EVOLUTION Class XII Biology based on NCERT text book .pptx
- 1. EVOLUTION Dr. Rama Kant Upadhyay
- 2. ORIGIN OF LIFE Big Bang Theory • Singular huge explosion • Expansion of the universe • Lowering of temperature • Formation of Hydrogen and Helium • Condensation of gases due to gravity • Formation of galaxies • Solar system • Milky Way galaxy • Earth: formed about 4.5 billion years back. • No atmosphere on early earth • Water vapour, CH4, CO2 and NH3 released from molten mass covered the surface. • The UV rays (sun) broke up H20 into H and O2 and the lighter H2 escaped. • O2 combined with NH3 and CH4 to form H20, CO2 etc. • The O3 layer formed. • As it cooled, the water vapor fell as rain, to fill all the depressions and form oceans. • Life appeared 500 million years after the formation of earth, i.e., almost four billion years back.
- 3. VARIOUS BELIEFS Panspermia: Early Greek thinkers thought units of life called spores were transferred to different planets including Earth. Theory of spontaneous generation: life came out of decaying and rotting matter like straw, mud, etc. Theory of biogenesis: Louis Pasteur demonstrated that life comes only from pre-existing life. https://microbenotes.com/louis-pasteur-and-his-contributions/ Louis Pasteur
- 4. • first form of life could have come from pre-existing non-living organic molecules (e.g. RNA, protein, etc.) • formation of diverse organic molecules from inorganic constituents. Oparin and Haldane Chemical Evolution • Miller and Urey experiment provides evidence for the origin of life from nonliving matter. • The Primitive atmosphere of Earth was reducing and had high temperatures, volcanic storms containing CH4, NH3, H2, etc. • He created electric discharge in a closed flask containing CH4 , H2 , NH3 and water vapour at 8000C. Miller observed formation of amino acids. • In similar experiments others observed, formation of sugars, • nitrogen bases, pigment and fats. • They hypothesize that the simple molecules combined and formed complex molecules that served as the precursors of life on earth in a reducing environment. S.L. Miller and Urey Experiment Analysis of meteorite content also revealed similar compounds indicating that similar processes are occurring elsewhere in space.
- 5. The first non-cellular forms of life could have originated 3 billion years back. They would have been giant molecules (RNA, Protein, Polysaccharides, etc.). The first cellular form of life did not possibly originate till about 2000 million years ago. These were probably single-cells. All life forms were in water environment only. the first form of life arose slowly through evolutionary forces from non-living molecules
- 6. Charles Darwin • father of evolution • sail ship, H.M.S. Beagle • Book- origin of species • Theory of natural selection (adaptation and speciation) • Survival of the fittest (reproductive fitness) • Darwin finches • Branching descent and natural selection are the two key concepts • of Darwinian Theory of Evolution • Thomas Malthus on populations influenced Darwin. Natural selection occurs in the following four ways: • Variation • inheritance • A high rate of growth of the population • Darwin defined evolution as "descent with modification," the idea that species change over time, give rise to new species, and share a common ancestor. • Differential survival and reproduction Alfred Wallace, a naturalist who worked in the Malay Archipelago had also come to similar conclusions around the same time. wikipedia.org
- 7. WHAT ARE THE EVIDENCES FOR EVOLUTION? Fossils Comparative Anatomy Embryonic Development • Embryonic development - Proposed by Ernst Heckel • based upon the observation of certain features during the embryonic stage common to all vertebrates that are absent in adults. • For example- the embryos of all vertebrates including humans develop a row of vestigial gill slits just behind the head but it is a functional organ only in fish and not found in any other adult vertebrates. • Disapproved by - Karl Ernst von Baer. He noted that embryos never pass through the adult stages of other animals.
- 8. shows similarities and differences among organisms of today and those that existed years ago. Comparative anatomy and morphology • similar structure in different organisms but perform different functions. • shows a common ancestry. • One species gave rise to many other species. • divergent evolution • Examples: the forelimbs of a human, cheetah, whale, and wings of a bat. Vertebrate hearts or brains. Plants: thorn and tendrils of Bougainvillea and Cucurbita • different anatomy but perform similar functions • different species evolved and adapted to a particular environment. • convergent evolution. • Examples:- Wings of butterflies and birds Wings of bats and birds: The wings of birds have feathers for flight whereas, bats have wings made of stretched skin and lack feathers. Eye of the octopus and mammals Flippers of Penguins and Dolphins Sweet potato (root modification) and potato (stem modification) Homologous organs Analogous organs similarities in proteins and genes performing a given function among diverse organisms give clues to common ancestry. These biochemical similarities point to the same shared ancestry as structural similarities among diverse organisms.
- 9. WHAT IS ADAPTIVE RADIATION? • Darwin • Finches (small black birds) in Galapagos Islands. • Change of beak shape due to change in feeding habit from original herbivores to carnivores. • This process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats) is called adaptive radiation • Australian marsupials: Several marsupials, each different from the other evolved from an ancestral stock, but all within the Australian island continent. convergent evolution : When more than one adaptive radiation appears to have occurred in an isolated geographical area (representing different habitats) Placental mammals in Australia also exhibit adaptive radiation in evolving into varieties of such placental mammals each of which appears to be ‘similar’ to a corresponding marsupial (e.g., Placental wolf and Tasmanian wolf-marsupial).
- 10. • Use and disuse of organ • Giraffes https://www.geeksforgeeks.org/lamarckism-theory/ organisms can acquire new traits during their lifetime and pass them on to their offspring.
- 11. MECHANISM OF EVOLUTION Hugo deVries based on his work on evening primrose brought forth the idea of mutations Darwin De Vries Minor variation cause mutation Mutations are random Variations are small and directional directionless Evaluation is gradual Evolution is caused by sudden mutation
- 12. HARDY-WEINBERG PRINCIPLE Allele frequencies in a population are stable and is constant from generation to generation.in the absence of other evolutionary influences. The gene pool (total genes and their alleles in a population) remains a constant. This is called genetic equilibrium. Sum total of all the allelic frequencies is 1 (p=q)2 = 1 p2 + 2pq + q2 = 1 p2= dominant homozygous frequency (AA) 2pq = heterozygous frequency (Aa) q2 = recessive homozygous frequency (aa) Factors affecting Hardy-Weinberg equilibrium • Gene migration or gene flow • Genetic drift • Mutation • Genetic recombination • Natural selection • A group of individuals separates from a larger population to form a new group. • The original drifted population becomes founders The founder effect
- 13. Diagrammatic representation of the operation of natural selection on different traits Stabilizing Directional Disruptive
- 14. A BRIEF ACCOUNT OF EVOLUTION evolution of plant forms through geological periods • About 2000 mya the first cellular forms of life appeared on Earth. • Some of these cells could release O2. • Slowly single-celled organisms became multi-cellular life forms. • About 500 mya, invertebrates were formed and active. • Jawless fish probably evolved around 350 mya. Seaweeds and a few plants existed probably around 320 mya. • We are told that the first organisms that invaded land were plants. • They were widespread on land when animals invaded the land. • Fish with stout and strong fins could move on land and go back to water. This was about 350 mya. • In 1938, a fish caught in South Africa happened to be a Coelacanth which was thought to be extinct. These animals called lobefins evolved into the first amphibians that lived on both land and water. • these were ancestors of modern-day frogs and salamanders. • The amphibians evolved into reptiles. • They lay thick-shelled eggs that do not dry up in sun unlike those of amphibians.
- 15. Representative evolutionary history of vertebrates through geological periods • In the next 200 million years, reptiles dominated on earth. Like the dinosaurs • Giant ferns (pteridophytes) were present • Some land reptiles went back into the water to evolve into fish- like reptiles probably 200 mya (e.g. Ichthyosaurs). • The biggest dinosaurs: Tyrannosaurus rex (20 feet in height). • About 65 mya, the dinosaurs suddenly disappeared from the earth. • Small-sized reptiles of that era still exist today. • The first mammals were like shrews. Their fossils are small- sized. • Mammals were viviparous. • When reptiles came down mammals took over this earth. • There were in South America mammals resembling horses, hippopotamuses, bears, rabbits, etc. • Continental drift; when South America joined North America, these animals were overridden by North American fauna. • Due to the same continental drift pouched mammals of Australia survived because of lack of competition from any other mammal. • some mammals live wholly in water. Whales, dolphins, seals and sea cows
- 16. Dryopithecus Ramapithecus Australopithecus (African ape man) Homo habilis Neanderthal man (Homo sapiens neanderthalensis) Homo Sapiens Sapiens (Cro-Magnon man) The oldest fossil was discovered from South Africa. It inhabited 25 mya. They have characters of both man and apes. This represents common ancestry. More Ape like They are considered as forerunners of hominids and are on the direct line of human evolution and represent the first man-like primates. More man like They were hairy and walked like gorillas and chimpanzees. Few fossils of man-like bones have been discovered in Ethiopia and Tanzania Two mya, lived in East African grasslands. They hunted with stone weapons but essentially ate fruit. first human-like being the hominid, The brain capacities- 650-800cc. They probably did not eat meat Fossils discovered in Java in 1891 Homo erectus about 1.5 mya, large brain around 900cc, probably ate meat. brain size of 1400cc, 1,00,000-40,000 years back, hides to protect their body and buried their dead. lived in near east and central Asia arose in Africa and moved across continents and developed into distinct races • Pre-historic cave art developed about 18,000 years ago. • One such cave paintings by Pre- historic humans can be seen at Bhimbetka rock shelter in Raisen district of MP. • Agriculture came around 10,000 years back and human settlements started. ORIGIN AND EVOLUTION OF MAN
- 17. THANK YOU! Source: NCERT Textbook, Google images