🧬 Heredity | Evolution by Natural Selection
प्राकृतिक चयन द्वारा विकास | Evolution through Natural Selection
Class 10 Science | CBSE + Foundation + Competitive Level
🌿 Heredity | Evolution by Natural Selection
1. Introduction | परिचय
Natural Selection / प्राकृतिक चयन एक evolutionary process है जिसमें किसी population में मौजूद heritable variations के कारण कुछ individuals अपने environment में दूसरों की तुलना में बेहतर survive और reproduce कर पाते हैं।
ऐसे advantageous heritable traits अगली generations में अधिक common हो सकते हैं।
इसी प्रक्रिया से populations समय के साथ environmental conditions के अनुसार adapt हो सकती हैं।
ऐसे advantageous heritable traits अगली generations में अधिक common हो सकते हैं।
इसी प्रक्रिया से populations समय के साथ environmental conditions के अनुसार adapt हो सकती हैं।
Important: Natural selection यह नहीं कहता कि organisms अपनी आवश्यकता के अनुसार traits स्वयं बना लेते हैं। Variations पहले से population में मौजूद हो सकते हैं और environment कुछ variants के survival/reproduction को favour कर सकता है।
2. Charles Darwin and Natural Selection
Charles Darwin ने natural selection द्वारा evolution का महत्वपूर्ण scientific explanation दिया।
Darwin ने विभिन्न organisms और उनके variations का अध्ययन किया तथा बताया कि nature में limited resources के कारण organisms के बीच competition होता है।
जो heritable variations survival और reproduction में advantage देते हैं, वे generations में अधिक common हो सकते हैं।
Darwin ने विभिन्न organisms और उनके variations का अध्ययन किया तथा बताया कि nature में limited resources के कारण organisms के बीच competition होता है।
जो heritable variations survival और reproduction में advantage देते हैं, वे generations में अधिक common हो सकते हैं।
3. Darwin's Basic Idea | Darwin का मूल विचार
Variation
भिन्नता
भिन्नता
→
Competition
प्रतिस्पर्धा
प्रतिस्पर्धा
→
Differential Survival
अलग-अलग survival
अलग-अलग survival
→
Reproduction
प्रजनन
प्रजनन
→
More Advantageous Traits
लाभकारी traits ↑
लाभकारी traits ↑
4. Variation | विविधता
एक population के individuals बिल्कुल identical नहीं होते। उनके characteristics में differences पाए जा सकते हैं।
इन differences को variations कहते हैं।
Variations के sources में शामिल हो सकते हैं:
Variations के sources में शामिल हो सकते हैं:
- DNA copying में छोटे changes
- Mutation
- Sexual reproduction में genetic recombination
- Gene flow जैसी population processes
5. Heritable Variation vs Acquired Change
| Heritable Variation | Acquired Change |
|---|---|
| Genetic basis हो सकता है | जीवनकाल में environment/training से develop हो सकता है |
| Offspring तक transmit हो सकता है | सामान्यतः inherited नहीं होता |
| Natural selection पर प्रभाव डाल सकता है | अपने आप inherited नहीं होता |
| Example: inherited variation in beak shape | Exercise से developed muscles |
6. Struggle for Existence | अस्तित्व के लिए संघर्ष
Natural populations में resources जैसे food, water, space और mates सीमित हो सकते हैं।
जब population में individuals अधिक offspring produce करते हैं और resources limited होते हैं, तो competition या struggle for existence उत्पन्न होता है।
Key idea:
सभी individuals समान रूप से survive और reproduce नहीं करते। Environmental conditions कुछ variations को favour कर सकती हैं।
7. Survival of the Fittest
“Fittest” का अर्थ सबसे मजबूत या सबसे बड़ा organism नहीं है।
Biology में fitness का अर्थ है—किसी particular environment में survive करके सफलतापूर्वक reproduce करने की relative ability।
इसलिए:
Fittest = Best adapted for a particular environment
इसलिए:
Fittest = Best adapted for a particular environment
8. Natural Selection – Animated Process
🐇 Natural Selection in a Population
9. Step-by-Step Mechanism of Natural Selection
Step 1 – Variation:
Population में different variations मौजूद होते हैं।
Step 2 – Heritability:
कुछ variations genetic/heritable होते हैं।
Step 3 – Environmental Pressure:
Environment survival और reproduction को प्रभावित करता है।
Step 4 – Differential Survival:
कुछ individuals दूसरों की तुलना में अधिक successfully survive करते हैं।
Step 5 – Differential Reproduction:
Better-adapted individuals अधिक offspring छोड़ सकते हैं।
Step 6 – Change in Population:
Generations के दौरान advantageous heritable traits population में अधिक common हो सकते हैं।
Population में different variations मौजूद होते हैं।
Step 2 – Heritability:
कुछ variations genetic/heritable होते हैं।
Step 3 – Environmental Pressure:
Environment survival और reproduction को प्रभावित करता है।
Step 4 – Differential Survival:
कुछ individuals दूसरों की तुलना में अधिक successfully survive करते हैं।
Step 5 – Differential Reproduction:
Better-adapted individuals अधिक offspring छोड़ सकते हैं।
Step 6 – Change in Population:
Generations के दौरान advantageous heritable traits population में अधिक common हो सकते हैं।
10. Peppered Moth Example | Peppered Moth का उदाहरण
Peppered moth के उदाहरण का उपयोग natural selection समझाने के लिए किया जाता है।
Industrial pollution वाले क्षेत्रों में पेड़ों की bark का रंग dark हो गया था। ऐसे वातावरण में darker moths को predators से camouflage advantage मिल सकता था। जब pollution कम हुआ और tree trunks comparatively lighter हुए, तो lighter moths को camouflage advantage मिल सकता था।
यह example दिखाता है कि environmental conditions बदलने पर selection pressure भी बदल सकता है।
Industrial pollution वाले क्षेत्रों में पेड़ों की bark का रंग dark हो गया था। ऐसे वातावरण में darker moths को predators से camouflage advantage मिल सकता था। जब pollution कम हुआ और tree trunks comparatively lighter हुए, तो lighter moths को camouflage advantage मिल सकता था।
यह example दिखाता है कि environmental conditions बदलने पर selection pressure भी बदल सकता है।
Important: Moths ने environment की आवश्यकता के अनुसार अपना रंग consciously नहीं बदला। Population में variation मौजूद था और different environments में survival rates अलग हो सकते थे।
11. Antibiotic Resistance | Antibiotic Resistance और Natural Selection
Bacterial population में genetic variations हो सकते हैं। यदि कुछ bacteria में antibiotic resistance प्रदान करने वाला heritable variation मौजूद है, तो antibiotic treatment susceptible bacteria की संख्या कम कर सकता है।
Resistant bacteria survive करके reproduce कर सकते हैं।
यदि antibiotic का उपयोग selection pressure बनाता है, तो generations में resistant bacteria का proportion बढ़ सकता है।
यदि antibiotic का उपयोग selection pressure बनाता है, तो generations में resistant bacteria का proportion बढ़ सकता है।
Important concept:
Antibiotic resistance का बढ़ना bacteria द्वारा “जरूरत के कारण” resistance पैदा करना नहीं है। Existing genetic variation और selection इसके प्रमुख evolutionary mechanisms में हैं।
12. Allele Frequency and Natural Selection
Allele frequency किसी population के gene pool में किसी particular allele का relative frequency है।
Natural selection के कारण advantageous allele से जुड़े traits अधिक reproductive success दे सकते हैं। परिणामस्वरूप generations में उस allele की frequency बढ़ सकती है।
Allele Frequency = Number of copies of an allele ÷ Total copies of all alleles at that locus
उदाहरण:
यदि किसी population में किसी gene की कुल 100 allele copies हैं और allele A की 30 copies हैं, तो:
Frequency of A = 30 ÷ 100 = 0.30 = 30%
13. Natural Selection and Population Change
Natural selection individuals पर कार्य करता है, लेकिन उसका evolutionary effect population में generations के दौरान दिखाई देता है।
Individual organism अपने जीवनकाल में evolutionary population change का प्रतिनिधित्व नहीं करता। यदि heritable variants की reproductive success अलग-अलग हो, तो population की genetic composition समय के साथ बदल सकती है।
Individual organism अपने जीवनकाल में evolutionary population change का प्रतिनिधित्व नहीं करता। यदि heritable variants की reproductive success अलग-अलग हो, तो population की genetic composition समय के साथ बदल सकती है।
Interactive Concept Visualization:
नीचे beneficial allele के generations में बढ़ने की प्रक्रिया को explore किया जा सकता है।
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नीचे beneficial allele के generations में बढ़ने की प्रक्रिया को explore किया जा सकता है।
14. Natural Selection vs Artificial Selection
| Natural Selection | Artificial Selection |
|---|---|
| Environment/natural conditions selection pressure देते हैं | Humans desired traits के लिए organisms select करते हैं |
| Natural populations में होता है | Breeding programmes में commonly used |
| Example: camouflage advantage | Dogs/crops में selected traits |
| Human intention आवश्यक नहीं | Human choice प्रमुख factor |
15. Natural Selection and Adaptation
Adaptation किसी population में ऐसा heritable characteristic या characteristic combination हो सकता है जो particular environment में survival या reproduction को improve करता है।
यदि selection किसी advantageous heritable trait को favour करती है, तो वह trait generations में अधिक common हो सकता है।
यदि selection किसी advantageous heritable trait को favour करती है, तो वह trait generations में अधिक common हो सकता है।
16. Natural Selection is Not Random
Variation उत्पन्न होने की processes जैसे mutation सामान्यतः organism की future need को देखकर directed नहीं होतीं।
लेकिन selection random नहीं है—environmental conditions कुछ heritable variants को दूसरों की तुलना में अधिक reproductive success दे सकती हैं।
17. Important Examples
| Example | Natural Selection Concept |
|---|---|
| Peppered moth | Camouflage and changing environment |
| Antibiotic-resistant bacteria | Resistance and selection pressure |
| Darwin's finches | Adaptive radiation and selection |
| Pesticide-resistant insects | Selection for resistant variants |
18. Natural Selection and Darwin's Finches
Darwin's finches की populations में beak characteristics में variation पाया गया।
अलग-अलग food resources और ecological conditions के कारण अलग beak forms अलग परिस्थितियों में अधिक advantageous हो सकते थे।
कई generations में natural selection और divergence ने अलग populations के diversification में योगदान दिया।
19. Natural Selection and Speciation
यदि populations अलग हो जाएँ और उनके बीच gene flow बहुत कम या बंद हो जाए, तो अलग environments में natural selection अलग traits को favour कर सकती है।
समय के साथ genetic differences बढ़ सकते हैं।
यदि reproductive isolation स्थापित हो जाए, तो नई species के formation में योगदान हो सकता है।
Exam Point:
Natural selection अकेले हर situation में नई species बनाने के लिए पर्याप्त नहीं होती। Speciation में reproductive isolation और genetic divergence महत्वपूर्ण हैं।
20. Evolutionary Tree and Natural Selection
21. 30 MCQs | Multiple Choice Questions
Q1. Natural selection acts primarily on:
A. Phenotypic variations affecting survival/reproduction
B. Only fossils
C. Rocks
D. Individual chromosomes in isolation
Answer: A
Q2. Evolutionary change through natural selection is observed over generations mainly in:
A. A single individual
B. A population
C. A single organ
D. A single cell only
Answer: B
Q3. A variation important for natural selection must generally be:
A. Always harmful
B. Acquired through exercise
C. Heritable to influence evolution across generations
D. Identical in every organism
Answer: C
Q4. Darwin is most closely associated with:
A. Cell theory
B. Germ theory
C. Chromosome theory
D. Natural selection
Answer: D
Q5. “Survival of the fittest” means survival of organisms that:
A. Are best adapted to their environment
B. Are always physically strongest
C. Are largest
D. Live longest regardless of reproduction
Answer: A
Q6. Which process can generate new genetic variation?
A. Digestion
B. Mutation
C. Respiration
D. Excretion
Answer: B
Q7. Natural selection generally changes:
A. Rocks
B. Climate directly
C. Frequencies of heritable variants in populations
D. The age of individuals
Answer: C
Q8. Antibiotic resistance in bacteria is an example of:
A. Digestion
B. Artificial fertilisation
C. Photosynthesis
D. Natural selection
Answer: D
Q9. Peppered moths are commonly used to explain:
A. Natural selection and camouflage
B. Binary fission
C. Photosynthesis
D. Respiration
Answer: A
Q10. A beneficial allele may increase in frequency when:
A. It prevents reproduction
B. It provides a reproductive advantage
C. It is always recessive
D. It occurs only in fossils
Answer: B
Q11. Natural selection is:
A. Completely independent of environment
B. A process that creates traits according to need
C. Differential reproductive success associated with heritable variation
D. A process occurring only in humans
Answer: C
Q12. Which statement is correct?
A. Individuals evolve because they need to
B. Acquired traits are always inherited
C. Evolution occurs within one individual's lifetime
D. Populations can change genetically over generations
Answer: D
Q13. Allele frequency refers to:
A. Relative frequency of an allele in a population
B. Number of organs in an organism
C. Body weight of an individual
D. Number of fossils
Answer: A
Q14. If an advantageous allele becomes more common over generations, this is:
A. Extinction of all variation
B. Evolutionary change in the population
C. Digestion
D. Growth of an individual
Answer: B
Q15. Which factor can act as a selection pressure?
A. Food availability
B. Predation
C. Disease
D. All of the above
Answer: D
Q16. Natural selection does NOT necessarily:
A. Favour some heritable variants
B. Depend on environmental conditions
C. Make every organism stronger or more complex
D. Affect reproductive success
Answer: C
Q17. Darwin's finches illustrate:
A. Adaptive radiation
B. Photosynthesis
C. Binary fission
D. Tissue culture
Answer: A
Q18. A trait favoured in one environment may:
A. Always be favoured everywhere
B. Be less advantageous in another environment
C. Never be inherited
D. Stop DNA replication
Answer: B
Q19. Which is an example of artificial selection?
A. Predator avoiding camouflaged prey
B. Antibiotic resistance
C. Humans selecting dogs with desired traits for breeding
D. Natural variation in moths
Answer: C
Q20. Reproductive isolation is especially important in:
A. Digestion
B. Photosynthesis
C. Respiration
D. Speciation
Answer: D
Q21. Which statement about mutation is correct?
A. It can introduce genetic variation
B. It always produces beneficial traits
C. It occurs only when organisms need it
D. It always causes disease
Answer: A
Q22. Natural selection can result in:
A. Loss of all variation immediately
B. Increased frequency of advantageous heritable traits
C. No change in populations
D. Creation of fossils directly
Answer: B
Q23. Which phrase best describes fitness?
A. Physical strength only
B. Body size only
C. Relative reproductive success in a given environment
D. Lifespan only
Answer: C
Q24. Environmental change can:
A. Change which variants are advantageous
B. Stop all reproduction permanently
C. Remove DNA from all organisms
D. Make evolution impossible
Answer: A
Q25. Which is NOT required for natural selection?
A. Variation
B. Heritability
C. Differential reproductive success
D. Conscious intention by organisms
Answer: D
Q26. Selection pressure means:
A. Environmental factor influencing survival/reproduction
B. Blood pressure
C. Atmospheric pressure only
D. Pressure inside a cell
Answer: A
Q27. Evolution through natural selection is best described as:
A. Need-based change in individuals
B. Change in population characteristics across generations
C. Change in body size during growth
D. Acquired skill development
Answer: B
Q28. Antibiotic-resistant bacteria become common mainly because:
A. Antibiotics intentionally create resistance in every bacterium
B. Bacteria consciously adapt
C. Resistant variants survive and reproduce more under selection pressure
D. All bacteria are naturally resistant
Answer: C
Q29. Natural selection can contribute to speciation when:
A. Populations remain completely identical
B. Genetic differences accumulate with reproductive isolation
C. All individuals have the same genotype
D. No variation exists
Answer: B
Q30. Which sequence best represents natural selection?
A. Variation → selection → differential reproduction → population change
B. Need → conscious mutation → identical offspring
C. Environment → no variation → evolution
D. Growth → exercise → inherited muscles
Answer: A
22. 30 Subjective Questions with Answers
2 Marks
Q1. What is natural selection?
Natural selection is the process in which heritable variations that improve survival or reproductive success become more common in a population over generations.
2 Marks
Q2. What is variation?
Variation means differences in characteristics among individuals of the same population or species.
2 Marks
Q3. Who proposed natural selection as an explanation of evolution?
Charles Darwin is strongly associated with the theory of evolution by natural selection. Alfred Russel Wallace independently developed a similar idea.
2 Marks
Q4. Define fitness in evolutionary biology.
Fitness refers to an organism's relative ability to survive and reproduce successfully in a particular environment.
2 Marks
Q5. What is allele frequency?
Allele frequency is the relative proportion of a particular allele among all copies of alleles at that gene locus in a population.
3 Marks
Q6. Explain the role of variation in natural selection.
Variation provides differences among individuals. If some variations are heritable and provide a survival or reproductive advantage, natural selection can increase their frequency over generations.
3 Marks
Q7. Why is heredity important in natural selection?
For a trait to contribute to evolutionary change, its genetic basis must be capable of being transmitted to offspring. Heritable advantageous traits can therefore become more common over generations.
3 Marks
Q8. What is meant by survival of the fittest?
It means that organisms better adapted to a particular environment may have greater survival and reproductive success. “Fittest” does not simply mean physically strongest.
3 Marks
Q9. Give three examples of natural selection.
Examples include antibiotic resistance in bacteria, pesticide resistance in insects and camouflage-related selection such as the classic peppered moth example.
3 Marks
Q10. Why do acquired traits generally not contribute directly to inherited evolution?
Acquired traits such as improved muscles through exercise usually do not change the DNA of reproductive cells in a way that transmits the acquired characteristic to offspring. Therefore, they are generally not inherited.
4 Marks
Q11. Explain natural selection in four steps.
- Variation exists in a population.
- Some variations are heritable.
- Environmental conditions cause differential survival and reproduction.
- Advantageous heritable traits can become more common over generations.
4 Marks
Q12. Explain the role of environmental pressure in natural selection.
Environmental factors such as predators, food availability, climate and disease can influence survival and reproduction. Individuals possessing suitable heritable variations may leave more offspring, causing those traits to increase in frequency.
4 Marks
Q13. Explain antibiotic resistance using natural selection.
A bacterial population may contain genetic variation, including resistant variants. Antibiotic treatment kills or inhibits susceptible bacteria more effectively. Resistant bacteria survive and reproduce, so resistance can become more common in later generations.
4 Marks
Q14. What is the difference between natural and artificial selection?
Natural selection is driven by environmental conditions and differential reproductive success. Artificial selection is directed by humans, who choose organisms with desired characteristics for breeding.
4 Marks
Q15. Explain why natural selection does not mean that organisms change because they need to.
Variations arise without organisms consciously deciding which variation they need. Environmental conditions select among existing heritable variations. Individuals with advantageous variations may leave more offspring.
5 Marks
Q16. Explain Darwin's theory of natural selection.
Darwin's theory is based on variation, overproduction, struggle for existence, differential survival and reproduction, and inheritance of favourable variations. Individuals with advantageous heritable variations are more likely to survive and reproduce. Over many generations, favourable traits can become more common in the population.
5 Marks
Q17. Explain the peppered moth example.
Peppered moth populations contained colour variations. When tree trunks became darker in polluted areas, darker moths could be better camouflaged from predators. When pollution decreased and trunks became lighter, lighter moths could have an advantage. This demonstrates environment-dependent natural selection.
5 Marks
Q18. Explain the relationship between variation and adaptation.
Variation provides differences among individuals. When a heritable variation improves survival or reproduction in a particular environment, natural selection may favour it. Over generations, such traits can become more common and contribute to adaptation of the population.
5 Marks
Q19. Explain how allele frequency can change through natural selection.
Suppose an allele is associated with a heritable trait that improves reproductive success. Individuals carrying it may leave more offspring. As their offspring inherit the allele, its relative frequency in the population can increase across generations.
5 Marks
Q20. Explain why natural selection is not the same as conscious choice.
Natural selection is an outcome of differences in survival and reproduction caused by environmental conditions. Organisms do not consciously choose beneficial mutations. Existing heritable variations that increase reproductive success may become more common over generations.
6 Marks
Q21. Explain evolution by natural selection in detail.
Evolution by natural selection begins with variation within a population. Some variations are heritable. Organisms compete for limited resources and face environmental pressures. Individuals with advantageous heritable variations may survive and reproduce more successfully. Their offspring inherit these traits. Across many generations, the frequency of advantageous variants can increase, causing population-level evolutionary change.
6 Marks
Q22. Explain natural selection using antibiotic resistance.
Bacterial populations contain genetic variation. Some bacteria may already possess mutations or genetic variants that provide antibiotic resistance. When an antibiotic is applied, susceptible bacteria are eliminated more effectively while resistant bacteria survive. Resistant bacteria reproduce and pass the resistance-associated genes to offspring. Repeated selection can increase the proportion of resistant bacteria.
6 Marks
Q23. Explain the relationship between natural selection and adaptation.
Adaptation refers to heritable characteristics that improve fitness in a particular environment. Natural selection favours heritable variations that provide an advantage. Over generations, these variants may become more common. Thus natural selection can produce population adaptations.
6 Marks
Q24. Explain the role of genetic variation in evolution.
Genetic variation results from processes such as mutation and recombination. It produces differences among individuals. Natural selection acts on phenotypic differences associated with heritable genetic variation. If certain variants increase reproductive success, their frequencies may increase over generations.
6 Marks
Q25. Explain Darwin's finches as an example of natural selection and adaptive radiation.
Darwin's finches descended from ancestral populations and showed variation in beak characteristics. Different islands and food resources created different selection pressures. Birds with beaks suited to particular food sources could have greater reproductive success. Over generations, populations diverged and became adapted to different niches, illustrating adaptive radiation.
6 Marks
Q26. Explain why evolution occurs at population level rather than individual level.
An individual has a fixed genetic constitution during its lifetime except for somatic changes and mutations. Natural selection changes the relative reproductive contribution of different variants. When these frequency changes accumulate across generations, the genetic composition of the population changes. This is evolution.
6 Marks
Q27. Explain the meaning of “fittest” in natural selection.
Fitness is environment-dependent. It refers to relative reproductive success rather than physical strength alone. An organism that survives and produces more viable offspring under particular environmental conditions has greater fitness in that environment.
6 Marks
Q28. How can natural selection contribute to speciation?
When populations become geographically or reproductively isolated, they may experience different environments and selection pressures. Heritable differences can accumulate through generations. If reproductive isolation becomes strong enough, the populations may become distinct species.
6 Marks
Q29. Differentiate between mutation, variation and natural selection.
| Term | Meaning |
|---|---|
| Mutation | A change in genetic material that can introduce variation. |
| Variation | Differences in traits/genetic characteristics among individuals. |
| Natural selection | Differential survival and reproduction associated with heritable variation. |
6 Marks
Q30. “Natural selection is a population-level evolutionary process.” Explain.
Natural selection acts through differences in survival and reproduction among individuals, but its long-term result is a change in the frequency of heritable variants in the population. If advantageous variants produce more offspring, those variants may increase in frequency over generations. Therefore, evolutionary change is observed at population level.
23. Assertion–Reason Questions
Q1.
Assertion: Natural selection can increase the frequency of advantageous heritable traits.
Reason: Individuals with advantageous traits may have greater reproductive success.
Reason: Individuals with advantageous traits may have greater reproductive success.
Answer: Both A and R are true, and R correctly explains A.
Q2.
Assertion: Organisms develop useful traits because they consciously need them.
Reason: Natural selection acts on heritable variation present in populations.
Reason: Natural selection acts on heritable variation present in populations.
Answer: Assertion is false, Reason is true.
Q3.
Assertion: Antibiotic resistance can increase in bacterial populations.
Reason: Resistant variants may survive antibiotic treatment and reproduce.
Reason: Resistant variants may survive antibiotic treatment and reproduce.
Answer: Both A and R are true, and R correctly explains A.
Q4.
Assertion: Evolution occurs at the population level over generations.
Reason: Natural selection can change the frequency of heritable variants in populations.
Reason: Natural selection can change the frequency of heritable variants in populations.
Answer: Both A and R are true, and R correctly explains A.
Q5.
Assertion: The fittest organism is always the strongest organism.
Reason: Fitness means relative reproductive success in a particular environment.
Reason: Fitness means relative reproductive success in a particular environment.
Answer: Assertion is false, Reason is true.
24. HOTS / Competency-Based Questions
HOTS 1.
A bacterial population contains 1% resistant bacteria before antibiotic treatment. After several generations of antibiotic exposure, resistant bacteria form 70% of the population. Explain.
The original population already contained variation. Antibiotic exposure created a selection pressure under which resistant bacteria had greater survival and reproduction. Their proportion therefore increased across generations.
HOTS 2.
If a trait is acquired through exercise but has no genetic basis, why is it unlikely to become an inherited evolutionary trait?
Because the acquired change generally does not alter the genetic information transmitted through reproductive cells. Therefore it is not normally inherited by offspring.
HOTS 3.
A dark-coloured moth has greater survival on dark tree bark but lower survival on light bark. What does this demonstrate?
It demonstrates that fitness is environment-dependent and that natural selection can favour different phenotypes under different environmental conditions.
HOTS 4.
Why can an adaptation that is advantageous today become disadvantageous after environmental change?
Fitness depends on environmental conditions. If the environment changes, the trait may no longer provide the same survival or reproductive advantage, and another variant may become favoured.
HOTS 5.
Why does natural selection not necessarily produce more complex organisms?
Natural selection favours traits that improve fitness in a particular environment, not traits that make organisms universally more complex. Simple traits can be highly advantageous when suited to an environment.
25. Important Diagram Labelling
Natural Selection Diagram:
Variation Environmental Pressure Survival Reproduction Inheritance Population Change
Variation Environmental Pressure Survival Reproduction Inheritance Population Change
Evolutionary Tree:
Common Ancestor Branch Point Branch Descendant Population Divergence
Common Ancestor Branch Point Branch Descendant Population Divergence
26. CBSE Golden Points | परीक्षा के लिए महत्वपूर्ण तथ्य
- Natural selection is a mechanism of evolution.
- Variation is essential for natural selection.
- Only heritable variation can contribute directly to evolutionary change across generations.
- Natural selection depends on environmental conditions.
- Fitness means relative reproductive success, not simply physical strength.
- Evolution occurs at the population level over generations.
- Advantageous heritable traits may become more common in a population.
- Natural selection does not create traits according to an organism's conscious need.
- Mutation can introduce new genetic variation.
- Sexual reproduction can generate variation through recombination.
- Peppered moths are a classic example used to explain natural selection.
- Antibiotic resistance illustrates selection acting on bacterial variation.
- Darwin's finches are associated with adaptive radiation.
- Environmental change can alter which traits are advantageous.
- Natural selection is not goal-directed.
- Evolution does not necessarily mean increasing complexity.
- Natural selection can contribute to speciation when populations diverge and reproductive isolation develops.
27. Memory Trick | याद रखने की ट्रिक
🌿 Natural Selection = “V-C-S-R-I”
V = VariationC = Competition
S = Selection / Differential Survival
R = Reproduction
I = Inheritance & Increase of advantageous traits
Easy Formula:
Variation → Environment → Survival → Reproduction → Population Change
Antibiotic Resistance:
Variation → Antibiotic → Susceptible ↓ → Resistant survives → Resistant offspring ↑
Homologous = Common ancestry
Natural Selection = Differential reproductive success
Adaptation = Heritable advantage in a particular environment
28. One-Line Revision | एक नजर में पूरा Topic
Variation → Population में differences
Heritable variation → Offspring तक genetic information जा सकती है
Selection pressure → Environment survival/reproduction को प्रभावित करता है
Fitness → Relative reproductive success
Natural selection → Advantageous heritable variants की reproductive success अधिक हो सकती है
Adaptation → Environment में fitness बढ़ाने वाली heritable characteristics
Allele frequency → Population में allele का relative proportion
Evolution → Generations के दौरान population की heritable characteristics/frequencies में परिवर्तन
Speciation → Genetic divergence + reproductive isolation से नई species formation में योगदान
Heritable variation → Offspring तक genetic information जा सकती है
Selection pressure → Environment survival/reproduction को प्रभावित करता है
Fitness → Relative reproductive success
Natural selection → Advantageous heritable variants की reproductive success अधिक हो सकती है
Adaptation → Environment में fitness बढ़ाने वाली heritable characteristics
Allele frequency → Population में allele का relative proportion
Evolution → Generations के दौरान population की heritable characteristics/frequencies में परिवर्तन
Speciation → Genetic divergence + reproductive isolation से नई species formation में योगदान
29. Final Summary | अंतिम सारांश
Evolution by natural selection को समझने के लिए सबसे महत्वपूर्ण concepts हैं—variation, heredity, environmental pressure, differential survival, differential reproduction और population change।
Population में variations मौजूद होते हैं। इनमें से कुछ heritable होते हैं। Environment कुछ variations को survival और reproduction के लिए अधिक advantageous बना सकता है। ऐसे individuals अधिक offspring छोड़ सकते हैं और उनके advantageous traits अगली generations में अधिक common हो सकते हैं।
इस प्रकार natural selection populations को समय के साथ बदल सकता है और adaptation तथा, अन्य evolutionary processes के साथ, speciation में योगदान कर सकता है।
सबसे महत्वपूर्ण बात: Organisms अपनी आवश्यकता के अनुसार consciously evolve नहीं करते। Evolution generations में heritable variation और differential reproductive success के परिणामस्वरूप population level पर होता है।
Population में variations मौजूद होते हैं। इनमें से कुछ heritable होते हैं। Environment कुछ variations को survival और reproduction के लिए अधिक advantageous बना सकता है। ऐसे individuals अधिक offspring छोड़ सकते हैं और उनके advantageous traits अगली generations में अधिक common हो सकते हैं।
इस प्रकार natural selection populations को समय के साथ बदल सकता है और adaptation तथा, अन्य evolutionary processes के साथ, speciation में योगदान कर सकता है।
सबसे महत्वपूर्ण बात: Organisms अपनी आवश्यकता के अनुसार consciously evolve नहीं करते। Evolution generations में heritable variation और differential reproductive success के परिणामस्वरूप population level पर होता है।
🧬 Heredity | Evolution by Natural Selection
Class 10 Science | CBSE + Foundation + Competitive Preparation
Study • Understand • Practice • Revise
Class 10 Science | CBSE + Foundation + Competitive Preparation
Study • Understand • Practice • Revise
