🌸Chapter 6
EVOLUTION
( 5 Marks)
1. Explain the chemical origin of
life on Earth.
Answer:
- Primitive Earth: Formed about 4.6 billion years
ago with high temperature, reducing atmosphere (CH₄, NH₃, H₂, and water
vapor), no oxygen or ozone.
- Oparin-Haldane Theory: Life originated from inorganic
molecules through chemical evolution forming simple organic compounds →
complex → coacervates → primitive cells.
- Miller-Urey Experiment: Simulated early Earth’s
conditions with gases and electric sparks; after a week, amino acids were
formed → supported chemical evolution.
- Conclusion: Life originated from
non-living matter by chemical evolution about 3.5 billion years ago.
2. Describe the major evidences that
support evolution.
Answer:
1.
Fossil
Evidence:
o Fossils show progression from simple
to complex forms.
o Transitional fossils like Archaeopteryx
(reptile + bird).
2.
Anatomical
Evidence:
o Homologous organs → common ancestry
(human arm, bat wing).
o Analogous organs → convergent
evolution (bird wing, insect wing).
o Vestigial organs → reduced function
(appendix).
3.
Embryological
Evidence:
o Early embryos of vertebrates show
similarities → common ancestry.
4.
Molecular
Evidence:
o Similar DNA, RNA, and proteins (cytochrome-c).
5.
Biogeographical
Evidence:
o Similar species found in nearby
regions (Darwin’s finches).
3. Describe Darwin’s theory of
natural selection and its main postulates.
Answer:
Main Postulates:
1.
Overproduction: Organisms produce more offspring
than can survive.
2.
Variation: Variations occur naturally among
individuals.
3.
Struggle
for existence:
Competition for food, space, and mates.
4.
Survival
of the fittest:
Individuals with advantageous variations survive.
5.
Inheritance: Favorable traits are inherited by offspring.
Conclusion:
Over time, these changes accumulate → formation of new species.
Example: Darwin’s finches evolved different beaks suited to food
sources.
4. Compare Lamarck’s and Darwin’s
theories of evolution.
Answer:
|
Basis |
Lamarckism |
Darwinism |
|
Scientist |
Jean Baptiste Lamarck |
Charles Darwin |
|
Mechanism |
Inheritance of acquired characters |
Natural selection |
|
Variation |
Not emphasized |
Central concept |
|
Example |
Giraffe neck elongates by stretching |
Giraffes with longer necks survived |
|
Evidence |
No genetic support |
Supported by fossil and observation |
Conclusion:
Darwin’s theory is widely accepted as it is supported by genetics and
experimental evidence.
5. What are homologous and analogous
organs? What do they indicate about evolution?
Answer:
- Homologous organs: Same structure, different
function.
- Example: Forelimbs of humans,
whales, bats.
- Indicate divergent
evolution and common ancestry.
- Analogous organs: Different structure, same
function.
- Example: Wings of birds and
insects.
- Indicate convergent
evolution due to similar environmental pressures.
Thus, comparative anatomy shows adaptive modification from
ancestral forms.
6. Describe the Hardy-Weinberg
principle and the factors that disturb it.
Answer:
Principle:
- Allele frequencies in a
population remain constant from generation to generation if no
evolutionary forces act.
- Represented by:
p2+2pq+q2=1p^2 + 2pq + q^2 = 1p2+2pq+q2=1
where p = dominant allele frequency, q =
recessive allele frequency.
Disturbing Factors:
1.
Mutation
2.
Gene
flow (migration)
3.
Genetic
drift
4.
Natural
selection
5.
Non-random
mating
If these occur → evolution takes place (change in allele
frequencies).
7. Explain industrial melanism as an
example of natural selection.
Answer:
- Before industrialization: Trees
had light-colored bark → light moths survived, dark moths eaten.
- After industrialization: Trees
covered with soot → dark moths camouflaged, survived better.
- Natural selection favored dark
moths in polluted areas.
- When pollution reduced, light
moths became common again.
Conclusion: Natural selection operates depending on environmental conditions.
8. Discuss the evidences of
evolution from fossils.
Answer:
- Definition: Fossils are preserved remains
or traces of ancient life.
- Types of Evidence:
1.
Progressive
development:
Simple → complex life forms.
2.
Transitional
forms: e.g., Archaeopteryx
(link between reptiles & birds).
3.
Fossil
series: e.g.,
horse evolution from Eohippus → Equus.
4.
Dating
techniques:
Carbon-14 and potassium-argon help estimate fossil age.
Conclusion: Fossil evidence supports organic evolution over geological
time.
9. Explain adaptive radiation with
examples.
Answer:
- Definition: Evolution of different species
from a common ancestor in different environments.
- Examples:
1.
Darwin’s
finches:
Different beak shapes adapted to food types.
2.
Australian
marsupials:
Evolved into kangaroo, koala, etc., from a common ancestor.
- Importance: Shows how new species arise by
adapting to new ecological niches.
10. What are the different types of
natural selection? Explain with examples.
Answer:
1.
Stabilizing
selection:
o Favors average phenotype.
o Example: Human birth weight.
2.
Directional
selection:
o Favors one extreme.
o Example: Industrial melanism.
3.
Disruptive
selection:
o Favors both extremes.
o Example: Color forms in snails.
Conclusion: Different types of selection shape genetic composition and
adaptation.
11. What is genetic drift? Explain
its types with examples.
Answer:
- Definition: Random change in allele
frequency in small populations.
Types:
1.
Founder
Effect: Small
group forms a new colony → limited gene pool (e.g., island birds).
2.
Bottleneck
Effect:
Population drastically reduced by disaster → genetic variation decreases.
Result: Leads to evolution independent of natural selection.
12. Describe the major events in the
history of life on Earth.
Answer:
1.
4.6
bya: Earth formed.
2.
3.5
bya: First prokaryotic cells
(anaerobic).
3.
2.0
bya: Eukaryotes appeared.
4.
1.0
bya: Multicellular organisms.
5.
0.5
bya: Marine life diversified.
6.
0.4
bya: Land plants and amphibians evolved.
7.
0.002
bya: Humans evolved.
Conclusion: Life evolved gradually from simple to complex forms.
13. Explain human evolution with
major fossil evidences.
Answer:
1.
Australopithecus: Bipedal, small brain (~500 cc).
2.
Homo
habilis: “Handy
man,” used tools (~700 cc).
3.
Homo
erectus: Used
fire, walked upright (~900 cc).
4.
Neanderthal
man: Cultural development, burials
(~1400 cc).
5.
Homo
sapiens: Modern
man (~1450 cc), highly intelligent.
Conclusion: Human evolution shows gradual brain expansion, bipedalism,
and culture.
14. Describe molecular evidence in
support of evolution.
Answer:
- DNA & Protein Similarity: Common genetic code for all
life forms.
- Examples:
- Human and chimpanzee DNA ~98%
similar.
- Cytochrome-c and hemoglobin
sequences conserved across species.
- Inference: Molecular similarity indicates
common ancestry and divergent evolution.
15. Explain the process of
speciation.
Answer:
- Definition: Formation of new species from
existing ones.
Steps:
1.
Isolation: Populations separated by geography
or behavior.
2.
Variation: Genetic differences accumulate.
3.
Natural
Selection: Different
environments favor different traits.
4.
Reproductive
Isolation:
Interbreeding stops.
5.
Speciation: New species form.
Example: Darwin’s finches on different islands.
16. Discuss the role of continental
drift in evolution.
Answer:
- Earth’s continents were once
united as Pangaea, later drifted apart.
- Separated populations evolved
independently → new species.
Examples: - Marsupials evolved uniquely in
Australia.
- Similar fossils found in Africa
and South America.
Conclusion: Continental drift caused geographic isolation → speciation.
17. Explain how biogeography
provides evidence for evolution.
Answer:
- Organisms in nearby geographic
regions show similarities due to shared ancestry.
Examples: - Darwin’s finches on Galápagos
Islands.
- Unique marsupials in Australia.
Inference: Distribution patterns support descent with modification and adaptive radiation.
18. What is co-evolution? Explain
with examples.
Answer:
- Definition: Two species evolve together
due to close ecological interactions.
Examples:
1.
Flowering
plants and pollinators (mutual benefit).
2.
Predator-prey
relationships (e.g., cheetah and deer).
Conclusion: Co-evolution promotes adaptation and survival for both
species.
19. Describe the differences between
convergent and divergent evolution.
Answer:
|
Basis |
Convergent Evolution |
Divergent Evolution |
|
Definition |
Unrelated species develop similar traits |
Related species develop different traits |
|
Cause |
Similar environment |
Different environment |
|
Example |
Wings of bat and bird |
Forelimbs of whale and human |
|
Result |
Analogous organs |
Homologous organs |
Conclusion: Both show how organisms adapt differently or similarly to
their environment.
20. Explain the concept of
reproductive isolation and its importance in evolution.
Answer:
- Reproductive isolation: When populations cannot
interbreed to produce fertile offspring.
Types:
1.
Prezygotic: Temporal, mechanical, behavioral
barriers.
2.
Postzygotic: Hybrid sterility (e.g., mule).
Importance:
Prevents gene flow → accumulation of genetic differences → new species
formation.
21. Describe the process of human
evolution from primates.
Answer:
- Humans evolved from primate
ancestors.
Stages:
1.
Dryopithecus (ape-like ancestor).
2.
Australopithecus (bipedal).
3.
Homo
habilis (tool
user).
4.
Homo
erectus (fire
user).
5.
Neanderthal
man (cultural).
6.
Homo
sapiens (modern).
Conclusion: Gradual increase in brain size and intelligence.
22. What is the importance of
variation in evolution?
Answer:
- Variations arise by mutation,
recombination, and gene flow.
- Provide raw material for
natural selection.
- Help species adapt to changing
environments.
- Without variation, evolution
and survival are impossible.
23. Describe the main causes of
evolution.
Answer:
1.
Mutation
2.
Recombination
3.
Gene
flow
4.
Genetic
drift
5.
Natural
selection
Each changes gene frequencies and leads to formation of new traits and species.
24. Explain the Out-of-Africa theory
of human evolution.
Answer:
- Modern humans (Homo sapiens)
originated in Africa ~200,000 years ago.
- Migrated to Asia and Europe,
replacing earlier Homo species.
- Fossil and DNA evidence
(mitochondrial DNA) supports this theory.
Conclusion: Africa is the cradle of human evolution.
25. Explain the contribution of
Miller and Urey in origin of life.
Answer:
- Simulated early Earth’s
atmosphere with CH₄, NH₃, H₂, and H₂O vapor.
- Electric discharge (lightning)
for a week.
- Obtained amino acids and
organic molecules.
Conclusion: Supported Oparin–Haldane theory of chemical evolution.
Q21. Explain the evidence of evolution from comparative anatomy and morphology.
Answer:
1.
Homologous
organs:
o Organs having the same basic
structure but different functions.
o Example: Forelimbs of humans, bats,
whales, and cheetahs.
o Indicates divergent evolution
and common ancestry.
2.
Analogous
organs:
o Organs with different structures but
similar functions.
o Example: Wings of butterfly
(membranous) and bird (bony).
o Indicates convergent evolution.
3.
Vestigial
organs:
o Non-functional remnants of
once-functional organs.
o Example: Appendix, wisdom teeth,
coccyx in humans.
o Show evolutionary remnants of our
ancestors.
Thus, comparative anatomy provides strong evidence for organic evolution.
Q22. Discuss how fossils provide
evidence for evolution.
Answer:
1.
Fossils are remains or impressions of
organisms that lived in the past.
2.
They
are preserved in sedimentary rocks in layers.
3.
Older
fossils are found in lower strata, newer ones in upper strata,
showing progressive change.
4.
Transitional
fossils like Archaeopteryx
show link between reptiles and birds.
5.
Fossil
records show the gradual evolution of species through different
geological periods.
Hence, fossils act as a historical record of evolution.
Q23. What are vestigial organs?
Explain their significance in evolution.
Answer:
1.
Vestigial
organs are non-functional remnants of structures that were functional in
ancestors.
2.
Examples:
o Appendix in humans → functional in
herbivorous ancestors for cellulose digestion.
o Nictitating membrane in humans →
functional in reptiles.
o Pelvic bones in whales → vestige of
land-dwelling ancestors.
3.
Their
presence shows descent with modification, supporting Darwin’s theory.
Significance: They indicate evolutionary relationships and evidence
of common ancestry.
Q24. Explain the concept of adaptive
radiation with suitable examples.
Answer:
1.
Adaptive
radiation = Evolution
of different species from a common ancestor in response to different
environmental conditions.
2.
Example:
o Darwin’s finches on Galápagos Islands evolved into
different species with beaks suited for eating seeds, insects, fruits, etc.
o Australian marsupials evolved into
many forms like kangaroo, koala, sugar glider, etc.
3.
It
occurs due to divergent evolution and natural selection.
Hence, adaptive radiation explains the diversity of life forms.
Q25. Compare Lamarck’s and Darwin’s
theories of evolution.
Answer:
|
Basis |
Lamarck’s Theory |
Darwin’s Theory |
|
Concept |
Inheritance of acquired characters |
Natural selection |
|
Cause |
Use and disuse of organs |
Survival of the fittest |
|
Example |
Giraffe’s long neck due to stretching |
Giraffes with longer necks survived better |
|
Transmission |
Acquired traits passed to offspring |
Only advantageous heritable traits passed |
|
Modern View |
Rejected (no evidence) |
Accepted (supported by genetics) |
Thus, Darwin’s theory remains the foundation of modern
evolutionary biology.
Q26. What is the Hardy–Weinberg
principle? Explain its significance.
Answer:
1.
Proposed
by G. H. Hardy and W. Weinberg.
2.
States
that allele frequencies in a population remain constant from generation
to generation in the absence of evolutionary forces.
3.
Expressed
as:
p2+2pq+q2=1p^2 + 2pq + q^2 = 1p2+2pq+q2=1
where
o p = frequency of dominant allele,
o q = frequency of recessive allele.
4.
Disturbance
in equilibrium occurs due to:
o Mutation, Gene flow, Genetic drift,
Natural selection, Non-random mating.
Significance: It provides a mathematical baseline for studying
evolutionary changes.
Q27. What are the main causes of
evolution?
Answer:
1.
Mutation: Sudden heritable change in DNA.
2.
Genetic
recombination:
Mixing of genes during meiosis and fertilization.
3.
Gene
flow: Movement
of genes between populations.
4.
Genetic
drift: Random
change in allele frequencies in small populations.
5.
Natural
selection: Favors
individuals with beneficial traits.
6.
Isolation: Prevents gene exchange between
populations.
These collectively bring about evolutionary changes over generations.
Q28. Describe the process of
speciation.
Answer:
1.
Speciation = Formation of new species from
pre-existing ones.
2.
Steps
involved:
o Isolation: Geographic, reproductive, or
ecological barriers separate populations.
o Variation: Mutations and recombination produce
differences.
o Natural Selection: Favors beneficial traits.
o Reproductive Isolation: Populations can no longer
interbreed.
3.
Example:
Darwin’s finches evolved into many species on different islands.
Hence, speciation explains diversity in organisms.
Q29. What is genetic drift? How does
it affect evolution?
Answer:
1.
Genetic
drift = Random
change in allele frequency in small populations.
2.
Two
major effects:
o Founder effect: Few individuals start a new
population → limited genetic variation.
o Bottleneck effect: Sudden reduction in population →
loss of diversity.
3.
Example:
Certain alleles become fixed or lost in small populations.
Impact: Leads to microevolution, loss of genetic diversity, and
sometimes speciation.
Q30. Explain the concept of natural
selection with examples.
Answer:
1.
Proposed
by Charles Darwin.
2.
Definition:
Individuals with beneficial variations survive and reproduce more.
3.
Example
1: Industrial melanism in peppered moths.
o Dark moths survived in polluted
areas.
o Light moths survived in clean areas.
4.
Example
2: Antibiotic resistance in bacteria — resistant strains survive.
Hence, natural selection drives adaptive evolution.
Q31. Explain the role of mutation in
evolution.
Answer:
1.
Mutation = Sudden change in DNA sequence.
2.
Introduces
new alleles in the gene pool.
3.
Some
mutations are advantageous, helping survival in changing environments.
4.
Example:
Sickle-cell trait provides malaria resistance.
5.
Mutation
+ natural selection = source of variation and evolution.
Thus, mutation is the raw material for evolution.
Q32. Describe the various types of
natural selection.
Answer:
1.
Stabilizing
selection:
o Favors average individuals.
o Example: Human birth weight.
2.
Directional
selection:
o Favors one extreme.
o Example: Industrial melanism.
3.
Disruptive
selection:
o Favors both extremes.
o Leads to speciation.
These mechanisms shape populations according to environmental conditions.
Q33. Explain how biogeographical
distribution supports evolution.
Answer:
1.
Different
continents have unique species adapted to their environment.
2.
Example:
o Australian marsupials vs. South
American placental mammals — similar adaptations, different ancestry.
3.
Suggests
species evolved separately after continental drift.
4.
Common
ancestry explains similarities despite geographical separation.
Thus, biogeography supports evolution through common descent.
Q34. What is molecular evidence of
evolution?
Answer:
1.
All
living organisms share same genetic code and biochemical pathways.
2.
Example:
DNA, RNA, and proteins (cytochrome c, hemoglobin) are similar across species.
3.
More
similarity = closer relationship (e.g., humans and chimpanzees share 98.8%
DNA).
4.
Shows
common ancestry and gradual divergence.
Hence, molecular biology provides quantitative proof of evolution.
Q35. Describe the evolution of man
(in brief).
Answer:
1.
Dryopithecus
& Ramapithecus:
Ape-like ancestors (~15 mya).
2.
Australopithecus: First human-like; bipedal (~4 mya).
3.
Homo
habilis: Tool
maker (~2 mya).
4.
Homo
erectus: Upright,
used fire, lived in groups (~1.5 mya).
5.
Homo
neanderthalensis:
Lived in Europe, large brain (~1,00,000 years ago).
6.
Homo
sapiens: Modern
humans, evolved in Africa (~75,000 years ago).
This shows a gradual evolution of humans from ape-like ancestors.
Q36. Describe the main postulates of Darwin’s theory of natural selection.
Answer:
Darwin’s theory (1859, Origin of Species) is based on the following
postulates:
1.
Overproduction:
o All species produce more offspring
than can survive.
2.
Variation:
o Individuals show variations in
traits (size, color, strength, etc.).
3.
Struggle
for existence:
o Limited food and space → competition
among individuals.
4.
Survival
of the fittest:
o Only those with favorable variations
survive and reproduce.
5.
Inheritance
of useful variations:
o Beneficial traits are passed on to
offspring.
6.
Formation
of new species:
o Gradual accumulation of variations →
speciation.
Hence, natural selection explains adaptive evolution and
biodiversity.
Q37. Explain the Modern Synthetic
Theory of Evolution.
Answer:
Also known as the Neo-Darwinian theory, it combines Darwin’s natural
selection with genetics.
Main factors involved:
1.
Gene
mutation: Sudden
genetic changes provide new alleles.
2.
Genetic
recombination:
Mixing of genes during meiosis and fertilization.
3.
Genetic
drift: Random
change in allele frequency.
4.
Gene
flow: Migration
introduces new genes.
5.
Natural
selection: Favors
beneficial traits.
6.
Isolation: Prevents interbreeding of
populations → speciation.
Conclusion:
Evolution = changes in gene frequencies due to these forces.
Hence, it explains microevolution and macroevolution scientifically.
Q38. What are different types of
isolation? Explain their role in speciation.
Answer:
Isolation prevents gene flow between populations, leading to speciation.
A. Prezygotic (before fertilization):
1.
Geographical
isolation: Mountains,
rivers, etc. (e.g., Darwin’s finches).
2.
Ecological
isolation: Different
habitats within same area.
3.
Temporal
isolation: Different
breeding seasons.
4.
Behavioral
isolation: Different
courtship behavior.
5.
Mechanical
isolation:
Structural differences in reproductive organs.
B. Postzygotic (after fertilization):
1.
Hybrid
inviability:
Hybrid dies early.
2.
Hybrid
sterility: Hybrid is
sterile (e.g., mule).
Thus, isolation helps populations diverge genetically → formation
of new species.
Q39. How does natural selection
bring about evolution? Explain with an example.
Answer:
Natural selection = Process where nature selects individuals with
favorable traits.
Example – Industrial Melanism:
- Before industrialization:
Light-colored Biston betularia moths survived on lichen-covered
trees.
- After industrialization: Dark
moths survived better on soot-covered trees.
- Light moths were eaten by
predators.
Mechanism:
Variation → Competition → Survival of fittest → Inheritance → Evolution.
Conclusion:
Gradually, the population adapted to its environment.
Thus, natural selection is the driving force of evolution.
Q40. What are homologous and
analogous organs? Explain with examples and their evolutionary significance.
Answer:
|
Type |
Structure |
Function |
Example |
Evolutionary significance |
|
Homologous |
Same structure, different function |
Forelimbs of whale, bat, human |
Common ancestry → Divergent evolution |
|
|
Analogous |
Different structure, same function |
Wings of bird and insect |
Different ancestry → Convergent evolution |
Significance:
- Homology → Indicates divergent
evolution.
- Analogy → Indicates convergent
evolution.
Both prove adaptive evolution and environmental influence on structure.
Q41. Explain the concept of
convergent and divergent evolution with examples.
Answer:
1.
Divergent
evolution:
o Same origin, different functions.
o Example: Forelimbs of bat (flight)
and whale (swimming).
o Leads to adaptive radiation
and homologous organs.
2.
Convergent
evolution:
o Different origin, similar functions.
o Example: Wings of butterfly and
bird.
o Results in analogous organs.
Conclusion:
Both are outcomes of natural selection in different ecological
conditions, showing how species adapt differently or similarly to environments.
Q42. Explain the concept of
Hardy–Weinberg equilibrium and factors that disturb it.
Answer:
Principle:
In a large, randomly mating population, allele frequencies remain constant if
no evolutionary forces act.
p2+2pq+q2=1p^2 + 2pq + q^2 = 1p2+2pq+q2=1
where
- p = frequency of dominant
allele
- q = frequency of recessive
allele
Disturbing factors:
1.
Mutation
2.
Migration
(gene flow)
3.
Genetic
drift
4.
Non-random
mating
5.
Natural
selection
Significance:
- Serves as a baseline to
detect evolution.
- Any deviation = population
evolving.
Q43. Discuss the role of gene flow
and genetic drift in evolution.
Answer:
1.
Gene
flow:
o Movement of alleles between
populations through migration.
o Increases genetic variation.
o Example: Migration between two
islands.
2.
Genetic
drift:
o Random change in allele frequency in
small populations.
o Can cause fixation or loss of
alleles.
o Example: Founder effect and
bottleneck effect.
Comparison:
|
Aspect |
Gene Flow |
Genetic Drift |
|
Population size |
Large |
Small |
|
Type |
Directional |
Random |
|
Effect |
Increases variation |
Reduces variation |
Both contribute to microevolution.
Q44. What is adaptive radiation? How
is it related to divergent evolution?
Answer:
1.
Definition: Evolution of different species from
a common ancestor to occupy various niches.
2.
Example:
o Darwin’s finches evolved different
beaks for different food types.
o Australian marsupials evolved into
kangaroo, koala, wombat, etc.
3.
Relation
to divergent evolution:
o Both start from a common ancestor.
o Divergent evolution is the basis
of adaptive radiation.
Hence, adaptive radiation leads to species
diversification in new habitats.
Q45. Describe the key evidences that
support organic evolution.
Answer:
1.
Palaeontological
evidence: Fossils
show gradual change over time.
2.
Comparative
anatomy:
Homologous, analogous, and vestigial organs.
3.
Embryological
evidence: Similar
embryonic stages in vertebrates.
4.
Molecular
evidence: Similar
DNA, RNA, proteins.
5.
Biogeographical
evidence:
Distribution of related species on different continents.
Together, these provide strong proof for evolution
and common ancestry.
Q46. What is the difference between
microevolution and macroevolution?
Answer:
|
Feature |
Microevolution |
Macroevolution |
|
Scale |
Small changes within species |
Large changes forming new species |
|
Time span |
Short-term |
Long-term |
|
Example |
Change in moth color |
Evolution of birds from reptiles |
|
Causes |
Mutation, recombination, selection |
Cumulative microevolution |
|
Study level |
Population genetics |
Palaeontology and taxonomy |
Conclusion:
Macroevolution is an accumulation of microevolutionary changes over
millions of years.
Q47. Explain human evolution with
the help of a flow chart.
Answer:
Flow of Evolution:
Dryopithecus → Ramapithecus →
Australopithecus → Homo habilis → Homo erectus → Homo neanderthalensis → Homo
sapiens
Highlights:
- Dryopithecus &
Ramapithecus:
Ape-like, tree-dwelling (15 mya).
- Australopithecus: Bipedal, used tools (4 mya).
- Homo habilis: “Handy man,” used stone tools
(2 mya).
- Homo erectus: Upright, used fire (1.5 mya).
- Homo neanderthalensis: Large brain, buried dead
(100,000 years ago).
- Homo sapiens: Modern humans evolved in
Africa (~75,000 years ago).
Conclusion: Evolution shows increased brain size, upright posture,
and intelligence.
Q48. Explain the differences between
human and ape skulls to show evolutionary advancement.
Answer:
|
Feature |
Ape |
Human |
|
Cranial capacity |
400–500 cc |
1400–1600 cc |
|
Forehead |
Receding |
High and vertical |
|
Face |
Protruding jaw |
Flattened face |
|
Foramen magnum |
Back of skull |
Central (upright posture) |
|
Teeth |
Large canines |
Small canines |
|
Chin |
Absent |
Present |
Inference:
Changes in skull structure reflect bipedalism, brain development, and speech
evolution.
Q49. How does comparative embryology
support evolution?
Answer:
1.
Early
embryos of vertebrates (fish, frog, bird, human) show similar features:
o Gill slits, notochord, tail.
2.
Differences
appear only in later stages.
3.
Indicates
all vertebrates have a common ancestry.
4.
Example:
Human embryos have gill slits → evidence of aquatic ancestry.
Conclusion:
Embryonic similarity supports the idea of descent with modification.
Q50. Summarize the major stages of
evolution of life on Earth.
Answer:
1.
Origin
of Earth: ~4.5 billion
years ago — hot gases, water vapor, lightning.
2.
Chemical
evolution: Formation
of simple → complex organic molecules (Oparin & Haldane).
3.
Formation
of coacervates:
First cell-like structures.
4.
Origin
of life: ~3.5
billion years ago — prokaryotes → eukaryotes.
5.
Evolution
of photosynthesis:
Released oxygen → ozone layer formation.
6.
Multicellular
life:
Diversified into plants and animals.
7.
Vertebrates
and mammals:
Evolved on land.
8.
Humans: Appeared ~75,000 years ago.
Conclusion:
Life evolved through chemical → biological → social evolution over
billions of years.
