Samacheer Kalvi 10th Science Chapter 18 Short Answer Questions — Evolution with Answers
Short answer questions from Samacheer Kalvi Class 10 Science Chapter 18 Evolution with detailed answers for 2 and 3 mark questions.
Updated 24 May 20265 min read
Chapter 18 — Evolution: Short Answer Questions
1. What is evolution? Briefly describe the chemical evolution of life (Oparin-Haldane theory).
Answer
Evolution is the gradual change in the inherited characteristics of biological populations over successive generations, leading to the formation of new species.
Chemical Evolution (Oparin and Haldane): The early Earth (about 4 billion years ago) had reducing atmosphere: methane (CH₄), ammonia (NH₃), hydrogen (H₂), water vapour (H₂O) — no free oxygen.
Stages: 1. Inorganic to organic molecules: Energy from lightning, UV radiation, and heat caused these gases to react → formed simple organic molecules (amino acids, sugars, nucleotides) 2. Miller-Urey Experiment (1953) proved this: They simulated early Earth conditions in a laboratory and produced amino acids from inorganic gases 3. Formation of polymers: Simple organic molecules combined → proteins, nucleic acids 4. Protocells: Macromolecules clustered in droplets with membranes ("coacervates") 5. First living cells: Protocells with self-replicating RNA → first cells (prokaryotes) about 3.8 billion years ago
2. Explain Darwin's Theory of Natural Selection.
Answer
Charles Darwin (1809–1882) proposed the theory of evolution by natural selection after his voyage on HMS Beagle.
Key points:
1. Overproduction: All organisms reproduce more offspring than can possibly survive.
2. Struggle for existence: Due to limited resources (food, space, mates), organisms compete with each other and with the environment.
3. Variation: Individuals of a population show heritable variations. No two individuals are exactly alike.
4. Natural selection: Individuals with favourable variations (better adapted to environment) have a higher chance of surviving and reproducing — "survival of the fittest" (Herbert Spencer's phrase; Darwin called it "natural selection").
5. Inheritance: Favourable variations are passed on to offspring.
6. Speciation: Over many generations, accumulated changes in populations lead to formation of new species.
Example: In a population of giraffes, those with longer necks could reach more leaves → better survival → long necks became common.
3. What are the evidences of evolution?
1. Fossil record:
Answer
Fossils are preserved remains of organisms in sedimentary rocks
Older fossils are simpler; newer fossils are more complex
Show gradual changes and transitional forms (e.g., Archaeopteryx — dinosaur-bird transition)
2. Homologous organs (comparative anatomy):
Answer
Organs with same basic structure but different functions in different species
Evidence of divergent evolution from a common ancestor
Example: Forelimbs of humans, whales, bats, horses
3. Analogous organs:
Answer
Organs with different structures but similar functions
Evidence of convergent evolution — unrelated organisms adapt to similar environments
Example: Wings of birds and insects
4. Vestigial organs:
Answer
Reduced, non-functional organs that were functional in ancestors
Evidence that the organism descended from ancestors that used them
Example: Wisdom teeth, coccyx (tailbone), appendix, ear muscles in humans
5. Embryology:
Answer
Embryos of different vertebrates (fish, frog, bird, human) look similar in early stages
Suggests common ancestry
6. Molecular evidence:
Answer
DNA and protein sequences are similar in related organisms
4. Differentiate between homologous and analogous organs with examples.
Answer
Feature
Homologous Organs
Analogous Organs
Structure
Same basic structure (bones) — common origin
Different structures — different origins
Function
Different functions
Same function
Significance
Evidence of divergent evolution from a common ancestor
Evidence of convergent evolution — similar environments shape different organisms similarly
Example
Forelimbs of humans, bat, whale, horse — all have humerus, radius, ulna
Wings of birds (modified forelimbs) and wings of insects (modified body wall)
Another example
Vertebrate hearts — all have similar structure
Eyes of vertebrates and octopus — similar function, different origin
5. What are vestigial organs? Give examples from humans. What do they tell us about evolution?
Answer
Vestigial organs are reduced, degenerated, non-functional structures in an organism that were functional in its ancestors.
Examples in humans:
Vestigial organ
Functional ancestor
Coccyx (tailbone)
Tail in primate ancestors
Wisdom teeth
Ancestors needed extra molars for plant diet
Appendix
Caecum for digesting plant cellulose in herbivore ancestors
Ear muscles (auricular muscles)
Used to move ears to detect sound (still functional in some animals)
Nictitating membrane (plica semilunaris)
Third eyelid functional in birds and reptiles
Body hair and goosebumps
Fur for warmth in ancestors; piloerection for appearing larger
Evolutionary significance:
These organs prove that humans share ancestry with organisms that used them
They demonstrate that evolution works by modifying existing structures, not creating from scratch
They provide strong evidence for the theory of evolution — an organism designed from scratch would not have useless organs
6. What is industrial melanism? How does it demonstrate natural selection?
Answer
Industrial melanism refers to the increased frequency of dark (melanic) forms of certain moths in industrial areas due to natural selection.
*The Peppered Moth example (Biston betularia):*
Before industrialisation (pre-1850):
Trees had light-coloured lichen on bark
Light-coloured moths (peppered form) were camouflaged on trees — birds couldn't spot them
Dark (melanic) moths were easily spotted by birds — very rare
After industrialisation:
Factory soot killed lichens; tree trunks became dark and sooty
Light-coloured moths became visible on dark bark — birds ate more of them
Dark moths were now camouflaged on sooty bark — survived better
ResultDark moths became far more common in industrial areas
Lessons:
Natural selection is not a random process — environment determines which variation is "fit"
Selection pressure can change (light moths became common again after air pollution controls)
Evolution can happen in short observable time periods — it doesn't always take millions of years
This is a direct, observed example of natural selection in action.
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Frequently Asked Questions
Darwin's theory: (1) Organisms produce more offspring than can survive (overproduction). (2) Resources are limited, so there is a struggle for existence. (3) Individuals vary in traits; variations are heritable. (4) Individuals with favorable variations survive and reproduce more (survival of the fittest). (5) Over generations, favorable traits become more common in the population — this is natural selection. Over many generations, this leads to evolution of new species.
