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Class 12 Biology Chapter 7 Evolution
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Evolution
Chapter – 7
GENETICS AND EVOLUTION
Very Short Answer Type Questions
Q.1. When does the earth originated?
Ans : 600 million years ago.
Q.2. What do you mean by ‘theory of spontaneous generation or abiogenesis?
Ans : Aristotle and others believed that life originated spontaneously from inanimate objects and this is called the theory of spontaneous origin.
Q.3. Who propounded the ‘theory of biogenesis’?
Ans : Louis Pasteur.
Q.4. What is protovirus?
Ans : Primordial stage of evolution of virus.
Q.5. What were the raw materials in Miller’s experiment?
Ans : CH₄, NH₃, and H₂,.
Q.6. What were the earliest living beings?
Ans : Bacteria and bacteria like organisms.
Q.7. Who wrote the book ‘origin of species’?
Ans : Darwin.
Q.8. What is the term given to describe evolutionary history of organism?
Ans : Phylogeny.
Q.9. What is paleontology?
Ans : The study of fossil to trace the history of evolution.
Q.10. Who proposed the theory of inheritance of acquired characters?
Ans : Lamark.
Q.11. What do yo mean by era?
Ans : During the formation of the earth layers after layers of sedimentary rock had been deposited over the earth crust formed by igneous rock. There sedimentary layers of rocks have been divided into five distinct stratifications. The time taken for formation of each strata is called an era.
Q.12.· How can you determine the age of a living tree?
Ans : Using radioactive carbon or by making cross section of the main stem at the base and then by counting the annual rings.
Q.13. How can you determine the age of a fossil?
Ans : The sedimentary rock in which the fossil is discovered is tested for the percentage radioactive uranium and lead.
Q.14. Define connecting link by giving example.
Ans : The living organisms having the characters of two different taxonomic categories are called connecting links eg. Protopterus between the bony fish and amphibians, Duck bill platypus is the connecting link between mammals and reptiles.
Q.15. What is atavism?
Ans : It is reappearance or refunctioning of some ancestral organs which have either completely disappeared or are present as vestigial organs. eg. Birth of a human body with a small tail.
Q.16. Give the alternative term of biogenetic law and define what it is.
Ans : The alternative term of biogenetic law is biogenesis. This law states that life arises from pre existing life only. The idea was given by Fransisco Redi (1668).
Q.17. What do you meant by discontinuous distribution?
Ans : When descendants of a common ancestor inhabit different geographical areas and differ from each other it is called discontinuous distribution.
Q.18. What is gene pool?
Ans : Total number of different genes present in all the individuals of a population is called gene pool.
Q.19. When does a species becomes founders to cause founder effects?
Ans : A species becomes a founder when it undergoes the variation process.
(B). Fill Up The Blanks :
Q.1. ___ and ___ tried to create an atmosphere in the laboratory which might have been existed in the primitive earth.
Ans : Stanley Miller and Harold Urey.
Q.2. Polymerization of amino acid results in the formation of _____ molecules.
Ans : Protein.
Q.3. The nictitating membrane or the third eyelid present at the inner corner of human eye is also a _____ organ.
Ans : Vestigial organ.
Q.4. ____ means the origin and development of new living organisms, both plants and animals, on the surface of the earth as a result of slow but continuous change.
Ans : Evolution.
Q.5. _____ provide the missing links in the evolution of the present day flora and fauna.
Ans : Living fossil.
Q.6. In plants, the thorn and tendrils of ___ and ____ represent homology.
Ans : Duranta and Passion flower.
Q.7. _____ is the example of adaptive radiation.
Ans : Finches.
Q.8. Continuous _____ of an organ leads to its reduced efficiency and size and ultimately it disappears.
Ans : Disuse .
Q.9. ____ brought forth the idea of mutation.
Ans : De vries.
Q.10. ____ and _____ one the two key concepts Darwinian theory of Evolution.
Ans : Survival of the fittest, Natural selection.
Q.11. Ontogeny ___ phylogeny.
Ans : Recapitulate.
Q.12. ____ is a connecting link between cartilaginous and bony fishes.
Ans : Protopterus.
Q.13. Genetic drift causes change in gene frequency of_____
Ans : alleles.
Q.14. Atmosphere of the primitive was highly ____ while that of the present earth is highly _____
Ans : Hot, (gaseous), Cool (solid).
(C). Select The True And False:
Q.1. Life first originated on land surface.
Ans : False.
Q.2. Fossils do not form the evidence of evolution.
Ans : False.
Q.3. The most convincing morphological evidence of evolution is provided by the vestigial organ.
Ans : True.
Q.4. Lamarck wrote the book ‘Philosophic Zoologique’ in 1809.
Ans : True.
Q.5. Interspecific struggle occurs among individuals of same species living together.
Ans : False.
Q.6. Hugo de Vries was a Dutch botanist who coined the word mutation in 1901.
Ans : True.
Q.7. Homologous organs are structurally and ontogenetically similar due to common ancestry but have varied function.
Ans : False.
Q.8. Vermiform appendix is not a vestigial organ.
Ans : False.
Q.9. From the protocells or provirus type of particles probably prokaryotic Monera like cells evolved in which organised nucleus was absent.
Ans : False.
Q.10. A. J. Oparin and JBS Haldone advocated the theory of chemical evolution of the origin of life.”
Ans : True.
Q.11. Atmosphere of earth became oxidising with the of cyanobacteria.
Ans : False.
Q.12. Fins and flippers are homologous organs.
Ans : True.
Q.13. Sickle cell anaemia is of selective advantage in malaria prone area.
Ans : True.
Q.14. Amphibians have two chambered heart.
Ans : False.
II. Question for 2 Mark :
Short type Questions :
Q.1. What do you mean by coacervates?
Ans : In the ocean of the primordial earth there originated large molecules such as polysaccharides lipids, proteins, nucleic acids etc. There macromolecules combined in a complex situation to form a cell like structure which in course of further evolution gave rise to primitive cells. These cell-like substances are called coacervates.
Q.2. ‘Archaeopteryx is considered as connecting link between reptiles and birds’. Explain.
Ans : It happens that in the stages of evolution of two or more organisms no continuity is found and a result their evolutionary history remain inconclusive. But by chance if some intermediate form of each organism is discovered which give clue to the evolution of such organisms. These forms are called transitional forms. Archaeopteryx is one such form which shows evolutionary link between birds and reptile. Because it shows the certain characters of both.
Q.3. How do Darwin’s finches illustrate adaptive radiation.
Ans : All living organisms of today are descendent of some common ancestors. They have evolved differently due to the influence of climate, competition, reproductive isolation and so on. They have adapted according to climate, food, geographic location etc. The various finches species which Darwin had seen in Galapagos island were although different from the mainland all had originated from the main land stock, but evolved according to the local situation in the island.
Q.4. What is ‘Theory of special Creation’? Describe briefly.
Ans : People from the ancient time were curious about the origin of creatures. In the ancient time being unaware of scientific enquiry thought that all creatures have originated as they look like and had not gone through any change. This theory is called the Theory of Eternity. This theory is not much different from the theory of special creation. According to it God has created every species and these can never undergo any change.
Q.5. What is the most widely accepted theory of origin of life who proposed it?
Ans : Theory of Biogenesis. It means life originates from life. It over through the theory of special creation.or the theory of eternity. Louis Pasteur had proposed this theory.
Q.6. What are Fossils?
Ans : Fossils are the remains of the past forms of life in parts or whole in which the organic molecules have been replaced by inorganic molecules rendering these indecomposable. Highly compressed form or their cast are found trapped between sedimentary layers of the earth they provide strong evidence of evolution.
Q.7. What is geological time scale?
Ans : The crust of the earth has been formed by deposition of sedimentary rocks formed layers after layers. These layers are called stratification. The geological time period at which these stratification have bcen formed has been determined. These time extends to millions of years in the past. For convenience of determining the age of these stratifications some time periods such as era, period, epoch have been determined. These are called geological time scale.
Q.8. State any two vertebrate body parts that are homologous to human fore limbs.
Ans : Wings of birds and forelimb of monkey.
Q.9. ‘Adaptive ability is inherited’. Justify
Ans : If separated from the main stock and migrate to places other than of its earlier one the organism try to adapt there. It may not be possible to adapt easily as the climate and the food may be different and the type of competition may also be different. Those who survive in the new condition after fully adapting to the changed situation may pass on the adapted character to their offsprings. If offsprings show these adaptive character then it means that the adaptive ability is inherited.
Q.10. What is mutation?
Ans : It means sudden change caused by change of structure of gene or chromosome various causes may be attributed to this. This is unlike slow and continuous change according to Darwin’s theory of evolution. This sudden change is also causes evolution if the change is transmitted to offsprings and is inherited. Generally most mutations are not stable.
Q.11. Explain the term progressive and retrogressive evolution by giving suitable examples?
Ans : Progressive evolution : In which the size of the organism increases eg. height of horse increases from the …. group.
Retrogressive evolution : The evolution in which general degeneration and loss of organ takes place, is called retrogressive evolution. For eg. the number of functional digit reduced from 4 to 1 is known as retrogrennu evolution.
Q.12. What is spontaneous generation theory? Name the scientist who disproved this concept.
Ans : The spontaneous generation theory states that life originated biogenetically from non living decaying and rotting matter like straw mud etc. by spontaneous generation about 3.5 million years ago. This is proposed by Von Helmont (1577-1644).
Q.13. Define biological species.
Ans : The groups of organisms which are morphologically similar and can reproduce among themselves is called a biological species.
Q.14. Explain the term biogenesis?
Ans : Biogenesis means life arises from pre existing life only (omne vivum ex vivo).
Q.15. Mention the concept about mechanisms of biological evolution/speciation according to Devries.
Ans : According to the mutation theory given by De Vries, evolution is a discontinuous and jerky process in which there is a jump from one species to another species so that new species arises from pre existing species in a single generation (macrogenesis).
III. Question for 3 Mark :
Short type Questions :
Q.1. “Embryology provide evidences of organic evolution’. Explain.
Ans : Amongst the evidences of organic evolution, the embryological evidences are found to be most conclusive. If we study the developmental stages from eggs then we will find some similarities in their development than to the adult. Fog example, the study of embryo of fish, frog, lizard, birds, mammals revels that after fertilization, zygote is formed and which is followed by a series of cleavage. The zygote is now called as mórula which is common to all. Again it follows blastula and gastrula stage which is also common to all. The embryo is showing the aquatic mode of life and we can conclude from this study, that all the vertebrate animals are coming from aquatic mode of life. Ontogeny recapitulates phylogeny is widely accepted.
Q.2. Distinguish between :
(a) Homologous organ and Analogous organ.
Ans : Homologous organs are those which show varied function but are structurally similar and have common origin. For example the wing of birds, forelimb of human, forelimb of horse, flipper of whale are all functionally different but structurally and from the point of origin are similar. Analogous organs are functionally similar but structurally dissimilar and from the point of origin also different. For example the wings of butterfly and the wings of bat are functionally similar but have different origin and structure.
(b) Convergent and Divergent evolution.
Ans : Homologous organs show trend of convergent evolution. The forelimb of human, forelimb of horse, the flippers of whale, the wings of bat are all structurally similar and have common origin. But due to change of environment, food, survival strategy these organs have undergone modification and other hand, Analogous organs though structurally and from the point of origin are different but have to perform similar function. The wings of bat and the wings of butterfly, flipper of dolphins, the wings of penguin are such structures. These are example of divergent evolution.
Q.3. Describe briefly about Lamarckism.
Ans : Jean Baptist de Lamarck (1744-1829) proposed an explanation of evolution in 1809. He was a French biologist . His theory was known as theory of inheritance of acquired characters or popularly known as Lamarckism. This scientifically propounded theory of organic evolution was first published in his book “Philosophic Zoologique” in 1809. Although the validity of Lamarckism was questioned by others in later period, it was regarded as the first scientific basis of explanation of evolution that occurs in all forms of life.
Lamarck laid down certain factors which govern the process of organic evolution.
These factors are :
(i) Influence of environment.
(ii) Use and disuse of organs.
(iii) Inheritance of acquired characters.
The environment in which the organisms live influences the life processes of the individual. The environmental change leads to the change of the habit of the organism. The change of habits result into the change of the structures of the body. A particular environment requires greater use of a particular organ or it may require the use of an organ which is not essential in the former individuais. Environment has influence on the morphological characters of an organism which may be later transmitted to the next generation.
According to Lamarck the structure and development of an organ depend on the use of this organ or system. Continuous use of a particular organ to adapt in a particular environment enhances the size and efficiency of this organ. Continuous disuse of an organ leads to its reduced efficiency and size and ultimately it disappears. Such changes in structure during the life time of a particular organism is known as an acquired character. The acquired characters become genetical character and inherited from one generation to the next generation.
Q.4. Do mutation has any significance in evolution? Explain.
Ans : Hugo de vries (1840-1935) was a dutch botanist who coined the 4. word mutation in 1901.
Mutation is a sudden heritable phenotypic change independen of the environmental influence de vries studied the different types of ornamental garden plants called oenothera lamarckiana (evening primrose). de vries observed that all the plants of this species were not the same. Some were different from the others. He noted two new types and named oenothera bevistylis and oenothera longifolia each of which breed true from seed. The original species oenothera lamarckiana and these two new types were then cultured in the botanical garden of Amsterdam de Vries found that several new kinds which can be regarded as new species occurred in the following generations. These new species difference markedly from the next. These new types breed true and were called mutants devries observed that the new species occurred in his culture might be due to some sudden herit able changes.
From the above observation he stated that new species appeared as a result of sudden discontinuous variations rather than by slow but gradual variations. As the mutations were of random occurrence, evolution was also considered to that at random. de Vries was of the opinion that mutants appear from time to time which show gametes are somewhat different from the usual ones of a particular species. Though the mutation theory of de Vries was accepted by magi workers but he could not explain why mutation occur.
Studies on mutation were undertaken by many workers later. The idea of mutation put forwarded by de Vries was found to be different from the present day explanation of mutation. Later studies showed that new types described by de Vries were not true mutants. Latest study reveals that true mutation brings changes in the gene level. Hence genetic characters are changed. The mutation which is found in gametes or genetic level are inherited. The occurrence of true mutation is extremely rare.
Q.5. Discuss the Modern synthetic theory.
Ans : The basic concept of modern synthetic theory is based on Dobzhansky’s (1937) book Genetic and origen of species. The name modern synthetic theory term was given by Julian Huxley is 1942. Many scientists consider Neo-Darwinism as the modern synthetic theory of evolution.
According to those scientists there are different factors which influence the process of organic evolution.
(i) Basic Factors :
(a) Gene mutation.
(b) Change in chromosome structure and number.
(c) Genetic recombination.
(d) Natural selection.
(e) Reproductive isolation.
(ii) Accessory Factors :
(a) Gene migration.
(b) Hybridization.
(c) Genetic drift.
Out of all the 5 basic factors, the first three factors are necessary to develop genetic variations while last two provides the direction to the process of organic evolution.
Q.6. What is adaptive radiation? Give examples.
Ans : The process of evolution of different species in a given geographical area starting from one point and rediating other areas of geography or habitats is called adaptive radiation. Darwin’s finches represent a good example of this phenomenon. Different types of movements in placental mammals and Australian marsupials are other examples. no slt Elephants and tigers are mainly found in Africa and India.
Q.7. List any two factors which could upset the genetic equilibrium of a population.
Ans : According to Hardy-Weinberg’s principle the gene frequency in a population remains unchanged. Genes may flow within the population but the overall gene frequency will remain the same. This is called genetic equilibrium. Genetic equilibrium may be disturbed by two factors only. One, due to mutation and the other due to genetic drift. In an extremely small population repeated interbreeding involves the same gene pool. There is no chance of inflow of new genes. Moreover, there is sufficient chance that none of the individuals carrying a particular allele may mate and reproduce successfully.
The progenies of these individuals will be totally devoid of that particular allele. In this way many alleles may be lost gradually from the population or particular alleles may proportionately increase. Such variation in gene frequency is called genetic drift. As genetic drift causes loss of variability, it has no significance in progressive evolution. However, genetic drift increases variability within species and hence the chance of their survival under changed environment is brighter than a larger population.
Q.8. Why are the wings of a butterfly and that of a bat called analogous?
Ans :The wings of butterfly and wings of bat are termed as analogous. As we knew that the organs which may have different structure or origin, but performing the similar mode of function then it is called as analogous. The structure of bat is not similar to the structure of butterfly and they have different origin of their wings. But in both the cases wings are used to perform the same function i.e. fight hence analogous.
Q.9. “The evolutionary story of moths in England during industrialization reveals that evolution is apparently reversibles’ Discuss.
Ans : In pre-industrial era moths of England were white. They used to rest in trees having lichen which were white. Thus they could avoid detection by birds. But during industrial revolution lichens had vanished due to smoke and dust. The moths then could not hide themselves from predator. As a result they gradually changed their colour from white to blackish so that if they rest on the trunk of licken less trees they could not be detected easily. This is a kind of reversible evolutionary exercise.
Q.10. Discuss briefly the experiment of Miller.
Ans : A number of theories were put forwarded by a number scientists to demonstrate the process of evolution of life. Out of Stanley Miller and Harold Urey is 1953 demonstrated an experiment to establish the chemical origin of life.
They tried to create and atmosphere in the laboratory which might have been existed in the primitive earth. High intensity electric sparks were passed through a mixture of water vapours, methane, ammonia and hydrogen gases which were thought to have constituted the primitive atmosphere (taken in a closed vessel). As a result various organic compounds were formed including the amino acids. The mixture was allowed to stand for several weeks. The solution was then chromatographed. Miller could detect several organic compounds including both carbo-hydrates and amino acids, like glycine and alanine etc. in the mixture. For (1955), Palim and Calvin (1962) and many other were also successful in synthesizing the organic compounds in the laboratory following Miller from the similar elements which probably constituted the primitive atmosphere.
Q.11. What is natural selection? Elucidate two different effects of natural selection on variation of organisms.
Ans : The process by which comparatively better adapted individuals out of a heterogenous population are favoured by nature over the less adapted individuals is called natural selection.
(a) Natural selection causes the progressive changes in gene (v) frequencies i.e. The frequency of adaptive gene increases while the frequency of less adaptive gene decreases.
(b) Those individuals, which are best adapted to the environment, survive longer and reproduce at a higher rate and produce more offsprings rate and produce more offsprings than those which are less adopted.
Q.12. What do you mean by speciation? Name the different form of speciation.
Ans : The origin of a new species from pre-existing species in called the speciation.
The speciation is of the following types:
(A) Gradual Speciation : It is the gradual divergence of population due to the accumulation of variations. It is of two types:
(i) Allopatric Speciation : When an original population becomes separated spatially because of geographic barrier, into two or more groups, then it is called allopatric speciation e.g. Darwin’s finches of Galapagos.
(ii) Sympatric Speciation : It occurs within same geographical area stand within original population and reproductively isolated.e.g pig frog and Gopher frog.
(B) Abrupt speciation : Sudden development of a species is called abrupt speciation. It is of two tipes –
(i) Mulation : Mutation can produce the Libling species which are morphologically similar but ecologically and reproductively isolated eg. Drosophila pseudoobscura and D. Persimilis.
(ii) Hybridization : It is caused by hybrid. e.g. Rapheno brassica.
| Sl. No. | CONTENTS |
| Chapter 1 | Reproduction in Organisms |
| Chapter 2 | Sexual Reproduction in Flowering Plants |
| Chapter 3 | Human Reproduction |
| Chapter 4 | Reproductive Health |
| Chapter 5 | Principles of Inheritance and Variation |
| Chapter 6 | Molecular Basis of Inheritance |
| Chapter 7 | Evolution |
| Chapter 8 | Human Health and Disease |
| Chapter 9 | Strategies for Enhancement in Food Production |
| Chapter 10 | Microbes in Human Welfare |
| Chapter 11 | Biotechnology: Principles And Processes |
| Chapter 12 | Biotechnology and its Applications |
| Chapter 13 | Organisms and Populations |
| Chapter 14 | Ecosystem |
| Chapter 15 | Biodiversity and Conservation |
| Chapter 16 | Bioresources of Assam |
| Chapter 17 | Environmental Issues |
Q.13. In what sense mutation explained by Hugo-de-vries are different from Darwinian variations.
Ans : The followings are the reasons for which mutation is different from the Darwinian variation.
(a) Mulation is a sudden change process which is abruptly taking place while the Darwinian variation process.
(b) Mulation creat and maintain variation within the population is not found in Darwinian variation.
(c) In mutation chromosomal make up, genetic combination may change but in Daminian variation, shape size and colour may changed.
IV. Long Questions for 5 Marks : (Explanatory)
Q.1. How do the photosynthetic organisms evolved? Discuss.
Ans : At the beginning atmosphere was devoid of oxygen the first life- forms were probably anaerobes. They probably depended on organic raw materials in the form of some molecules found on the chemical broth making the sea water. These were most probably chemoheterotrophs or chemoautotrophs. All were anaerobes. They probably ruled the sea between 4280 to 3500 million years ago. They utilised chemical compound to derive might belonged to this group.
Consequence of variation in response to changing need led to evolution of photosynthetic organisms. The early photosynthetic organisms were anaerobic in nature. The photosynthetic anaerobes were primitive bacteria. These bacteria used to frap solar energy but did not produce oxygen because they did not make use of water. The first aerobic photosynthetic organisms probably were some cyanobacteria-like organisms evolved 3300 to 3500 million years ago. They were the earliest oxygen producing photo- autotrophs with the origin of chlorophyll molecules the diversification in organisms had started. The earth began to be green.
With the increasing accumulation of free oxygen in the environment the reducing environment gradually transformed into an oxidising one leading to further changes in life forms and consequent further evolution. As a result of this, the cell organelles like nucleus, mitochondria etc. developed. The eukaryotes emerged in ocean nearly 1,600 million years ago. Further, the aerobic organisms began to oxidise food to liberate energy. Autotrophic organisms being the only type of organisms capable of synthesising food, became the source of food for heterotrophs. The photosynthesis and respiration began to balance each other from the very early age.
Q.2. What is organic evolution? Give the evidences of organic evolution.
Ans : There are different forms of animals and plants in the nature. The development of new complex living organism both plants and animals on the surface of earth as a result of slow but continuous changes. This mechanism is called the organic evolution. The term evolution mean to hardly change from one form to another (Latin e = out + volvere = to roll).
(a) Evidences from Comparative Anatomy and Morphology: Comparative anatomy of animals provides the most extensive evidences of organic evolution. Though the structure and functions of different organs of animals are varied, the basic pattern of organisation are aim the same in a group or a class of animals or plants.
A few examples anatomical similarities are as follows :
(i) Homology : Homologous organs are structurally and ontogenetically similar due to common ancestry but may have varied functions. For example, there appears little similarity between flippers of whale, wings of bats, forelimbs of horse and the hands of human being. All the structures are dissimilar in look and the functions are also quite different. But all these structure possess almost same number of bones, muscles, nerves and blood vessels and their mode of development are also almost similar. All these structures have common origin and are built on the same basic pattern, but due to their adaptation for different functions they are superficially dissimilar. The existence of homologous organs suggests that all these vertebrate animals have inherited the basic structure from 4 common ancestral stock.
- Forelegs of Amphibia
- Flippers of Sea
- Wings of Birds
- Wings of Bat
- Forelegs of Horse
- Hands of Human
(ii) Analogy : They have structural differences but have functional (1) similarities means they are coming from the same environment.
Wings of Bat and wings of Butterfly are the common example of analogous organs.
(iii) Vestigial Organs : The most convincing morphological evidence of evolution is provide by the vestigial organs. Sometimes an organ which is well developed in one group may be present in rudimentary and functionless condition in another group. Such reduced and functionally useless organs are called vestigial organs. Vestigial organs were once functional and fully developed in the ancestral form but have lost their significance and are reduced structurally in the present form.
The presence of all these vestigial organs in different animals can only be explained by the fact that the ancestors of these animals had used these organs. Because of the change of environment or mode of life these organs became nonfunctional and so became reduced in size.
The common vestigial organs of Man are:
(a) Vermiform appendix.
(b) Coccyx.
(c) Nictitating membrane.
(d) Wisdom teeth.
(e) Body hair.
(f) Ear muscle.
(g) Abdominal muscle.
(h) Nipples of Male (Man)
(i) Clitoris of female.
(b) Evidences from Comparative Embryology : The study of the development of an organism from egg to the adult is known as embryology. Amongst the evidences of organic evolution, the embryological evidences are found to be the most conclusive evidences of evolution. It has been observed that the embryos of different groups of animals have many similarities in their development than the adults. For example, the embryonic development of all groups of vertebrates have striking resemblance during their early stage of development. All multicellular animals start their development is a single zygote. The zygote divides mitotically to form the blastula. The cleavage, blastula and gastrula are almost similar in all the groups of vertebrates.
Embryos of all groups of vertebrates possess gill pouches in their early development but; functional gills are found only in fishes and in tadpoles of amphibians. The avian and mammalian embryos possess simple tubular heart and same pattern of aortic arches that are found in fishes. The vertebrate embryos possess notochord which is present only in protochordates.
Why all these structures found only in lower chordates, develop in the embryos of reptiles, birds and mammals? It is because these animals have evolved from a common ancestor.
(c) Evidences from Palaeontological Records or Geological Evidences : Palaeontology means the study of fossils of ancient plants and animals. The direct evidence of organic evolution is provided by fossils. Fossils provide the missing links in the evolution of the present day flora and fauna.
Fossil remains are found deep under the soil. They are therefore have to be excavated carefully. Different types of plant and animal fossils have been discovered in different geological strata. Whenever any kind of fossil is discovered in any strata it becomes necessary to ascertain the geological time at which the organism was in existence. It is also necessary to ascertain its evolutionary position by linking it up wich fossils of related forms found in its lower and upper strata in the same place or in other places. It is also necessary to know whether such fossils have been found in other places and in other geological strata. The period in which the animals or plants were existed can be determined by study of fossil records.
Q.3. What is fossil? How fossils were formed?
Ans : Fossils are the remains of the past. The organic body or to parts under the sedimentary rock undergo change in which the organic molecule were replaced by inorganic molecular and therefore become solid and non decomposable. They are to form impression upon sedimentary rocks. They show evidence of evolution.
Igneous’ rocks formed the original earth crust upon which the layers of soil that sustained life gradually formed. Due to physical and chemical action the igneous rock got warm out. Torrential rain of those days brought down the soil, organic matter and the worn out rocks to sea and other low areas. The debris settled down layer upon layer. The lower layers gradually hardened due to pressure from above layers. These lower layers gradually formed the sedimentary rocks and became fossils. Along with the debris various kinds of organisms also got hurried under the sedimentary rocks. The process of fossilization depends upon environmental condition, physical, chemical and biological action.
Those parts of the plant or animal bodies which were less immune to microbial decomposition became fossils. Those plant or animal parts which were quickly buried and oxygen was not available for decomposition, rapid infiltration of minerals took place which replaced the organic fractions converting the plant or animal parts into fossils. Fossils are highly compressed because of heavy pressure of sedimentary rocks that formed above. Such fossils are without any trace of organic fraction in them and became completely petrified. Other forms of fossils such as cast, impression etc. are also found. Coal, petroleum, limestone, graphite etc. are also some kinds of fossils.
Q.4. Discuss the theory of Natural selection of Darwinism.
Ans : Darwinism : Darwin suggested that the animals always adopt themselves to their environment and to ensure the continuity of their race, they reproduce their own kinds. Those who fail to adopt themselves to their environment perish in due course and the fittest survive ruling over the land. Thus there always prevails some sort of selection in nature and this is known as Natural Selection. He published his monumental work on the “Origin of Species by Natural Selection’ in the book Origin Species.
Basis of Darwinism :
(a) Over production : It is true that, organisms tend to overproduce. If all the offsprings of any species remain alive and reproduce then these will overcrowded the earth within a few years. But it is evident that in nature such enormous increase in number is never occurred. The number of offspring is maintained more or less constant under natural conditions.
(b) Struggle for existence : Because of overproduction of offsprings the struggle for existence occurs among the organisms as food and space remain almost constant.
The struggle for existence may be :
(i) Interspecific : It is the competition among the organisms of different species living together.
(ii) Intraspecific : It is the competition among the individuals of a species.
(iii) Environmental struggle : This is the struggle against the environmental conditions such as drought, flood, etc.
(c) Survival of the fittest : As a result of everlasting competition among organisms, the stronger win and survive, while the weaker are rooted out. Since the unfitted and weak are rooted out, the number of organisms on the earth remains almost constant.
(d) Variation and heredity : The everlasting competition among the (p) organisms has compelled them to change according to conditions so that they can utilize the natural resources and can survive successfully. Therefore, it is difficult to find out two individuals alike. A change of survival value is transmitted to the next generation so that the progeny is still more suited.
(e) Natural selection : After observing the above mentioned fact. Darwin summarised his conclusion under the heading ‘Natural Selection’. He said that due to inheritance, the successive generations tend to become better adapted to their environment. These adaptations are preserved and accumulated and establish new species.As natural selection continues the latter descendants after few generations become markedly distinct from their ancestors. Due to different environmental conditions, from a single ancestral species two or more species may arise.
T.H. Huxley, Herbert Spencer, D.S Jordan and Asa Gray also proposed the same theory.
Q.5. Give the Darwin’s concept of common ancestry and adaptive radiation.
Ans : Darwin’s theory of evolution is based on the fact that all the different types of species of plants and animals found today are the descendants of common ancestors. Gradual variation among them occured due to changes in organism-environment relationship in both time and space. The organism- environment relationship is different for different populations at different places and time. If a homogeneous population living in a particular environment migrates to a new habitat the organism- environment relationship may change. Depending upon the organism-environmental relationship the nature may select out those combination of genes which are better adapted under the given circumstances. In long course of time a few members of the population may show distinct adaptation which is marked by variation of characters.
The environment selects out the better gene combination rom the existing gene pool of the population. The newly adapted individual if become reproductively isolated from its parent population, it establishes itself as a new species and breeds among the newly adapted individual. Such a population which is different, even marginally, from its parent population may migrate to new habitat. If the migrated species overcome competition and adapt to a new geographic area and evolve through further specification, the evolutionary line radiating from the initial population to new geographic area is said to have undergone adaptive radiation.
The adaptive radiation from initial stock first gave rise to races or varieties which had attended the level of species through further adaptation and reproductive isolation. The following two examples will illustrate the concept.
Darwin’s finches are examples of adaptive radiation from a common ancestor. Galapagos islands are situated on the equator some 900 km. west of Ecuador. These islands were originated form volcanic eruption which were later occupied by plants and animals. A few plants and birds originally entered into the islands and later being separated from the parent stock evolved through selection by nature. Darwin had noticed that there were 13 different species of finches Fish were similar to the species in the mainland. The original species migrated to the new lands which provided greatly relaxed selection pressure because of the absence of predators and competitors.
The relative isolation of the islànds permitted the establishment of unique hind races or subspecies. From these had arisen the 13 different species. These species had given rise to more subspecies. But the fact that in the mainland there was only one species. So the 13 species had a common ancestor on the mainland. The marine species of giant iguana wizard similarly arose from terrestrial species to avoid competition on land. The finches also to avoid competition developed different food habit and therefore they occupied different ecological places. Their beaks had evolved to suit different kinds of food.
The homology of forelimbs of mammals illustrates common ancestry. The forelimbs of bat, hale, monkey, pig, horse, mole, ant eater conform to the basic pentadactyl pattern. They were probably originated from common ancestor and evolved in different lines depending upon the need in different ecological niches.
Q.6. Discuss the Hardy Weirnberg’s principle. When the equilibriums get disturbed? Explain briefly.
Ans : Hardy weinberg principle (1908) defined genetic structure of a non- evolving population. It explains that under certain conditions of stability population size is very large, random mating occurs and no allele has selective value then allelic frequencies remain constant from generation to generation in sexually reproducing animals or organisms. If other factors remain constant the frequency of particular genes and alleles will remain constant in a population through generations. Changing gene frequencies would indicate that evolution is taking place. Therefore evolution occurs when the Hardy-weinberg equilibrium or genetic equilibrium is upset. In other words evolution is a departure from Hardy-Weinberg equilibrium.
The dominant alleles do not, infact, replace recessive ones because their proportions do not change, The genotypes are said to be in Hardy-Weinberg equilibrium.
The Hardy-Weinberg principle in algebraic terms is written as an equation. Suppose a population of 100 cats contains 84 black and 16 white cats. In this case, the respective frequencies would be 0.84 (or 84%) and 0.16 (or 16%). The white homozygous (BB) or Heterozygous (Bb) and the recessive character (bb).
Let the letter p designate the frequency of one allele and the latter of the frequency of the alternative allele, Because there are only two alleles, p and q must always equal to 1.
The equation can be expressed as:
(p+q)² = p² + 2pq + q²
(Individuals of BB) (Individuals of Bb) (Individuals of bb)
Sperm Ovum
P = 0.6 (B) P = 0.6 (B)
q = 0.4 (b) q = 0.4 (b)
p² = BB = 0.36 (white)
pq = Bb = 0.24 (white)
+ pq = Bb = 0.24 (white)
+ q² = bb = 0.16 (black)
| Phenotype | White cat | White cat | Black Cat |
| Genotype | BB | Bb | bb |
| Frequency | P² + | Pq + pq | + q² |
| of genotype | 0.36 | 0.48 | 0.16 |
| in population | – | – | – |
| Frequency of | 0.36 + 0.24 | 0.24+ | 0.16 |
| gametes | = 0.6B white | – | = 0.4(b) black |
Q.7. Explain with the help of suitable examples that ‘Anthropogenic actions have caused evolution of species’
Ans : In evolution different group of animals are formed from the common ancestor having different ecological, ethological and reproductive character. The living form have homology and then they develop the analogy. This is also termed as macro evolution which divides a group to many new groups. The newly formed groups has the relationship with ancestral one. For example, the Darwin’s finches, which were found the galapagos island had the similarity although the lived in different places having different characters, establishes the anthropogenic action which causes evolution to the species.
Q.8. What is artificial selection? Is artificial selection can affects the process of natural selection? If it is explain how.
Ans : The process of selecting genetically improved and domesticated plants and animals by man, is called artificial selection. It is also called as 8. man made selection.
Artificial selection is made by man which may affect the natural selection process.
(i) Artificial selection is done by man with desired characters only which may or may not be selected by the nature.
(ii) The selected breeds in Artificial selection are interbreed while the organisms naturally selected may not interbreed.
(iii) Artificial is made by man and can repeated several times.
For example, to obtain the comes with high milk yield, animal breeders takes only those calves which are produced by high yielding varieties of the cows. These calves are interbreed to produce the next generation of cows when the process of artificial selection is repeated for a number of generation, a good breed of high milk yielding cames is produced.
Q.9. ‘Mammals and birds have evolved from reptiles, In what way does a comparative study of their embryology establish the validity of this statement?
Ans : If we study the embryological evidences in the reptiles, birds and mammals, are come to conclusion that birds and mammals are evolved from the reptiles.
(a) The early developmental phases of embryo in mammals and birds have the similarities with reptiles where fertilization always internal.
(b) Reptilian, Birds and Mammalian embryo follows the same cleavage, morula, Blastula and gastrula and finally producing three layered structure.
(c) They have similar notochord, tail, eye and ear rudiment.
(d) In the embryonic stages, birds and mammals all closely related to The reptiles.
(e) The development heart of reptilia which is three chambered leads to avian heart (four chambered) and mammalian (four chambered).
(f) Birds are called the glorified reptiles because of the presence of reptilian characters.
(g) Archaeopteryx establishes the relationship between the reptiles and birds while the duck bill platypus establishes the relationship between the reptiles and mammals.
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