
Statement I: Embryos of all vertebrates, including humans, develop a row of vestigial gill slits.
Statement II: Karl Ernst von Baer showed that embryos pass through the adult stages of other animals.
(A) Both Statement I and Statement II are correct
(B) Both Statement I and Statement II are incorrect
(C) Statement I is correct but Statement II is incorrect
(D) Statement I is incorrect but Statement II is correct
Solution:

Answer: (C). Von Baer showed the opposite: embryos never pass through the adult stages of other animals.

Solved Example 6
Which statement about adaptive radiation is NOT correct?
(A) Darwin's finches are one of its best examples
(B) Australian marsupials evolved from an ancestral stock within Australia
(C) It starts from a point and radiates into different habitats
(D) It means unrelated organisms in similar habitats come to look alike
Solution:

Answer: (D). Unrelated organisms coming to look alike in similar habitats is convergent evolution, not adaptive radiation.

11. Practice Questions

Practice Questions
  1. Match List I with List II.
    List I: A. Ernst Heckel, B. Karl Ernst von Baer, C. Galapagos Islands, D. Lichens
    List II: I. Darwin's finches, II. Pollution indicators, III. Vestigial gill slits as evidence, IV. Embryos never pass through adult stages of other animals
    (A) A-IV, B-III, C-I, D-II (B) A-III, B-IV, C-I, D-II (C) A-III, B-IV, C-II, D-I (D) A-I, B-IV, C-III, D-IIAnswer: (B). Heckel used gill slits, von Baer disproved him, Darwin's finches lived on the Galapagos and lichens indicate pollution.
  2. Read the statements about the moths of England.
    A. In the 1850s white-winged moths were commoner.
    B. After industrialisation, lichen growth increased on trees.
    C. Predators spot moths against a contrasting background.
    D. In rural areas, melanic moths were few.
    E. The white-winged form was completely wiped out.
    Choose the correct answer: (A) A, C and D only (B) A, B and C only (C) B, D and E only (D) A, C, D and E onlyAnswer: (A). Lichens do not grow in polluted areas, and no variant is completely wiped out.
  3. Which pair shows analogous organs? (A) Forelimbs of whale and bat (B) Thorn of Bougainvillea and tendril of Cucurbita (C) Flippers of penguin and dolphin (D) Hearts of vertebratesAnswer: (C). Flippers of penguins and dolphins have different structures but the same function.
  4. Which of the following is NOT an example of homology? (A) Brains of vertebrates (B) Forelimbs of cheetah and human (C) Eyes of octopus and mammals (D) Hearts of vertebratesAnswer: (C). The eyes of the octopus and of mammals are analogous.
  5. Arrange the forelimb bones from the shoulder to the fingers: A. Carpals, B. Humerus, C. Phalanges, D. Radius and ulna, E. Metacarpals
    (A) B, D, A, E, C (B) B, A, D, E, C (C) D, B, A, E, C (D) B, D, E, A, CAnswer: (A). Humerus, radius and ulna, carpals, metacarpals, phalanges.
  6. Statement I: Placental mammals in Australia also show adaptive radiation.
    Statement II: The placental wolf and the Tasmanian wolf are an example of convergent evolution.
    (A) Both statements are correct (B) Both statements are incorrect (C) Statement I is correct but Statement II is incorrect (D) Statement I is incorrect but Statement II is correctAnswer: (A). Each placental form resembles a corresponding marsupial.
  7. Evolution is called a stochastic process because it (A) is directed towards a goal (B) depends on chance events and chance mutations (C) happens only in microbes (D) needs human actionAnswer: (B). It is not directed in the sense of determinism.
  8. Describe one example of adaptive radiation.Answer: Darwin's finches: from a seed-eating ancestor on the Galapagos Islands, many forms with altered beaks arose, including insectivorous and vegetarian finches. (Australian marsupials are another example.)
  9. Activity: Draw the forelimbs of a human, a cheetah, a whale and a bat side by side, and label the bones.Answer: Label humerus, radius, ulna, carpals, metacarpals and phalanges in each; the same bones in the same order show homology.

Common Mistakes to Avoid

Watch out
  • Calling the eyes of the octopus and of mammals homologous: they are analogous.
  • Calling sweet potato and potato homologous: one is a root and the other a stem, so they are analogous.
  • Linking homology with convergent evolution: homology comes from divergent evolution.
  • Writing that embryos pass through the adult stages of other animals: von Baer showed they never do.
  • Writing that gill slits work in adult vertebrates other than fish.
  • Saying the white-winged moths were wiped out after industrialisation: no variant is completely wiped out.
  • Saying that resistance to pesticides or antibiotics needs centuries: it appears within months or years.
  • Treating adaptive radiation and convergent evolution as the same: radiation spreads one stock; convergence makes unrelated forms alike.

Frequently Asked Questions

What is the difference between homologous and analogous organs?

Homologous organs have the same basic structure and origin, though their functions may differ, as in the forelimbs of whales, bats, cheetahs and humans. They arise by divergent evolution and show common ancestry. Analogous organs differ in structure but do the same job, such as the wings of butterflies and birds, and arise by convergent evolution.

Why are fossils called paleontological evidence of evolution?

Fossils are remains of hard parts of organisms preserved in rock layers. Layers of different ages hold fossils of different life forms. Their study shows the geological period of each organism, that life forms changed over time and that new forms arose at different times. Fossil ages are found by radioactive dating.

Why was Heckel's embryological evidence rejected?

Ernst Heckel pointed to features shared by all vertebrate embryos, such as a row of vestigial gill slits behind the head, which work only in fish. Karl Ernst von Baer studied embryos carefully and showed that embryos never pass through the adult stages of other animals, so the proposal was disproved.

How do the moths of England show natural selection?

Before industrialisation, white lichen covered tree trunks and white-winged moths were commoner. After industrialisation, soot darkened the trunks and by 1920 dark-winged moths were commoner. Predators spot moths against a contrasting background, so the camouflaged form survived. Rural areas kept few melanic moths, and no form was wiped out.

What is evolution by anthropogenic action?

It is evolution driven by human activity. Excess use of herbicides, pesticides, antibiotics and drugs has selected resistant weeds, pests, microbes and cells within months or years, not centuries. These examples also show that evolution is a stochastic process based on chance events and chance mutations, not a directed one.

What is adaptive radiation? Give two examples.

Adaptive radiation is the evolution of different species in one geographical area, starting from a point and radiating into different habitats. Darwin's finches on the Galapagos Islands evolved from a seed-eating ancestor into insectivorous and vegetarian forms. The marsupials of Australia, such as the kangaroo, koala and wombat, evolved from one ancestral stock.

How is convergent evolution seen in Australian mammals?

Placental mammals in Australia also radiated into many forms. Each placental form resembles a marsupial that lives in a similar way, for example the placental wolf and the Tasmanian wolf, or the flying squirrel and the flying phalanger. When more than one adaptive radiation occurs in an isolated area, this is called convergent evolution.

Which evidences of evolution are most asked in NEET?

NEET most often asks examples of homologous and analogous organs, the pairing of homology with divergent and analogy with convergent evolution, the moth story with its dates, Heckel and von Baer, adaptive radiation in Darwin's finches and Australian marsupials, and placental and marsupial look-alike pairs.

Previous year questions on Evidences of Evolution

3 questions from past papers, each with a step-by-step solution.

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