Evolution - Class 12 Biology - Chapter 6 - Notes, NCERT Solutions & Extra Questions
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Extra Questions - Evolution | NCERT | Biology | Class 12
According to neo-Darwinism, evolution is due to:
A. Gene flow
B. Change in gene structure
C. Change in size of gene pool
D. Change in gene frequency
The correct answer is D. Change in gene frequency.
Neo-Darwinism theory statements that evolution occurs through changes in gene frequencies within populations over time. This alteration in the frequency of alleles underlies the evolutionary process.
Select the incorrect statements: (A) The essence of Darwinian theory of evolution is natural selection. (B) Evolution is a directed process in the sense of determinism. (C) The geological history of Earth is not related to the biological history of Earth. (D) During evolution, the rate of appearance of new forms is linked to the life cycle.
A. A and B
B. B and C
C. A and D
D. B and D
The correct option is B (B and C).
Statement (B) claims that evolution is a directed process in the sense of determinism. This is incorrect because evolution is largely influenced by random events such as environmental changes and genetic mutations, making it an undirected process.
Statement (C) suggests that the geological history of Earth is not related to the biological history of Earth, which is also incorrect. The geological and biological histories are interconnected; changes in the Earth's geology often impact the development and evolution of life on the planet.
A gradual change, over a long period, in a form of life is known as: (a) erosion (b) evolution (c) revolution (d) evaluation
The correct answer is (b) evolution.
Evolution is defined as the sequence of gradual changes that occur in primitive organisms over millions of years, leading to the formation of new species. This process explains how different forms of life have developed and diversified from earlier forms throughout the history of the earth.
What kind of evidence suggests that man is more closely related to the chimpanzee than to other hominoid apes?
A Comparison of chromosome morphology only
B Evidence from fossil remains and fossil mitochondrial DNA alone
C Evidence from DNA extracted from sex chromosomes, autosomes, and mitochondria
D Evidence from DNA from sex chromosomes only
The correct answer is C - Evidence from DNA extracted from sex chromosomes, autosomes, and mitochondria.
Evidence from DNA from various parts of the genome, including sex chromosomes, autosomes, and mitochondria, strongly suggests that humans are more closely related to chimpanzees than to other hominoid apes. Humans and chimpanzees share a common ancestor and have approximately 99% genetic similarity. This comprehensive DNA comparison encompasses more than just one part of the genome, providing a broader and more accurate indication of evolutionary relationships.
According to Darwin, evolution is:
A. A sudden but discontinuous process
B. A slow and discontinuous process
C. A slow and continuous process
D. A slow, sudden, and discontinuous process
Correct Answer: C
Explanation: According to Darwin's theory of evolution, the process of evolution is a slow and continuous development. Over long periods, this gradual change supports the formulation and evolution of new species, distinguishing different traits and adaptations. This continuous nature of evolution contrasts with theories that suggest abrupt or sporadic changes. Thus, the answer is C. A slow and continuous process.
The expression "survival of the fittest" means that -
A. The powerful shall live and the weak shall die.
B. The powerful, as well as the weak, shall live peacefully.
C. The powerful shall help the weak in the process of survival.
D. Both the powerful and the weak shall live.
The correct answer is A. The powerful shall live and the weak shall die.
Answer: 65) (A) The expression "survival of the fittest" signifies that the powerful shall live and the weak shall die, emphasizing the concept where only the strongest and most capable individuals or species survive, while others may not.
Directions for questions 1 to 5: The following table gives the marks scored by 5 students in 4 different subjects (out of 100) during a monthly test. Study the data carefully and answer the questions that follow:
Year | Physics | Chemistry | Biology | Mathematics |
---|---|---|---|---|
Abin | 50 | 85 | 59 | 78 |
Bobby | 85 | 100 | 67 | 88 |
Chris | 60 | 70 | 80 | 90 |
Davis | 95 | 99 | 100 | 100 |
What was Bobby's score in Biology?
A. 67
B. 59
C. 98
D. 80
The correct answer is Option A: 67.
From the table provided, we can see that Bobby's score in Biology is 67.
State whether true or false: Mutation theory fails to explain the significant impact of mutation on evolution.
A) True
B) False
Answer: A) True
Explanation: The Mutation Theory was first proposed by Hugo de Vries, who argued that mutations are the sole drivers of speciation and evolution. However, one critical point against this theory is the relatively low frequency of mutations; they occur in only about one out of several million genes. Given this low rate, it is challenging to justify how mutations alone can exert a significant impact on the evolutionary process. Therefore, the statement that mutation theory fails to explain the significant impact of mutation on evolution is true.
Phylogeny is the study of: A. Development of an individual. B. Evolution of species. C. Embryonic development of an organ. D. Ecological adaptation of an organism.
Phylogeny refers to the study of the evolution of species. It involves understanding how different organisms are related through evolutionary history and exploring the diversity of life over time. Using phylogenetic methods, we can trace the lineage of organisms and see how they have evolved from a common ancestor.
The correct answer to the question "Phylogeny is the study of" is:
B. Evolution of species.
This option best reflects what phylogeny focuses on—it is not about the development of an individual (embryonic or otherwise), nor is it concerned with the ecological adaptation of a single organism. Rather, phylogeny is all about the broader picture of how different life forms have changed over generations to result in the biodiversity we observe today.
Match the items given in Column A and Column B, and identify the correct alternative listed below.
Column A | Column B |
---|---|
(a) Flying fish | (i) Draco |
(b) Flying lizard | (ii) Echidna |
(c) Egg laying mammal | (iii) Exocoetus |
(d) Flightless bird |
A. (a)-(i), (b)-(iii), (c)-(ii), (d)-(iv)
B. (a)-(iii), (b)-(i), (c)-(ii), (d)-(iv)
C. (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)
D. (a)-(i), (b)-(iii), (c)-(iv), (d)-(ii)
Here's a refined explanation of the match between Column A and Column B based on the descriptions provided:
Flying Fish: According to the transcript, Exocetus refers to the flying fish type of marine bony fish that utilizes its fins to glide similarly to how the flying lizard glides with its wing-like structures. Therefore:
(a) Flying Fish matches with (iii) Exocoetus.
Flying Lizard: The text mentions the Draco as being identified with a flying lizard because it has membranes that enable it to glide. Hence:
(b) Flying Lizard matches with (i) Draco.
Egg-laying Mammal: The Echidna is mentioned as a warm-blooded mammal, comparable to birds in some reproductive aspects because it lays eggs. So:
(c) Egg laying mammal matches with (ii) Echidna.
Flightless Bird: The transcript identifies the ostrich, called Struthio scientifically, as a large, flightless bird due to its wings being unable to support flight despite their presence. Thus:
(d) Flightless bird matches with (iv) Struthio.
Based on this analysis, the correct matching from the options provided would be:
B
(a)-(iii), (b)-(i), (c)-(ii), (d)-(iv)
The scientist who proposed the theory of natural selection was -
A. Lamarck
B. Charles Darwin
C. Waldayer
D. Muller
The question asks which scientist proposed the theory of natural selection.
Natural selection is a theory where it is stated that the organisms which adapt most effectively to their habitat are the ones that will survive and reproduce over the long term. This process leads to the propagation and emergence of new strains adapted to the environment.
Jean-Baptiste Lamarck, another scientist mentioned, had ideas about organisms evolving over generations through the use of or disuse of parts, but this is different from natural selection. He suggested that structures that are used extensively would develop further, while those that are not used would eventually disappear in future generations.
However, Charles Darwin was the scientist who formally proposed the theory of natural selection in 1859. This theory fundamentally explains how living organisms evolve and adapt to their environmental resources based mostly on natural selection.
The other names mentioned:
Waldayer is known for identifying chromosomes in 1888.
Muller identified genetic mutations in 1927.
Therefore, the correct answer is:
B. Charles Darwin
Human evolution was supposed to take place in:
A) America
B) Asia
C) Africa
D) Australia
The correct answer to the question of where human evolution took place is C) Africa. Based on archaeological and fossil evidence, the earliest human-like features have been traced back primarily to Africa. Studies and findings have shown that the origin of the first human ancestors, known as "hominins," originated in Africa more than two to six million years ago.
Over time, these early ancestors developed various skills and features pivotal to human evolution. After originating in Africa, they migrated to other parts of the world, including Asia and European countries. Therefore, the historical record and evolutionary evidence strongly support that the cradle of human evolution is in Africa, marking it as the point of origin for our ancestors. Thus, the correct choice is: C) Africa.
Which one of the following statements is true with respect to photosynthesis?
A. Oxygen evolved during photosynthesis comes from $\mathrm{CO}_{2}$.
B. Chlorophyll is the only photosynthetic pigment in plants.
C. Photosynthesis occurs in the stem of some plants.
D. Photosynthesis does not occur in red light.
The true statement about photosynthesis from the given options is:
C. Photosynthesis occurs in the stem of some plants.
Here’s why the other statements are incorrect and an elaboration on why statement C is correct:
A. Oxygen evolved during photosynthesis comes from $\mathrm{CO}_{2}$.
This statement is false. Oxygen released during photosynthesis is derived from the splitting of water (H$_2$O) molecules through photolysis, not from carbon dioxide (CO$_2$).B. Chlorophyll is the only photosynthetic pigment in plants.
This statement is incorrect. Alongside chlorophyll, plants contain other photosynthetic pigments such as carotenoids and phycobilins, which play roles in capturing light energy.C. Photosynthesis occurs in the stem of some plants.
This statement is true. In certain plants, especially some herbs and young or non-woody shrubs, the stems can contain chlorophyll and are capable of photosynthesis, mainly because these parts need to maximize light capture when understory plants overshadow them.D. Photosynthesis does not occur in red light.
This statement is false. Chlorophyll, the primary pigment in photosynthesis, efficiently absorbs red light (around 600–700 nm), making it one of the most effective wavelengths for photosynthesis.
Therefore, the true statement regarding photosynthesis among the provided options is that photosynthesis can occur in the stems of some plants.
Which of the following traits would an evolutionary biologist consider to understand the divergent evolution process?
A Hind limb of sheep, flipper of whale, and wing of a bat.
B Flipper of a shark, flipper of a penguin, and flipper of a dolphin.
C Bat wing, bird wing, and wing of a butterfly.
D Human arm, seal forelimb, and wing of a bird.
To understand divergent evolution, it's essential to recognize how from a common ancestor species diversify and develop into distinct forms. Divergent evolution illustrates the process where species evolve different traits due to adaptations to various environmental factors, leading them to serve diverse functional roles despite having shared ancestry.
Here is an analysis of each given option to find the best example that highlights divergent evolution:
Option A: Hind limb of sheep, flipper of whale, and wing of a bat.
This option isn't entirely fitting because it includes limbs that serve different functions and might not originate from a common ancestor specifically adapted for these varied functions.
Option B: Flipper of a shark, flipper of a penguin, and flipper of a dolphin.
This example is more aligned with convergent evolution where different species have evolved to have similar structures due to similar environmental pressures rather than from a common ancestor specialized in that body part.
Option C: Bat wing, bird wing, and wing of a butterfly.
In this case, although "wings" serve the same function of flying, the structures originate from entirely different ancestral backgrounds. This contrasts more with divergent evolution and is again an instance of convergent evolution.
Option D: Human arm, seal forelimb, and wing of a bird.
This option is a textbook example of divergent evolution. All these limbs originate from a common tetrapod ancestor. Despite their diverse current functions—grasping, swimming, and flying—they evolved from the same ancestral structure.
Therefore, the correct answer that represents divergent evolution the best is Option D. Here, we see a single type of ancestral limb diversifying into structures adapted to perform different functions in their respective species.
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Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.
Antibiotic resistance in bacteria is a clear example of natural selection in action, as proposed by Charles Darwin. Here's how it works:
Variation: Within a bacterial population, there is natural genetic variation. Some bacteria may have random mutations that make them slightly more resistant to a particular antibiotic.
Selection Pressure: When an antibiotic is introduced, it creates a selection pressure. Most bacteria are killed by the antibiotic, but those with resistance mutations survive.
Survival of the Fittest: The resistant bacteria are "fitter" in this new environment (i.e., the presence of the antibiotic). They survive while the non-resistant bacteria perish.
Reproduction: The resistant bacteria reproduce and pass their resistant genes to the next generation. Over time, the population of bacteria will have a higher proportion of resistant individuals.
Spread of Resistance: The more an antibiotic is used, the more it selects for resistant bacteria. Eventually, these bacteria may spread and become the dominant strain.
Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.
Recent fossil discoveries and controversies about evolution have been reported in various newspapers and popular science articles. Some notable examples include:
1. Confuciusornis: Two unusual fossils of primitive birds, including the genus Confuciusornis, have been discovered in China, sparking controversy over the evolution of birds.
2. Antarctanax: The discovery of Antarctanax shackletoni, an early dinosaur relative, in Antarctica has provided insights into the rapid evolution of archosaurs following a mass extinction event.
3. Eretmorhipis: A marine reptile with a platypus-like bill and bony plates along its back, Eretmorhipis carrolldongi, has been found in China, highlighting convergent evolution between this ancient species and modern platypuses.
4. Galagadon: The discovery of a small shark with spaceship-shaped teeth, Galagadon nordquistae, in South Dakota has shed light on the marine environment in which dinosaurs like SUE the T. rex lived.
5. Early Vertebrates: Research on early vertebrates has revealed their remarkable transformations during their evolutionary history, leading to the diverse and adaptable beings we know today.
6. Early Plants: The evolution of early plants has been studied, showing how they underwent significant transformations, leading to the complex ecosystems we see today.
7. Early Invertebrates: The evolution of early invertebrates has also been explored, highlighting their remarkable transformations and the diverse and complex beings they evolved into.
These discoveries and research have contributed significantly to our understanding of evolution and the history of life on Earth.
Attempt giving a clear definition of the term species.
A species can be defined as a group of organisms that share common characteristics and are *capable of interbreeding* to produce fertile offspring. This classification is often used in the context of reproductive isolation from other groups, meaning that members of one species do not normally interbreed with members of another species in natural conditions. This concept helps in understanding the biodiversity and evolution of life forms.
Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.) 120 words
Human evolution showcases various adaptations:
-
Brain Size and Function: Early hominids like Australopithecus had smaller brains (~400-500 cc). Over time, species like Homo habilis (~650-800 cc) and Homo erectus (~900 cc) showed an increase in brain size. Modern humans, Homo sapiens, have brains around 1400 cc, enabling advanced cognitive functions, tool use, and language.
-
Skeletal Structure: Early humans had robust skeletons adapted for climbing. Bipedalism evolved, evidenced by skeletal adaptations in the pelvis and leg bones, allowing upright walking.
-
Dietary Preference: Early hominids were mostly herbivorous. Homo habilis used tools for hunting, introducing meat into their diet. Homo erectus likely consumed more meat, aiding brain development.
-
Social Behavior: Evolution of social structures, use of fire, and development of language played vital roles in survival and cultural advancements.
Find out through internet and popular science articles whether animals other than man has self-consciousness.
Recent research and discoveries have shed light on the self-consciousness of animals other than humans. Several species have been found to possess self-awareness, including:
1. Dolphins: Known to exhibit self-awareness and even commit suicide in captivity, dolphins have been observed to recognize themselves in mirrors and display complex social behaviors.
2. Orangutans: These great apes have been observed to use tools and display signs of self-awareness, such as recognizing themselves in mirrors.
3. Chimpanzees: Similar to orangutans, chimpanzees have been found to exhibit self-awareness through mirror tests and complex social behaviors.
4. Gorillas: Some gorilla species have been observed to display signs of self-awareness, such as recognizing themselves in mirrors.
5. Elephants: These highly social animals have been found to exhibit self-awareness and display complex behaviors such as mourning and cooperation.
6. Bonobos: Similar to chimpanzees, bonobos have been observed to exhibit self-awareness through mirror tests and complex social behaviors.
7. Bottlenose Dolphins: These dolphins have been found to exhibit self-awareness at an earlier age than humans and chimpanzees.
8. Asian Elephants: These elephants have been observed to display signs of self-awareness, such as recognizing themselves in mirrors.
9. Octopuses: While not necessarily self-aware in the same way as other animals, octopuses have been found to exhibit complex behaviors and problem-solving abilities that suggest a level of consciousness.
These discoveries highlight the complexity and diversity of animal consciousness, with many species exhibiting signs of self-awareness and complex behaviors.
List 10 modern-day animals and using the internet resources link it to a corresponding ancient fossil. Name both.
Crocodiles
*Modern Animal*: Crocodylus porosus
*Fossil*: DeinosuchusBirds
*Modern Animal*: Columba livia (Rock Pigeon)
*Fossil*: ArchaeopteryxWhales
*Modern Animal*: Balaenoptera musculus (Blue Whale)
*Fossil*: BasilosaurusHorses
*Modern Animal*: Equus ferus caballus (Domestic Horse)
*Fossil*: EohippusElephants
*Modern Animal*: Loxodonta africana (African Elephant)
*Fossil*: Mammuthus primigenius (Woolly Mammoth)Giraffes
*Modern Animal*: Giraffa camelopardalis
*Fossil*: GiraffatitanWolves
*Modern Animal*: Canis lupus (Gray Wolf)
*Fossil*: Canis dirus (Dire Wolf)Camels
*Modern Animal*: Camelus dromedarius (Dromedary Camel)
*Fossil*: CamelopsSalamanders
*Modern Animal*: Salamandra salamandra (Fire Salamander)
*Fossil*: Beiyanerpeton jianpingensisPenguins
*Modern Animal*: Aptenodytes forsteri (Emperor Penguin)
*Fossil*: Waimanu
This list links each modern-day animal with an ancient fossil that represents its evolutionary lineage through time.
Describe one example of adaptive radiation.
An excellent example of adaptive radiation is Darwin's Finches found on the Galapagos Islands. During his journey to these islands, Charles Darwin observed a striking diversity in the shape and size of the finches' beaks.
Key Points:
Diversification: Starting from a common ancestor, these birds diversified into multiple species, each with its own unique beak shape and size adapted to different food sources.
Adaptation: Different beak forms allowed these finches to exploit different food resources such as seeds, insects, and fruits. For example:
Seed-eating finches developed strong, large beaks to crack seeds.
Insectivorous finches evolved slender, sharp beaks to catch insects.
Isolation: The geographical isolation of the Galapagos Islands played a significant role in this process, leading to different populations adapting to their specific environments.
Illustration:
Here is a diagram highlighting the different beak shapes of Darwin's Finches:
This phenomenon is called adaptive radiation because:
The evolution started from a common point (the ancestral species) and then radiated outwards to fill various ecological niches.
Conclusion:
Darwin's Finches serve as a classic example of adaptive radiation, demonstrating how different species can evolve from a common ancestor to exploit different ecological niches.
Can we call human evolution as adaptive radiation?
Adaptive radiation refers to the process by which organisms diversify rapidly into a multitude of new forms, particularly when a change in the environment makes new resources available, creates new challenges, or opens new environmental niches.
Human evolution, however, does not typically fit this definition. Humans evolved from a common ancestor with other primates through a gradual process involving natural selection and genetic variation. While there was significant diversification in various hominid species (like Australopithecus, Homo habilis, Homo erectus, etc.), this process doesn't fit the rapid and radiation aspect found in classical examples of adaptive radiation, such as Darwin's finches on the Galapagos Islands.
Instead, human evolution is a classic example of branching descent and natural selection rather than adaptive radiation. Humans adapted to various environments over long periods of time, but this diversification wasn't as rapid or extensive as seen in adaptive radiation events.
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.
Let's trace the evolutionary stages of the horse. The evolution of the horse is one of the most well-documented cases of evolutionary change and provides an excellent example of how species adapt over time through natural selection.
Evolutionary Stages of the Horse
1. Eohippus (Hyracotherium)
Time Period: ~55 million years ago (Eocene Epoch)
Description:
Size of a small dog (about 0.4 meters tall at the shoulders).
Had 4 toes on the front legs and 3 toes on the hind legs.
Lived in forests and was a browser, feeding on soft leaves and plant material.
2. Mesohippus
Time Period: ~37-32 million years ago (Late Eocene to Early Oligocene Epoch)
Description:
Larger than Eohippus (about 0.6 meters tall at the shoulders).
Had 3 toes on each foot, with the middle toe becoming more prominent.
Evolved to live in more open, but still wooded environments.
Teeth were more adapted to chewing tougher plant material.
3. Miohippus
Time Period: ~32-25 million years ago (Late Oligocene Epoch)
Description:
Slightly larger than Mesohippus.
Retained 3 toes but showed further elongation of the middle toe.
Continued adaptation towards more open environments.
4. Merychippus
Time Period: ~17-11 million years ago (Miocene Epoch)
Description:
About 1 meter tall at the shoulders.
Middle toe became more dominant, supporting most of the body weight.
First horse to develop teeth adapted to grazing on grasses, indicating a move to plains and grassland habitats.
**5. Pliohippus (Potential Ancestor to Modern Horses)
Time Period: ~5-10 million years ago (Late Miocene Epoch)
Description:
Similar in appearance to modern horses but smaller.
Had one large central toe (hoof) on each foot with vestigial side toes.
The structure of legs and teeth further optimized for running and grazing.
**6. Equus (Modern Horses)
Time Period: ~4 million years ago to present (Pliocene to Present)
Description:
Genus to which all modern horses belong.
Single-toed with a well-developed hoof.
Adapted to various environments around the globe, with specialized breeding leading to a variety of different horse breeds.
Height can vary significantly, but generally much larger than their early ancestors, capable of speeds and endurance necessary for survival in open plains.
Key Points in Horse Evolution
Adaptation to Environment: Early horses lived in dense forests and evolved to survive in open grasslands as these replaced woodlands due to climate changes.
Toes to Hooves: Reduction in the number of toes as adaptations moved from soft forest floors to harder, more open terrain.
Teeth Adaptation: Evolution from browsing teeth to grazing teeth to adapt to a diet of tough grasses.
Diagrammatic Representation (Figure)
References:
Evolutionary Biology Textbooks
Library Resources on Paleontology
Discussion with Biology Teachers
These evolutionary stages highlight natural selection and adaptation specific to the changing environments the horse lineage experienced. This transformation from a small forest-dwelling creature to the modern horse is a profound example of evolutionary processes.
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Comprehensive Evolution Class 12 Notes: A Detailed Guide for Students
Introduction
Evolutionary Biology is the study of the history of life forms on Earth. To comprehend the changes in flora and fauna that have occurred over millions of years, an understanding of the origin of life and the universe is essential. This article delves into the fascinating processes of evolution and the evidence supporting them.
Origin of Life
The Big Bang Theory
The Big Bang Theory explains the origin of the universe through a massive explosion that occurred around 20 billion years ago. This event led to the formation of galaxies, stars, and eventually, planets, including Earth.
Early Earth Conditions
Earth formed about 4.5 billion years ago. Initially, it lacked an atmosphere, and volcanic eruptions were rampant. Over time, water vapour condensed to form oceans, creating a suitable environment for life.
The First Appearance of Life
The origin of life on Earth is considered a unique event. Early theories such as panspermia
and spontaneous generation
have been explored but largely dismissed. Instead, the chemical evolution theory by Oparin and Haldane is widely accepted.
Theories of Origin
- Theory of Spontaneous Generation: Suggested life arises from non-living matter.
- Chemical Evolution Theory: Proposed by Oparin and Haldane, it indicates life formed from non-living organic molecules.
Miller's Experiment
In 1953, S.L. Miller simulated early Earth conditions and observed the formation of amino acids. This experiment provided strong evidence supporting the chemical evolution theory.
Evolution of Life Forms
Theory of Special Creation
Traditional belief that all species were created as they are and remain unchanged over time.
Darwin’s Theory of Natural Selection
Based on observations, Charles Darwin proposed that species evolve over time through natural selection. Traits that enhance survival and reproduction are passed on to future generations.
Alfred Wallace’s Contribution
Simultaneously with Darwin, Alfred Wallace arrived at similar conclusions about natural selection and evolution.
Evidences for Evolution
Fossils and Paleontological Evidence
Fossils, the preserved remains of organisms, provide a timeline of life on Earth, showing how species have evolved over millions of years.
Embryological Evidence
Common embryonic features among vertebrates suggest a shared ancestry.
Comparative Anatomy and Morphology
Similar structures in different species, such as forelimbs in mammals, indicate divergent evolution from a common ancestor.
graph LR
A[Common Ancestor] --> B[Whales]
A --> C[Bats]
A --> D[Cheetah]
A --> E[Humans]
Molecular and Biochemical Evidence
Biochemical similarities among diverse organisms suggest common ancestry.
Observational Evidence: Industrial Melanism
The study of moths in England during industrialisation illustrates natural selection in action.
Adaptive Radiation
Darwin’s Finches
Darwin observed various finch species with different beak shapes on the Galapagos Islands, each adapted to specific diets and habitats.
Australian Marsupials
Marsupials in Australia evolved into different forms, showcasing adaptive radiation.
graph LR
A[Common Marsupial Ancestor] --> B[Kangaroo]
A --> C[Koala]
A --> D[Wombat]
A --> E[Tasmanian Devil]
Convergent Evolution
Similar traits in organisms from different regions due to similar environmental pressures.
Biological Evolution
Variation and Natural Selection
Natural selection acts on variations within a population, leading to the survival of those best adapted to the environment.
Microbial Examples of Evolution
Microbes with shorter life cycles illustrate rapid evolution and adaptation.
Genetic Basis of Adaptation
Adaptive traits have a genetic basis and are inherited by future generations, ensuring the survival of fit individuals.
Mechanism of Evolution
Mutation Theory by Hugo deVries
Mutations are sudden, large changes in the genetic makeup, contributing to evolution.
Types of Natural Selection
- Stabilising Selection: Favouring average traits.
- Directional Selection: Favouring one extreme trait.
- Disruptive Selection: Favouring both extreme traits.
graph LR
A[Average Trait] --> B[Stabilising Selection]
C[Extreme Trait 1] --> D[Directional Selection]
E[Extreme Trait 2] --> F[Disruptive Selection]
Hardy-Weinberg Principle
The Hardy-Weinberg Principle states that allele frequencies in a population remain constant unless influenced by external factors like mutation, gene flow, or natural selection.
pie
title Allele Frequencies
"Allele A": 50
"Allele a": 50
Factors Affecting Hardy-Weinberg Equilibrium:
- Gene migration or flow
- Genetic drift
- Mutation
- Genetic recombination
- Natural selection
A Brief Account of Evolution
Major Milestones in Life's History
- First Cellular Life: About 2,000 million years ago.
- Evolution of Fish: Approximately 350 million years ago.
- Reptiles and Mammals: Emerged after amphibians, dominating Earth for millions of years.
Evolution of Vertebrates
From jawless fish to amphibians, reptiles, and mammals, vertebrate evolution is a story of adaptation and survival.
graph TD
A[Jawless Fish] --> B[Amphibians]
B --> C[Reptiles]
C --> D[Mammals]
Origin and Evolution of Man
Early Primates
Primates like Dryopithecus and Ramapithecus existed around 15 million years ago.
Australopithecus and Homo Habilis About 2 million years ago, Australopithecus lived in East Africa. Homo habilis, the first human-like being, had better tool usage abilities.
Homo Erectus and Neanderthals
Homo erectus, discovered in Java, had a larger brain size and used tools. Neanderthals lived in central Asia and had complex social behaviours.
Modern Homo Sapiens
Homo sapiens emerged in Africa, spreading across continents and developing diverse cultures.
Conclusion and Summary
The origin and evolution of life on Earth are integral to understanding our place in the universe. By studying the evidence for evolution, from fossils to genetic data, we gain insights into the processes that have shaped the diversity of life today.
This comprehensive guide offers detailed notes on evolution for Class 12 students, covering essential topics and concepts to ensure a thorough understanding of the subject.
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