NCERT Solutions Class 12 Biology Chapter 7 Evolution
Complete Solutions for Questions 1-41 - CBSE Class 12 Biology
1
Question
Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.
Answer
Antibiotic resistance in bacteria illustrates Darwinian selection theory perfectly. When bacterial populations are exposed to antibiotics, the environment selects organisms with favorable variations. Sensitive bacteria cannot tolerate the antibiotic and die due to the adverse environment, while some bacteria that developed mutations become resistant to the particular antibiotic and survive. These resistant bacteria survive and multiply quickly compared to sensitive bacteria. As a result, the whole population is regained by multiplication of the resistant variety, and antibiotic-resistant genes become widespread in the bacterial population through natural selection.
2
Question
Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.
Answer
A recent fossil discovery revealed a small terrestrial dinosaur with feathers covering its limbs and body. This finding established that feathers evolved earlier than wings and may have initially functioned as thermoregulators to face adverse environmental conditions. These newly developed feathers earlier helped in gliding and then evolved for flying. This discovery provides important evidence for the evolutionary transition from terrestrial to aerial locomotion in dinosaurs.
3
Question
Attempt giving a clear definition of the term species.
Answer
A species can be defined as a group of reproductively isolated populations that can interbreed among each other under natural conditions to produce fertile offspring. Members of the same species share similar morphological characteristics and genetic makeup, and they are reproductively isolated from other such groups.
4
Question
Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)
Answer
Components of human evolution include several key changes:
| Human Ancestors | Time Period | Brain Capacity | Key Features |
|---|---|---|---|
| Dryopithecus/Ramapithecus | 15 mya | Large brain | Ape-like, hairy, walked like gorillas |
| Australopithecus | 2 mya | 400-600 cc | 4 feet tall, walked upright, used stone weapons |
| Homo habilis | 2 mya | 650-800 cc | First human-like being, did not eat meat |
| Homo erectus | 1.5 mya | 900 cc | Started eating meat |
| Homo sapiens neanderthalensis | 100,000-40,000 years ago | 1400 cc | Used hides, buried dead |
| Homo sapiens (Modern man) | 75,000-10,000 years ago | 1350-1450 cc | Cave art, agriculture, civilization |
Key evolutionary milestones: 18,000 years ago - cave art developed, 10,000 years ago - agriculture started
5
Question
Find out through internet and popular science articles whether animals other than man has self-consciousness.
Answer
Yes, many animals other than humans possess self-consciousness. Dolphins and chimpanzees are considered highly intelligent and have demonstrated self-awareness. They have a sense of self and can recognize themselves and others among their species. These animals communicate with each other through complex methods including whistles, tail-slapping, and various body movements, indicating advanced cognitive abilities and social awareness.
6
Question
List 10 modern-day animals and using the internet resources link it to a corresponding ancient fossil. Name both.
Answer
| S.No. | Modern Animal | Ancient Fossil |
|---|---|---|
| 1 | Man | Homo sapiens neanderthalensis |
| 2 | Chimpanzee | Dryopithecus |
| 3 | Gorilla | Dryopithecus |
| 4 | Orangutan | Dryopithecus |
| 5 | Gibbon | Propliopithecus |
| 6 | Nautilus | Gypceros |
| 7 | Octopus | Belemnite |
| 8 | Elephant | Stegolophodon |
| 9 | Camel | Procamelus |
| 10 | Horse | Pliohippus |
7
Question
Practice drawing various animals and plants.
Answer
This is a practical instruction question. Students should practice drawing labeled diagrams of various animals and plants from their textbook. This helps in understanding morphological features, anatomical structures, and evolutionary relationships. Focus on drawing accurate proportions, proper labeling, and clear identification of key evolutionary features that distinguish different species.
8
Question
Describe one example of adaptive radiation.
Answer
An excellent example of adaptive radiation is Darwin's finches on the Galapagos Islands. These finches evolved from a common ancestor but with evolution, they modified into different types according to their food habits. Different species developed various beak shapes and sizes adapted for different food sources - some for cracking seeds, others for nectar feeding, insect catching, or fruit eating. This diversification from a single ancestral species into multiple species with different ecological niches demonstrates adaptive radiation.
9
Question
Using various resources such as your school library or the internet and discussions with your teacher, trace the evolutionary stages of any one animal, say horse.
Answer
The evolutionary stages of the horse show a clear progression:
10
Question
Can we call human evolution as adaptive radiation?
Answer
No, human evolution cannot be called adaptive radiation because the parent species of Homo sapiens evolved through progressive evolution from Homo habilis to Homo erectus lineage in a linear fashion. Adaptive radiation involves diversification of a single species into multiple species to fill different ecological niches, whereas human evolution shows a linear progression with gradual changes over time rather than diversification into multiple species.
11
Question (MCQ)
Stabilising selection favours:
- (a) only one extreme form of a trait
- (b) both the extreme forms of a trait
- (c) intermediate form of a trait
- (d) none of these
Answer
Answer: (c) intermediate form of a trait
Stabilising selection favors individuals with intermediate traits and selects against extreme variations. This type of selection reduces genetic variation and maintains the status quo of a population by favoring the average phenotype.
12
Question (MCQ)
The most accepted line of descent in human evolution is:
- (a) Australopithecus → Ramapithecus → Homo sapiens → Homo habilis
- (b) Homo erectus → Homo habilis → Homo sapiens
- (c) Ramapithecus → Homo habilis → Homo erectus → Homo sapiens
- (d) Australopithecus → Ramapithecus → Homo erectus → Homo habilis → Homo sapiens
Answer
Answer: (c) Ramapithecus → Homo habilis → Homo erectus → Homo sapiens
This represents the most accepted chronological sequence of human evolution based on fossil evidence and anatomical studies.
13
Question (MCQ)
Disruptive selection favours:
- (a) only one extreme form of a trait
- (b) both the extreme forms of a trait
- (c) intermediate form of a trait
- (d) none of these
Answer
Answer: (b) both the extreme forms of a trait
Disruptive selection favors individuals at both extremes of a trait distribution and selects against intermediate forms, potentially leading to the formation of two distinct groups.
14
Question (MCQ)
Thorn of Bougainvillea and tendril of Cucurbita are examples of:
- (a) vestigial organs
- (b) retrogressive evolution
- (c) analogous organs
- (d) homologous organs
Answer
Answer: (d) homologous organs
Both thorns of Bougainvillea and tendrils of Cucurbita are modified stems with similar origin but different functions, making them homologous organs showing divergent evolution.
15
Question (MCQ)
The theory of spontaneous generation stated that:
- (a) life arose from living forms only
- (b) life can arise from both living and non-living
- (c) life can arise from non-living things only
- (d) life arises spontaneously, neither from living nor from the non-living
Answer
Answer: (c) life can arise from non-living things only
The theory of spontaneous generation proposed that living organisms could arise spontaneously from non-living matter under certain conditions.
16
Question (MCQ)
Darwin's Finches are an excellent example of:
- (a) brood parasitism
- (b) connecting links
- (c) adaptive radiation
- (d) seasonal migration
Answer
Answer: (c) adaptive radiation
Darwin's finches demonstrate adaptive radiation as they evolved from a common ancestor into different species with specialized beaks adapted for different food sources.
17
Question (MCQ)
Palaeontological evidences for evolution refer to the:
- (a) development of embryo
- (b) homologous organs
- (c) fossils
- (d) analogous organs
Answer
Answer: (c) fossils
Palaeontological evidence refers to the study of fossils, which provide direct evidence of past life forms and their evolutionary relationships.
18
Question (MCQ)
Which one of the following scientist's name is correctly matched with the theory put forth by him?
- (a) de Vries - Natural selection
- (b) Mendel - Theory of Pangenesis
- (c) Weismann - Theory of continuity of germplasm
- (d) Pasteur - Inheritance of acquired characters
Answer
Answer: (c) Weismann - Theory of continuity of germplasm
Weismann proposed the theory of continuity of germplasm, which states that hereditary information is contained only in germ cells and cannot be influenced by changes in somatic cells.
19
Question (MCQ)
Which of the following organs are homologous?
- (a) Forelimbs of man and wings of bat
- (b) Wings of bat and bird
- (c) Wings of bat and pterodactyl
- (d) None of these
Answer
Answer: (a) Forelimbs of man and wings of bat
These organs have similar basic structure and origin (same developmental pattern) but different functions, making them homologous organs showing divergent evolution.
20
Question (MCQ)
Homologous organs show:
- (a) natural selection
- (b) divergent evolution
- (c) parallel evolution
- (d) convergent evolution
Answer
Answer: (b) divergent evolution
Homologous organs result from divergent evolution where organisms with common ancestry develop different functions for similar structures due to adaptation to different environments.
21
Question (MCQ)
Analogous organs arise due to:
- (a) divergent evolution
- (b) artificial selection
- (c) genetic drift
- (d) convergent evolution
Answer
Answer: (d) convergent evolution
Analogous organs arise due to convergent evolution where unrelated organisms develop similar structures with similar functions in response to similar environmental pressures.
22
Question (MCQ)
Evolution of life shows that life forms had a trend of moving from:
- (a) land to water
- (b) dryland to wet land
- (c) fresh water to sea water
- (d) water to land
Answer
Answer: (d) water to land
The evolution of life shows a general trend of organisms moving from aquatic environments to terrestrial environments, with major transitions occurring as organisms adapted to life on land.
23
Question (MCQ)
The bones of forelimbs of whale, bat, cheetah and man are similar in structure, because:
- (a) one organism has given rise to another
- (b) they share a common ancestor
- (c) they perform the same function
- (d) they have biochemical similarities
Answer
Answer: (b) they share a common ancestor
The structural similarity in forelimb bones of these different mammals indicates they evolved from a common ancestor and represent homologous structures showing divergent evolution.
24
Question (Assertion-Reason)
Assertion: Disruptive selection changes the population into two or more groups.
Reason: This type of selection favours average sized individuals.
Answer
Answer: Assertion is correct but the reason is wrong.
The assertion is correct as disruptive selection does change populations into distinct groups, but the reason is incorrect because disruptive selection favors extreme forms, not average-sized individuals.
25
Question (Assertion-Reason)
Assertion: Genetic drift refers to changes in allele frequency.
Reason: Heritable variations enable survival of the fittest.
Answer
Answer: Both statements are correct but the reason is not the correct explanation for the assertion.
Both statements are individually correct, but genetic drift is a random process unrelated to natural selection, so the reason doesn't explain the assertion.
26
Question (Assertion-Reason)
Assertion: Founder effect may lead to formation of new species.
Reason: Founders carry all the parental gene pool to a new location.
Answer
Answer: Assertion is correct but the reason is wrong.
The founder effect can indeed lead to new species formation, but founders carry only a limited portion of the parental gene pool, not all of it.
27
Question (Assertion-Reason)
Assertion: Louis Pasteur's experiments showed that new organisms appeared in an open flask with heat-killed yeast.
Reason: Life arises from pre-existing life.
Answer
Answer: Both statements are correct but the reason is not the correct explanation for the assertion.
The assertion is factually correct about Pasteur's experimental observations, and the reason states his conclusion, but they are not directly explanatory of each other.
28
Question (Assertion-Reason)
Assertion: Among the primates, chimpanzee is the closest relative of the present day humans.
Reason: DNA matching shows that human similarity is 100% with chimpanzee.
Answer
Answer: Assertion is correct but the reason is wrong.
Chimpanzees are indeed our closest living relatives, but DNA similarity is approximately 98-99%, not 100%.
29
Question (Assertion-Reason)
Assertion: The earliest cells used RNA as their hereditary molecule.
Reason: DNA evolved from RNA.
Answer
Answer: Both statements are correct but the reason is not the correct explanation for the assertion.
Both statements are scientifically accurate according to the RNA World hypothesis, but the reason doesn't directly explain why earliest cells used RNA.
30
Question (Assertion-Reason)
Assertion: Hardy Weinberg principle explains the occurrence of variations in population and species.
Reason: It concludes that disturbances in genetic equilibrium results in evolution.
Answer
Answer: Assertion is wrong but the reason is correct.
Hardy-Weinberg principle describes genetic equilibrium, not variations. However, disturbances in this equilibrium do indeed result in evolution.
31
Question (Assertion-Reason)
Assertion: Excessive use of herbicides and pesticides has no effect on resistant varieties of microbes.
Reason: Pathogenic bacteria are appearing in very short period of time because of chemical resistance.
Answer
Answer: Assertion is wrong but the reason is correct.
The assertion is incorrect because excessive use of chemicals does affect microbes by selecting for resistant varieties. The reason is correct as resistant pathogenic bacteria do emerge quickly.
32
Question (Assertion-Reason)
Assertion: Wings of butterfly and birds show analogy.
Reason: Analogous organs are anatomically different but functionally similar.
Answer
Answer: Both the assertion and reason are correct and the reason explains the assertion.
Wings of butterflies and birds are indeed analogous structures - they have different anatomical origins but serve the same function of flight.
33
Question (Assertion-Reason)
Assertion: Darwin's finches have different types of modified beaks according to their feeding habits.
Reason: Adaptive radiation leads to development of structures with different function arising from a common ancestor.
Answer
Answer: Both the assertion and reason are correct and the reason is the correct explanation for the assertion.
Darwin's finches demonstrate adaptive radiation perfectly, where different beak types evolved from a common ancestor to serve different feeding functions.
34
Question (Case-based)
A student was simulating Urey and Miller's experiment to prove the origin of life. The set-up used by the student is given. Find out the reasons why he could not get desired results.
Answer
The student could not get desired results because:
(a) O₂ was used instead of H₂ - The original experiment required a reducing atmosphere without oxygen
(b) Temperature maintained was 80°C instead of 800°C - The high temperature is crucial for simulating early Earth conditions and driving chemical reactions
35
Question (Case-based)
What conclusion was drawn by Urey and Miller through this experiment?
Answer
Urey and Miller concluded that life could have originated from pre-existing non-living organic molecules through chemical evolution. Their experiment demonstrated that organic compounds, including amino acids, could be synthesized from inorganic precursors under conditions simulating early Earth's atmosphere, supporting the hypothesis of abiogenesis.
36
Question (Case-based)
Compare the conclusion drawn with the theory of spontaneous generation.
Answer
Urey and Miller's experiment proved that life originated abiogenetically (from non-living matter through chemical processes), whereas the theory of spontaneous generation emphasized that units of life called spores were transferred to different planets including Earth. The key difference is that Urey-Miller demonstrated local chemical evolution versus spontaneous generation's concept of life transfer from elsewhere.
37
Question (Case-based)
Darwin found the varieties of finches when he travelled to Galapagos Islands and observed variations in them. What role does an individual organism play as per Darwin's theory of natural selection?
Answer
According to Darwin's theory of natural selection, an individual organism plays a crucial role by passing on its variations, mutations, and adaptations from one generation to another. Individuals with favorable traits survive and reproduce more successfully, transmitting these advantageous characteristics to their offspring, thus driving evolutionary change in populations over time.
38
Question (Case-based)
How did Darwin explain the existence of different varieties of finches on Galapagos Islands?
Answer
Darwin explained the existence of different varieties of finches through the process of adaptive radiation - the evolution of different species in a given geographical area starting from a common ancestor and literally radiating to other areas of geography (habitats). This process led to the development of different functional structures (particularly beak shapes) from a common ancestral form, with each variety adapted to specific food sources and ecological niches.
39
Question (Case-based)
What is fitness of an individual according to Darwin?
Answer
According to Darwin, fitness of an individual is the ability of an organism to survive and pass on its genes to future generations. It is not just about physical strength or survival, but specifically about reproductive success - the capacity to survive to reproductive age and successfully produce viable offspring that can themselves reproduce. This concept is central to natural selection.
40
Question (Case-based)
Study the diagram given below and answer the following questions: Mention the specific geographical region where these organisms are found.
Answer
Australia
The organisms shown in the diagram are found in Australia, which is known for its unique marsupial fauna that evolved in isolation after the continent separated from other landmasses.
41
Question (Case-based)
Name and explain the phenomenon that has resulted in the evolution of such diverse species in the region.
Answer
The phenomenon is adaptive radiation (also called divergent evolution). This is the process of evolution of different species in a given geographical area starting from a common ancestor and radiating to other areas of geography and habitats. It involves the development of different functional structures from a common ancestral form. In Australia, marsupials underwent adaptive radiation after geographical isolation, evolving into diverse species adapted to different ecological niches - from tree-dwelling koalas to ground-dwelling kangaroos to carnivorous Tasmanian devils.
Key Points to Remember
- Natural selection explains antibiotic resistance in bacteria through survival of the fittest
- Adaptive radiation is exemplified by Darwin's finches with diverse beak adaptations
- Human evolution shows progressive development, not adaptive radiation
- Homologous organs show divergent evolution, analogous organs show convergent evolution
- Urey-Miller experiment demonstrated abiogenesis from non-living matter
- Stabilizing selection favors intermediate traits, disruptive selection favors extremes
- Fitness in Darwinian terms means reproductive success, not physical strength
Additional Information
Understanding evolution is crucial for comprehending life's diversity and the mechanisms that drive biological change. The concepts covered in these 41 questions form the foundation of evolutionary biology.
Important Evolutionary Concepts
- Natural Selection and its types (stabilizing, directional, disruptive)
- Adaptive radiation and speciation
- Evidence for evolution (fossils, embryology, biogeography, molecular)
- Human evolution and its stages
- Origin of life theories and experimental evidence
These questions are essential for:
- CBSE Class 12 Biology examinations
- Competitive entrance exams (NEET, JEE)
- Building conceptual understanding of evolutionary processes
- Preparing for higher studies in biological sciences
NCERT Solutions Class 12 Biology Chapter 7 Evolution
Questions 42-59 - Complete Solutions with Detailed Explanations
42
Question
(a) Name the primates that lived about 15 million years ago. List their characteristic features.
(b) (i) Where was the first man-like animal found?
(ii) Write the order in which Neanderthals, Homo habilis and Homo erectus appeared on earth. State the brain capacity of each one of them.
(iii) When did modern Homo sapiens appear on this planet?
Answer
(a) The primates that lived about 15 million years ago were Dryopithecus and Ramapithecus.
Their characteristic features:
- They were hairy and walked like gorillas and chimpanzees
- Ramapithecus was more man-like
- Dryopithecus was more ape-like
(b)(i) The first man-like animal was found in Ethiopia and Tanzania.
(ii) The order of appearance from earliest to latest: Homo habilis → Homo erectus → Neanderthals
- Homo habilis: 650-800 cc brain capacity
- Homo erectus: 900 cc brain capacity
- Neanderthals: 1400 cc brain capacity
(iii) Modern Homo sapiens appeared between 75,000-10,000 years ago.
43
Question
Life originated from earth's inorganic atmosphere in past but not today. Suggest two reasons.
Answer
Life cannot originate from earth's inorganic atmosphere today because:
- Presence of free oxygen in present day atmosphere - oxygen prevents the formation of complex organic molecules from simple inorganic compounds
- Very high temperatures - the extreme conditions needed for abiotic synthesis are not naturally present on Earth today
44
Question
How can you suggest that biochemistry gives evidence for organic evolution?
Answer
Biochemistry provides evidence for organic evolution because similar types of proteins are found in organisms of the same species or group. This biochemical similarity indicates common ancestry and supports the theory that related organisms evolved from common predecessors, sharing similar metabolic pathways and molecular structures.
45
Question
State the significance of the study of fossils in evolution.
Answer
The significance of studying fossils in evolution includes:
- Represent extinct organisms - fossils provide direct evidence of organisms that lived in the past
- Show life forms restricted to certain geological time spans - help establish timeline of evolutionary events
- Show ancestry of present day organisms - demonstrate evolutionary relationships
- Act as connecting links between two groups of organisms, showing transitional forms
46
Question
What is fossil?
Answer
Fossils are the remains or impressions of ancient organisms preserved in sedimentary rocks or other media. They provide physical evidence of life forms that existed in the past and are crucial for understanding evolutionary history.
47
Question
How do we compute the age of a fossil?
Answer
The age of a fossil is computed by radiocarbon dating. This method measures the decay of radioactive isotopes (like Carbon-14) in the fossil remains to determine how long ago the organism died.
48
Question
Identify the examples of convergent evolution from the following:
- (i) Flippers of penguins and dolphins
- (ii) Eyes of octopus and mammals
- (iii) Vertebrate brains
Answer
Examples of convergent evolution are:
- (i) Flippers of penguins and dolphins - similar structure evolved independently for swimming
- (ii) Eyes of octopus and mammals - similar complex eyes evolved independently for vision
Note: Vertebrate brains represent divergent evolution, not convergent evolution.
49
Question
If abiotic origin of life is in progress on a planet other than earth, what should be the condition there? Explain.
Answer
For abiotic origin of life to occur on another planet, the following conditions should be present:
- Reducing atmosphere - no free oxygen should be present, as oxygen prevents formation of organic molecules
- Continuous supply of energy - from sources like lightning, thunder, volcanic eruptions, or stellar radiation
- Presence of autocatalyst or self-replicating molecules - essential for the formation and propagation of life
50
Question
What must have provided energy for the warmth for life to originate on primitive earth? Name the first organism to release oxygen into the atmosphere.
Answer
Energy for life to originate on primitive earth was provided by:
- Heat from the earth's core and volcanic activity
- Cosmic rays from outer space
- Lightning in the primitive atmosphere
Cyanobacteria was the first organism to release oxygen into the atmosphere through photosynthesis.
51
Question
Write the Oparin and Haldane's hypothesis about the origin of life on Earth. How does meteorite analysis favour this hypothesis?
Answer
Oparin and Haldane's Hypothesis:
The hypothesis stated that life originated from pre-existing non-living organic molecules (such as RNA, proteins, etc.) under the primitive earth conditions.
Support from Meteorite Analysis:
When meteorites were analyzed, similar compounds were found in them, which confirms that similar chemical processes that led to life on Earth are also occurring elsewhere in space, supporting the hypothesis of chemical evolution.
52
Question
Mention the contribution of S.L. Miller's experiments on Origin of Life.
Answer
S.L. Miller's contributions to understanding the origin of life:
Miller created an environment in laboratory similar to primitive earth conditions. In a closed flask containing:
- CH₄ (methane)
- H₂ (hydrogen)
- NH₃ (ammonia)
- Water vapour
At 800°C with electric discharge (simulating lightning), after a week they observed:
- Formation of amino acids
- Complex molecules like sugars, nitrogen bases, pigments and fats
This provided experimental evidence for the theory of chemical origin of life.
53
Question
Convergent evolution and divergent evolution are the two concepts explaining organic evolution. Explain each one with the help of an example. OR Differentiate between divergent and convergent evolution. Give one example of each.
Answer
| Convergent Evolution | Divergent Evolution |
|---|---|
| Definition: When more than one adaptive radiation appeared to have occurred in an isolated geographical area and two or more groups of unrelated animals resemble each other for similar mode of life or habitat | Definition: When the same structures developed along different directions due to adaptations to different needs |
| Example: Australian marsupials and placental mammals - unrelated groups that evolved similar characteristics | Example: Forelimbs of whales, bats, cheetah and humans - similar anatomical structure but different functions |
| Result: Different species develop similar structures | Result: Related species develop different structures |
54
Question
Explain convergent evolution with the help of two examples.
Answer
Convergent Evolution: Different structures evolved similarly due to same functions.
Examples:
- Wings of butterfly and birds - Both evolved wings for flight, but butterflies (insects) and birds (vertebrates) are completely unrelated groups. Their wings have different anatomical structures but serve the same function.
- Sweet potato and potato - Sweet potato is a root modification while potato is a stem modification, but both evolved as storage organs and appear similar in function despite different origins.
55
Question
Fitness is the end result of the ability to adapt and get selected by nature. Explain with suitable example.
Answer
Fitness is based on inherited characteristics and the ability to adapt to changing environments. It results in survival of fit individuals while unfit ones are eliminated.
Example - Industrial Melanism in England:
Before Industrialization:
- White-winged moths were more numerous than dark-winged moths
- Tree trunks were covered by white lichens
- Dark-colored moths were easily spotted and eaten by predators on white backgrounds
After Industrialization:
- Dark-winged moths became more numerous
- Tree trunks became dark due to dust and coal particles
- White moths were easily spotted and eaten on dark backgrounds
This demonstrates that fitness depends on environmental conditions and shows how industrial melanism supports evolution by natural selection.
56
Question
(a) How does Hardy-Weinberg equation explain genetic equilibrium?
(b) Describe how does this equilibrium get disturbed which may lead to founder effect.
Answer
(a) Hardy-Weinberg Equation and Genetic Equilibrium:
The Hardy-Weinberg equation is: p² + 2pq + q² = 1
This means:
- The sum total of all allelic frequencies is 1
- p² = probability of allele AA appearing on both chromosomes
- q² = probability of allele aa appearing on both chromosomes
- 2pq = probability of Aa genotype
(b) Disturbance Leading to Founder Effect:
The equilibrium gets disturbed due to genetic drift - changes in allele frequencies occurring by chance.
When genetic drift causes such significant changes in allele frequency that the population becomes a different species, the original population becomes founders and this effect is called the founder effect.
57
Question
Evolution is a change in gene frequencies in a population in response to changes in the environment in a time scale of years and not centuries. Justify this statement with reference to DDT. How does the theory of Hugo de Vries support this?
Answer
DDT Resistance Example:
When DDT was first used:
- Maximum mosquitoes died, but few survived due to natural variation in the population
- These surviving mosquitoes showed resistance to DDT
- They reproduced successfully in the presence of DDT
- Gradually, the entire mosquito population became DDT resistant within a few years
Hugo de Vries' Theory Support:
According to Hugo de Vries, evolution is caused by sudden large differences (mutations) in the population and not minor variations. The rapid development of DDT resistance demonstrates that significant evolutionary changes can occur quickly through major mutations rather than gradual minor changes over centuries.
58
Question
Describe the three different ways by which Natural Selection can affect the frequency of a heritable trait in a population.
Answer
Factors Affecting Gene Frequencies:
- Gene Migration/Gene Flow: When individuals migrate to another population, new genes are added to the new population and lost from the old population, changing frequencies.
- Genetic Drift: Changes in frequencies occurring by chance. Sometimes leads to founder effect when drifted population forms different species.
- Mutation: Advantageous mutations lead to new phenotypes and result in speciation over generations.
- Genetic Recombination: During gametogenesis, variations due to recombination create new phenotypes.
- Natural Selection: Heritable variations enabling survival of the fittest leave greater progeny.
Three Effects of Natural Selection:
- Stabilization: Larger number of individuals acquire mean character value, making the peak higher and narrower
- Directional Change: Large number of individuals acquire values other than mean, shifting the peak in one direction
- Disruption: Large number of individuals acquire peripheral character values at both ends, forming 2 peaks
59
Question
(a) Name the primates that lived about 15 million years ago. List their characteristic features.
(b) (i) Where was the first man-like animal found?
(ii) Write the order in which Neanderthals, Homo habilis and Homo erectus appeared on earth. State the brain capacity of each one of them.
(iii) When did modern Homo sapiens appear on this planet?
Answer
(a) The primates that lived about 15 million years ago were Dryopithecus and Ramapithecus.
Their characteristic features:
- They were hairy and walked like gorillas and chimpanzees
- Ramapithecus was more man-like
- Dryopithecus was more ape-like
(b)(i) The first man-like animal was found in Ethiopia and Tanzania.
(ii) The order of appearance from earliest to latest: Homo habilis → Homo erectus → Neanderthals
- Homo habilis: 650-800 cc brain capacity
- Homo erectus: 900 cc brain capacity
- Neanderthals: 1400 cc brain capacity
(iii) Modern Homo sapiens appeared between 75,000-10,000 years ago.
Key Points to Remember
- Human evolution shows progressive increase in brain capacity from Homo habilis (650-800 cc) to Neanderthals (1400 cc)
- Fossils provide direct evidence of evolution through preserved remains of ancient organisms
- Miller's experiment proved that organic molecules can form from inorganic compounds under primitive earth conditions
- Convergent evolution produces similar structures in unrelated organisms due to similar environmental pressures
- Hardy-Weinberg principle explains genetic equilibrium in populations under ideal conditions
- Natural selection can cause stabilizing, directional, or disruptive changes in populations
Additional Information
Understanding evolution involves multiple interconnected concepts:
Evolution Timeline
- Chemical evolution preceded biological evolution
- First life forms appeared approximately 3.8 billion years ago
- Human evolution represents only the most recent phase of evolutionary history
Key evolutionary mechanisms include:
- Natural selection acting on genetic variation
- Genetic drift causing random changes in small populations
- Gene flow introducing new alleles through migration
- Mutation providing raw material for evolutionary change