CLASS 12TH BIOLOGY CHAPTER- 7 EVOLUTION NCERT QUICK REVISION NOTES FOR NEET AND CBSE EXAM
CHAPTER 7: EVOLUTION
Big-bang Theory- proposed by Abbe Lemaitre in 1931. About 20 billion years ago on explosion took place which broke the condesend cosmic matter and scattered its fragments into space at an enarmous velocity making a big bang sound.
Origin of life; biological evolution and evidences for biological evolution (paleontology, comparative anatomy, embryology and molecular evidences); Darwin's contribution, modern synthetic. theory of evolution; mechanism of evolution - variation (mutation and recombination) and natural selection with examples, types of natural selection; Gene flow and genetic drift: Hardy-Weinberg's principle; adaptive radiation; human evolution.
Artificial Selection: It is the process carried out by man to select better breeds of plants and animals.
Founders Effect: A genetic drift in human population where a population in a new settlement have different gene frequency from that of the parent population. The original drifted population said to be founder.
Gene Pool: Sum total of all the genes in a population.
Genetic Drift: By chance elimination of genes or any other changes in gene, of certain traits from a population due to migration or death.
Panspermia: Units of life in the form of so called spores, which were transferred to search from outer space, as believed by some scientists.
Saltation : Single step large mutations.
Speciation: It is the formation of new species from the pre-existing ones.
Organic (Biological) Evolution : Changes at the characteristics/features of originisms or groups of such population over a number of generations.
Homologous organs: (These are the result of divergent evolution) these have same basic structure and embryonic origin but perform different functions in different species.
Example:
Plants- Thorns of Bougainvillea and tendrils of Cucurbita
Animals- For limbs of whales, bat, cheetah and human
Analogous organs: (These are the result of convergent evolution) These organs are different in their basic structure and embryonic origin but perform similar functions.
Example:
Animals- Wings of insects and birds
Plants- potato and sweet potato.
Human Evolution: Ramapithecus→Australopithecines Homo habilis→Homo erectus →Homo sapiens →Homo sapiens.
THE THEORIES OF ORIGIN OF LIFE
1. Theory of Special Creation : According to this theory God has created life within 6 days.
2. Theory of Spontaneous Generation: According to this theory life originated from decaying and rotting matter like straw and mud.
3. Panspermiatic Theory: According to this theory life came from space in the form of spores called Panspermia.
4. Modern Theory or Oparin-Haldane Theory: According to this theory life originated upon earth spontaneously from non-living matter. First inorganic compounds then organic compounds were formed in accordance with ever changing environment conditions, this is called chemical evolution. The conditions on earth were high temperature, volcanic storms, reducing atmosphere (without free oxygen) containing methane and ammonia.
Experimental Evidence for abiogenesis (Miller's Experiment): Stanley Miller in 1953 demonstrated in a laboratory that electric discharges can produce complex organic compounds from a mixture of methane, ammonia, water vapours and hydrogen. In this experiment he found that simple organic compounds including some amino acids are formed. In similar experiments others observed the formation of sugar, nitrogen bases, fats and pigments.
He used Spark chamber with two electrodes (to provide Very high-voltage spark for simulation of lightening), a flask for boiling (Simulation for evaporation and circulation) to a temperature of 800°C and a condenser (simulation of raining and, Haldane's Soup). He used mixture of gases like CH4, NH3, H2, and water vapours to simulate conditions of primeval atmosphere.
Molecular evidences: These evidences show common ancestory based on parallel nucleic acid and amino acid sequences as well as universal genetic codes e.g. Human and Chimpanzee DNA is 98.2% same and protein cytochrome c is similar.
Evidences from embryology: These evidences based on comparative development studies of embryo of different vertebrates based upto the observation during embryonic stage of all vertebrates.
The embryo of vertebrates develop a row of gill slit, but these gill slits are functional only in fish.
Ernst Haeckel's biogenetic law: This law states that "ontogeny (development of the embryo) recapitulates phylogeny (development of race)." e.g. Vertebrate head at embronic stage has vestigial gill slits like fishes.
Hugo de vries mutation.
1. Mutation appear all of a sudden
2. Mutations are due to sudden change in genetic make-up
3. Mutations are raw materialof evolution.
Darwinian Variation
1. Darwinian variations are gradual
2. Genes were not known to Darwinian
3. The basis of evolution are continous variations.
Divergent evolution : Development of different functional structures from a common ancestral form is called divergent evolution, c.g. Development of homologous organs.
Convergent evolution : Development of similar adaptive functional structures in unrelated groups of organisms, e.g. Development of analogous organs.
Parallel evolution: When more than one adaptive radiation appeared to have occured in an isolated geographical area then it is called parallel evolution.
e.g. Australian marsupials and placental mammals (corresponding)
Example of Natural Selection
1. Industrial Melanism
2. Restance of insects to pesticides
3. Antibiotic resistance in Bacteria
Industrial Melanism: It is an adaptation where moth living in the industrial area developed melanin pigments to match their body colour to the tree-trunk. Before Industrilisation in England, it was observed that there were more white winged moths on trees than dark-winged moths (melanised moths). After industrialisation (in 1920), there were more dark winged moths in some areas. After industrialisation, trees got covered by smoke. So whitewinged moth were picked up by the birds but dark-winged moths escaped and survived. Thus, industrial melanism supports the evolution by natural selection.
Adaptive radiation: The process of evolution of different species in a geographical area starting from a point and literally radiating to other habitats. is called adaptive radiation.
Examples:
(i) Darwins finches found in Galapagos Island
(ii) Marsupials of Australia.
Evolution of Plants: Unicellular → Multicellular→Algae Rhynia→ type plants →Cycads →Gnetales →Dicot → Monocot.
Hardy-Weingberg principle: The allele frequencies in a population are stable and is constant generation to generation. Sum total of all the allele frequencies is 1.
i.e. p²+2pq+q² = 1 (Where p and q are frequency of Allele A and a)
Factors Affecting Hardy-Weinberg Equilibrium: Gene migration, Genetic drift, Mutations, Recombination, Natural Selection.
(i) Over population
(ii) Limited food and space
(iii) Struggle for Existence
(iv) Variations
(v) Natural Selection (Survival of the fittest)
(vi) Inheritance of useful variation
(vii) formation of new species.
Artificial Selection : (Selective breeding)-Crop plants developed from wild mustard eg. cabbage, kohlrabi, kali, broccoli, cauliflower etc.
Three types of Natural selection.
(i) stabilising selection (Balancing Selection)
(ii) Directional Selection (Progressive Selection)
(iii) Dibruptive Selection (Diver sifying Selection)
BRIEF ACCOUNT OF EVOLUTION
¶ 2000 mya : first cellular forms of life appeared on earth
invertebrates formed
¶ 500 mya : invertebrates formed
¶ 350 mya : jawless fish evolved probably, fish with stout and strong fins evolved which can move on lands as well as go back to water.
¶ 320 mya : Sea weeds and few plants existed probably.
¶ In 1938 : Fish caught in south Africa happened to be a coelacanth which was thought to be extinct. These animals are called lobefins (evolved into first amphibians)
¶ 200 mya : Some of land reptiles went back into water to evolve into fish like reptiles e.g. Ichthyosaurs. Land reptiles were Dinosaurs. Biggest Dinosours Tyrannosaurus rex (20 feet in height, have huge dagger like teeth.)
¶ First mammals were like shrews-They were small sized, viviparous intelligent.
EVOLUTION OF MAN :
About 15 mya, primates called Dryopithecus and Ramapitheus were existing.
Dryopithecus: Were more ape-like, live in Asia, Africa and Europe. Walk semierect, Hands & Skull were monkey like.
Ramapithecus: First man-like, walk straight on legs, not taller than 4 feet.
Australopithecines: 2 mya, lived in east african grassland, hunted with stones, ate fruits, Teeth larger.
Homo habilis: 2 mya, brain capacity 650-800cc, did not eat meat, dentition like humans.
Homo erectus : 1.5 mya, brain capacity 900cc, ate meat, walk erect.
Homo sapiens: 75000-10000 years ago., in Africa, and spread to all parts of world.
Neanderthal man: 40,000-1,00,000 years ago, brain capacity 1400cc, broad forehead, lives in caves, use hides to protect their bodies.
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