Evolution PDF

Evolution is an orderly change from one form to another. Evolutionary Biology is the study of evolutionary history of life forms. ORIGIN OF LIFE - Big Bang Theory states that universe originated about 20 5. Theory of chemical evolution:...

Evolution is an orderly change from one form to another. Evolutionary Biology is the study of evolutionary history of life forms. ORIGIN OF LIFE - Big Bang Theory states that universe originated about 20 5. Theory of chemical evolution: Proposed by Oparin & billion years ago by a singular huge explosion. Haldane. It states that, the first form of life was originated - The earth was formed about 4.5 billion years ago. from non-living inorganic & organic molecules such as - There was no atmosphere on early earth. Water vapour, CH4, CH4, NH3, H2O, sugars, proteins, nucleic acids etc. i.e. CO2 & NH3 released from molten mass covered the surface. “Abiogenesis first, but biogenesis ever since”. - The UV rays from the sun broke up water into H2 and O2. Urey-Miller experiment - Oxygen combined with NH3 & CH4 to form water, CO2 etc. - Harold Urey & - The ozone layer was formed. As it cooled, the water vapour Stanley Miller fell as rain to form oceans. experimentally - Life appeared almost four billion years ago. proved theory of THEORIES OF ORIGIN OF LIFE chemical 1. Theory of spontaneous generation (Abiogenesis): It evolution. They states that, life came out of decaying and rotting matter created a like straw, mud etc. condition like that Louis Pasteur disproved this theory. He demonstrated of primitive earth that life comes only from pre-existing life. (i.e. high He showed that life did not come from killed yeast in a temperature, closed pre-sterilized flask. But in an opened flask, life volcanic storms, (microbes) appeared. reducing atmosphere with CH4, NH3, H2O, H2 etc). 2. Biogenesis: Proposed by Francisco Redi, Spallanzani & - They made electric discharge in a closed flask containing Louis Pasteur. It states that, life originates from pre- CH4, NH3, H2 and water vapour at 800o C. As a result, some existing life. But it does not explain origin of first life. amino acids are formed. 3. Cosmic theory (Theory of Panspermia): It states that, - In similar experiments, others observed formation of the units of life (spores) were transferred to different sugars, nitrogen bases, pigment and fats. planets including earth. First non-cellular forms of life originated 3 billion years ago. 4. Theory of special creation: It states that, living things They were self-replicating metabolic capsule containing were created by some supernatural power (God). RNA, proteins, Polysaccharides etc. EVIDENCES FOR EVOLUTION 1. Paleontological evidences similar structure and origin but different functions. This Paleontology is the study of fossils. phenomenon is called Homology. Fossils are remnants of life forms found in rocks (earth crust). - E.g. Human hand, Whale’s flippers, Bat’s wing & Cheetah’s They are written documents of evolution. foot. These forelimbs have different functions but similar Significance of fossils: anatomical structures such as bones (e.g. humerus, radius, a. To study phylogeny (evolutionary history or race history). ulna, carpals, metacarpals & phalanges). E.g. Horse evolution. - Homology is also seen in heart, brain etc. b. To study the connecting link between two groups of - Homology in plants: E.g. Thorns of Bougainvillea and organisms. E.g. Archaeopteryx. tendrils of Cucurbita. c. To study about extinct animals. E.g. Dinosaurs. - The origin of homologous organs is due to Divergent d. To study about geological period by analysing fossils in evolution. It is the evolution by which related species become less similar to survive and adapt in different different sedimentary rock layers. The study showed that environmental condition. life forms varied over time and certain life forms are restricted to certain geological time spans. - Homology indicates common ancestry. b. Analogous organs 2. Morphological & Anatomical evidences These are the organs having similar function but different Comparative anatomy and morphology shows that different structure & origin. This phenomenon is called Analogy. E.g. forms of animals have some common structural features. This Wings of insects (formed of a thin flap of chitin) and wings can be explained as follows: of birds (modified forelimbs). a. Homologous organs Eyes of Octopus (retina from skin) and mammals (retina - Homologous organs are the organs having fundamentally from embryonic brain). 1  Flipper of Penguins and Dolphins. 5. Embryological evidences Sweet potato (modified root) & Potato (modified stem). - Proposed by Ernst Haeckel. Trachea of insects (from ectoderm) and lungs of - He observed that all vertebrate embryos have some vertebrates (from endoderm). common features that are absent in adult. Origin of analogous organs is due to Convergent evolution. - E.g. all vertebrate embryos (including human) develop It is the evolution by which unrelated species become more vestigial gill slits just behind the head. But it is functional similar to survive and adapt in similar environmental condition. only in fish and not found in other adult vertebrates. 3. Adaptive radiation (Biogeographical - However, Karl Ernst von Baer rejected this proposal. He evidences) noted that embryos never pass through the adult stages of Adaptive radiation (evolution by adaptation) is the evolution other animals. of different species from an ancestor in a geographical area 6. Evidences for evolution by natural selection starting from a point. It is a type of divergent evolution. E.g. Natural selection is the process in which organisms with better o Darwin’s finches favourable & heritable variation are survived and reproduced. in Galapagos Some evidences are given below: Islands. Industrial melanism: In England, before industrialization o Australian (1850s), there were more white-winged moths (Biston marsupials betularia) on trees than dark winged or melanised moths (Marsupial (Biston carbonaria). After industrialization (1920), more radiation). dark-winged moths and less white winged moths were o Placental mammals in Australia. developed. When more than one adaptive radiation is appeared in an Reason: isolated geographical area, it results in convergent evolution. Before industrialization: There was white lichens covered E.g. Australian Marsupials and Placental mammals. the trees. In that background, white winged moths survived Placental mammals Australian Marsupials but dark winged moths were picked out by predators. Mole Marsupial mole After industrialization: The tree trunks became dark due Ant eater Numbat (Ant eater) Mouse Marsupial mouse to industrial smoke and soot. No growth of lichens. So Lemur Spotted cuscus white winged moths did not survive because the predators Flying squirrel Flying phalanger identified them easily. Dark winged moth survived because Bobcat Tasmanian tiger cat of suitable dark background. Wolf Tasmanian wolf Development of resistant varieties in organisms against 4. Biochemical evidences herbicides, pesticides, antibiotics or drugs etc. - Organisms show similarities in proteins, genes, other These are the examples for natural selection by biomolecules & metabolism. It indicates common ancestry. anthropogenic action (evolution due to human activities). THEORIES OF BIOLOGICAL EVOLUTION Lamarckism (Theory of Inheritance of o Branching descent: It explains that all organisms are Acquired characters) modified descendants of previous life forms. o Natural selection: Consider a bacterial colony A growing It is proposed by Lamarck. It states that evolution of life forms on a given medium. If the medium composition is changed, occurred by the inheritance of acquired characters. only a part of the population can survive under new Acquired characters are developed by use & disuse of organs. condition. This variant population (B) outgrows the others o Evolution by use of organs: E.g. Long neck of giraffe is and appears as new species, i.e. B is better than A under due to continuous elongation to forage leaves on trees. This new condition. Thus, nature selects for fitness. acquired character was inherited to succeeding generations. Natural selection is based on the following facts: o Evolution by disuse: E.g. Disappearance of limbs in snakes. Heritable minor variations: It is either beneficial or This theory was eliminated out because it is proved that the harmful to the organisms. characters are inherited only through genes. Overproduction: Population size grows exponentially Darwinism (Theory of Natural selection) due to maximum reproduction (E.g. bacterial population). - Proposed by Charles Darwin. Limited natural resources: Resources are not increased - It was based on observations during a sea voyage in a sail in accordance with the population size. ship called H.M.S. Beagle. Struggle for existence: It is the competition among - Alfred Wallace (a naturalist worked in Malay organisms for resources so that population size is limited. Archepelago) had also come to similar conclusions. Survival of the fittest: In struggle for existence, - Work of Thomas Malthus on populations influenced Darwin. organisms with beneficial variations can utilize resources Darwinism is based on 2 key concepts: better. Hence, they survive and reproduce. This is called 2  Survival of the fittest. It leads to a change in population (evening primrose) and believed that evolution takes place characteristics and new forms appear. through mutation and not by minor variation. Darwin ignored about origin of variation and mechanism of - Darwinian variation is minor, slow and directional. It evolution or speciation. results in gradual evolution. MECHANISM OF EVOLUTION - Mutational variation is sudden, random & directionless. Here, speciation is by saltation (single step, large mutation). - Hugo de Vries proposed Mutation Theory of evolution. - Mutation is the origin of variation for evolution. - He conducted experiments on Oenothera lamarckiana HARDY-WEINBERG PRINCIPLE - It states that allele frequencies in a population are stable c. Mutation: It results in formation of new phenotypes. Over and is constant from generation to generation in the few generations, this leads to speciation. absence of disturbing factors. d. Genetic recombination: Reshuffling of gene combinations - The gene pool (total genes and their alleles in a population) during crossing over resulting in genetic variation. remains a constant. This is called genetic equilibrium e. Natural selection: It is 3 types. (Hardy-Weinberg equilibrium). Stabilizing selection: Here, more individuals acquire - Sum total of all the allelic frequencies = 1 mean character value and variation is reduced. - E.g. Consider, in a diploid, p & q are the frequencies of Directional selection: Individuals of one extreme (value alleles A & a respectively. other than mean character value) are more favoured. Frequency of AA = p2 Disruptive selection: Individuals of both extremes Frequency of aa = q2 (peripheral character value at both ends of the Frequency of Aa = 2pq distribution curve) are more favoured. Hence p2 + 2pq + q2 = 1 [binomial expansion of (p+q)2] Change of frequency of alleles in a population disturbs Hardy- Weinberg equilibrium. This change is due to evolution. Factors affecting Hardy-Weinberg equilibrium a. Gene migration: Gene flow from one population to another. Here gene frequencies change in both populations. Gene flow occurs if migration happens multiple times. b. Genetic drift: The gene flow by chance causing change in frequency. Sometimes, the change in frequency is so different in the new sample of population that they become a different species. The original drifted population becomes founders and the effect is called founder effect. A BRIEF ACCOUNT OF EVOLUTION The geological time scale includes 4 eras: Proterozoic, In 1938, a lobe-fin called coelacanth fish was caught in Palaeozoic, Mesozoic & Cenozoic. South Africa which was thought to be extinct. 1. Proterozoic era: 2500 - 541 million yrs ago (mya) - 320 mya: Sea weeds and few plants were existed. - 2000 mya: First cellular forms of life appeared. - Amphibians evolved to reptiles. They lay thick-shelled eggs (do not dry up in sun). - Some of the cells had the ability to release O2 as the light reaction in photosynthesis. - Giant ferns (Pteridophytes) were present but they all fell - Single celled organisms became multicellular organisms. to form coal deposits slowly. 2. Palaeozoic era (540 - 252 mya) 3. Mesozoic era (252 - 66 mya) - It has 6 periods: Cambrian (540 - 490 mya), Ordovician - Age of reptiles and gymnosperms. (490 - 443 mya), Silurian (425 mya), Devonian (405 mya), - It has 3 periods: Triassic (230 mya), Jurassic (208 mya) & Carboniferous (360 mya) & Permian (285 mya). Cretaceous (144 mya). - 500 mya: Invertebrates were formed. - 200 mya: Some of the land reptiles went back into water to - 450 mya: First land organisms (plants) appeared. evolve into fish-like reptiles (E.g. Ichthyosaurs). - 400 mya: Arthropods invaded the land. - The land reptiles were dinosaurs (Tyrannosaurus rex, - 350 mya: Jawless fishes were evolved. Triceratops, Stegosaurus, Brachiosaurus etc.) Lobefins (stout & strong finned fishes) could move on land T. rex was the largest dinosaur (20 feet in height, huge and go back to water. They evolved to first amphibians fearsome dagger-like teeth). (ancestors of modern day frogs & salamanders). - Toothed birds were emerged. 3  4. Cenozoic era (66 - 0 mya) Africa. Height up to 4 feet. This belief is based on fossils of - Age of Mammals & Angiosperms. man-like bones found in Ethiopia & Tanzania. - It has 2 periods: Tertiary (66 mya) & Quaternary (2 mya 2 mya: Australopithecus. Lived in East African grass - Age of man). lands. Hunted with stone weapons. Ate fruits. - 65 mya: Dinosaurs suddenly disappeared. Some say Homo habilis: First human-like being (hominid). climatic changes killed them. Some say most of them Brain capacity: 650-800 cc. Did not eat meat. evolved into birds. 1.5 mya: Homo erectus (Java man). Large brain (900 cc). - First mammals were shrew-like. Their fossils are small sized. Ate meat. - In South America, there were mammals resembling horse, 1 lakh - 40,000 yrs ago: Homo neanderthalensis hippopotamus, bear, rabbit etc. Due to continental drift, when (Neanderthal man). South America joined North America, these animals were Brain capacity: 1400 cc. Lived in East & Central Asia. Used overridden by North American fauna. hides to protect their body. Buried their dead. - Due to continental drift, Australian marsupials survived 75,000 - 10,000 yrs ago (ice age): Homo sapiens (Modern because of lack of competition from any other mammals. man). ORIGIN AND EVOLUTION OF MAN Pre-historic cave art developed about 18,000 years ago. E.g. Cave paintings at Bhimbetka rock shelter in Raisen district 15 mya: Dryopithecus & Ramapithecus. of Madhya Pradesh. Hairy. Walked like gorillas & chimpanzee. Agriculture & settlements: 10,000 years ago. Dryopithecus: ape-like. Sequence of Human evolution: Ramapithecus: man-like. Dryopithecus → Ramapithecus → Australopithecus → Homo 3-4 mya: Man-like primates walked up right in eastern habilis → H. erectus → H. neanderthalensis → H. sapiens 1. Match the following: MODEL QUESTIONS A B C Charles Darwin Chemical evolution Use and disuse of organs Lamarck Natural selection Abiogenic origin of life in ocean Hugo de Vries Biogenesis Oenothera lamarckiana Louis Pasteur Inheritance of acquired characters Survival of the fittest Oparin & Haldane Mutation Disproved theory of spontaneous generation 2. Analyze the relationship between first two words and fill the fourth place. a. Homology: Divergent evolution Analogy: ……………….. b. Pisum sativum: Mendel Oenothera lamarckiana: ……………… 3. Classify the following points into two categories. Give suitable titles. Random & directionless, Minor variation, Gradual evolution, Slow & directional, Large variation, Speciation by saltation 4. A bacterial infection was effectively controlled by using a specific antibiotic for a long time. But now- a- days this antibiotic is not found to be so effective. Give a scientific explanation for this phenomenon based on evolution. 5. Hardy- Weinberg Principle has a great contribution in population genetics. a. State Hardy- Weinberg Principle. b. What are the factors affecting genetic equilibrium? c. What is meant by Founder effect? 6. Select the correct order a. Paleozoic era → Proterozoic era → Mesozoic era → Coenozoic era b. Mesozoic era → Proterozoic era → Coenozoic era → Paleozoic era c. Proterozoic era → Paleozoic era → Mesozoic era → Coenozoic era d. Coenozoic era → Paleozoic era → Mesozoic era → Proterozoic era 7. Prepare a flowchart showing the evolution of man. 4