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  1. Evolution

  2. I. History of Life on Earth

  3. I. History of Life A. Early History of Earth I. Early earth was inhospitable • hot, with many volcanoes • little free oxygen and lots of carbon dioxide • other gases present: nitrogen, methane, ammonia, hydrogen and water vapor

  4. I. History of Life B. History in Rocks • Fossils are clues to the past • Any trace of a species that once lived • can infer the structure of the organisms, what they ate, what ate them, and the environment that they lived in • Paleontologists- detectives to the past • scientists who collect, study and classify fossils

  5. I. History of Life • Fossils occur in sedimentary rock • sedimentary rock is formed when exposure to rain, heat, wind and cold breaks down existing rock into small particles of sand, silt and clay. • The particles are carried by streams and rivers into lakes or seas where they eventually settle to the bottom. • As layers of sediment build up over time, dead organism may also sink to the bottom and become buried. • The weight of layers of sediment gradually compresses the lower layers and along with chemical activity, turns into rock

  6. I. History of Life • Non-rock fossils • Fossils can be found in ice • Ex. Woolly Mammoth preserved in ice • Fossils can be found in amber • Organisms preserved in amber • Amber is a form of tree resin—exuded as a protective mechanism against disease and insect infestation—that has hardened and been preserved in the earth’s crust for millions of years

  7. I. History of Life C. Age of a fossil • Relative Dating • oldest fossils are in deepest layers • paleontologists can compare fossils with that of older fossils

  8. I. History of Life C. Age of a Fossil • Radiometric Dating • Use of radioactive isotopes in rocks to date fossils • The technology of radiometric dating provides evidence that the earth is at least 4.5 billion years old • Certain elements convert to other elements at known rates, which can be measured, thus revealing the age of the specimen • One half Potassium40 decays to Argon40 in about 1.3 billion years • Carbon 14 decays to half of its original amount in 5730 years

  9. Common Isotopes used to date Geologic Materials

  10. Bacteria were the earliest life Formed colonies called stromatolites (age 3.5 billion years old) Best colonies in Australia

  11. II. Origins of Life

  12. II. Origins of Life A. Origins: The Early Ideas • Spontaneous generation—non-living material can produce life • Disproved by Redi experiment meat and maggots

  13. II. Origins of Life • Disproved by Pasteur—S flask experiment • boils broth in S flask • broth is free of microorganisms for a year • removes curved neck • broth is “teeming” with microorganisms • Biogenesis—living comes from living things.

  14. II. Origins of Life B. Modern Ideas • Oparin—suggested sun, lightning, and molecules such as water vapor, carbon dioxide, nitrogen, methane and ammonia formed a “primordial soup” that was the beginning of simple organic molecules

  15. II. Origins of Life • Miller and Urey—1953-1954 • Tried to answer the question by simulating conditions on the early Earth • Filled flask with hydrogen, ammonia, methane, and water = atmosphere • They passed electric sparks through the mixture to simulate lightning • Within a few days amino acids were present—the building blocks of protein

  16. II. Origins of Life

  17. II. Origins of Life • Sidney Fox—showed how sort chains of amino acids could cluster to form protocells • Experiments like Miller and Urey’s are currently studied at major universities (i.e. Georgia Tech, U Michigan

  18. II. Origins of Life C. Evolution of Cells (based on fossil record) • First true cells—were probably prokaryotic, heterotrophic and anaerobic • single celled—no nucleus • consumed food for energy • did not need oxygen to survive • Then came chemosynthetic organisms • Then autotrophs—were probably archaebacteria that live in harsh environments • Next came photosynthetic prokaryotes—releases oxygen into atmosphere

  19. II. Origins of Life • Endosymbiotic theory • Proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms—Lynn Margulis of Boston University

  20. II. Origins of Life Endosymbiotic Theory Explained: • Mitochondria and chloroplasts contain DNA similar to bacterial DNA. • Mitochondria and chloroplasts have ribosomes whose size and structure resemble those of bacteria • Like bacteria, mitochondria and chloroplasts reproduce through binary fission • Eukaryotic cells evolved from prokaryotic cells

  21. Endosymbiotic Theory ENDO = Into Symbiosis = relationship of two organisms living close together According to the theory of endosymbiosis eukaryotic cells evolved when aerobic eubacteria either infected or were engulfed by a larger host cell and later established a symbiotic relationship

  22. Natural Selection and Evidence for Evolution

  23. History of the Theory of Evolution Darwin’s Role http://evolution.berkeley.edu/evosite/history/index.shtml

  24. III. Natural Selection and Evidence for Evolution A. Charles Darwin—credited with the Theory of Evolution • Scientists, including Darwin, used fossils to explain that organisms have changed over time • Darwin and HMS Beagle • At age 22, Darwin sailed around the world, trip took 5 years • Ship’s naturalist—he collected specimens and note of the diversity he saw

  25. Galapagos Islands

  26. III. Natural Selection and Evidence for Evolution • Darwin in the Galapagos • Group of islands off the coast of South America • Noted that the animals were unique but similar to the species he had seen elsewhere • Giant tortoises had differences in shell depending on which island they inhabited • Marine iguanas could swim and eat algae • Finches had many different size beaks depending on the type of food they ate

  27. III. Natural Selection and Evidence for Evolution • Darwin Continues his Studies • Lamarck proposed a theory about evolution in the year Darwin was born called Use and Disuse Theory • Proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime • These acquired traits then could be passed on to their offspring

  28. III. Natural Selection and Evidence for Evolution How do we know Lamarck’s explanation is false?

  29. III. Natural Selection and Evidence for Evolution • Darwin continued to look for explanations to evolution for the next 22 years • He read about Thomas Malthus’ study which stated that the human population grows faster than the earth’s food supply—Darwin applied this idea to all of life

  30. III. Natural Selection and Evidence for Evolution • Darwin also gained insight by breeding pigeons using artificial selection • Breeders determine which individuals to use for breeding based on the natural variation • Are able to produce a wide range of plants and animals that looked very different from their ancestors

  31. III. Natural Selection and Evidence for Evolution • Darwin Explains Natural Selection • Natural selection is a mechanism that occurs when organisms with certain variations survive, reproduce and pass on their variations to the next generation • At this time, Wallace also reached similar conclusion

  32. III. Natural Selection and Evidence for Evolution • Darwin wrote a book, “On the Origin of Species” which today is still a unifying theme of biology • There is variation among population • There is an overproduction of offspring • Three is a struggle for survival, competition for food and shelter • The fittest survive and reproduce • Heritable variations are passed onto offspring • Giving way to “decent with modification”

  33. III. Natural Selection and Evidence for Evolution • Interpreting Evidence After Darwin • Modern biologists define evolution as any change in the gene pool of a population • gene pool is the combined genetic information of all the members of a population

  34. III. Natural Selection and Evidence for Evolution B. Three Types of Natural Selection • Directional Selection • Favors individuals possessing extreme values of a trait, which causes the population to move in a particular direction • If a climate becomes colder, a population may evolve in a consistent direction in response—thicker fur

  35. Directional Selection # of Individuals Phenotypic Range Shift towards ONE extreme

  36. III. Natural Selection and Evidence for Evolution • Stabilizing Selection • Acts against individuals who deviate too far from the average, favors the average • Sizes in lizards: large lizards may be subject to predation; small lizards may have a hard time defending territories, natural selection favors the average

  37. Stabilizing Selection # of Individuals Phenotypic Range Shift towards middle

  38. III. Natural Selection and Evidence for Evolution • Disruptive Selection • Adapts individuals in a population to different habitats. • Similar to directional selection—but it favors either extreme • May occur in an area that provides very different resources

  39. III. Natural Selection and Evidence for Evolution • Galapagos finches had a variety of food choices: smaller birds fed on small seeds, larger birds feed on large seeds. Natural selection favors both but not the average who would compete for both resources.

  40. Disruptive Selection # of Individuals Phenotypic Range Shift towards both extremes

  41. III. Natural Selection and Evidence for Evolution C. EVIDENCE FOR EVOLUTION

  42. III. Natural Selection and Evidence for Evolution • Fossil evidence • Not all species existed at the same time • Fossil record is fully consistent with the prediction that more “derived” groups should appear over time in the fossil record • There has not been a single case of a species out of order—no mammals mixed in the rock with early fish

  43. III. Natural Selection and Evidence for Evolution

  44. III. Natural Selection and Evidence for Evolution • Fossil evidence • Life began in the sea. The oldest fossils are marine

  45. Burgess Shale: 505 Million Year Old Coral Reef

  46. III. Natural Selection and Evidence for Evolution • Fossil Evidence • Transitions between major groups (classes) of species • Fish amphibians (transition from ray-finned fish to tetrapods (vertebrate with 4 limbs)). • Reptiles birds (Archaeopteryx) • Reptiles  mammals (synapsid reptiles (therapsids) have very mammalian characteristics

  47. The London Specimen and a reconstruction of Archaeopteryx(from Levin, 1996)