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Evolution

Evolution. The Nature of Change and Variation . What is Evolution?. Simply… a change in living organisms over time. Why study evolution?. Evolutionary concepts provide a solid foundation to much of modern biology

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Evolution

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  1. Evolution The Nature of Change and Variation

  2. What is Evolution? • Simply… a change in living organisms over time

  3. Why study evolution? • Evolutionary concepts provide a solid foundation to much of modern biology - you can’t fully understand current trends in biology or you will have difficulty understanding evolution

  4. Why Study Evolution? • Evolution • involves inheritable changes in organisms through time • is fundamental to biology and paleontology • Paleontology is the study of life history as revealed by fossils • Evolution is a unifying theory • like plate tectonic theory • that explains an otherwise encyclopedic collection of facts • Evolution provides a framework • for discussion of life history

  5. Misconceptions about Evolution • Many people have a poor understanding • of the theory of evolution • they hold a number of misconceptions, • which include: • evolution proceeds or advances strictly by chance • nothing less than fully developed structures • such as eyes are of any use • there are no transitional fossils • so-called missing links • connecting ancestors and descendants • humans evolved from monkeys • so monkeys should no longer exist

  6. What is a scientific “theory”? Evolutionary theory is the framework tying together all of biology. It explains similarities and differences between organisms, fossils, biogeography, drug resistance, relative virulence of parasites, and much more. Theories are structures of ideas that explain and interpret facts. 

  7. In the early days... • Prior to 1760 -people believed organisms were fixed- that is they didn’t change • 1744-1829 – Jean Baptiste Lamarck • Evolution through the inheritance of acquired characteristics • Traits acquired during an organism’s life could be passed on to their offspring • Giraffes long necks explained by repeated stretching • hypothesis rejected

  8. Lamarck’s Giraffes • ancestral short-necked giraffes • stretched their necks • to reach leaves high on trees. • Their offspring were born • with longer necks • According to Lamarck’s theory of inheritance of acquired characteristics

  9. Lamarck’s Theory • Lamark’s theory was not totally disproved • until decades later • with the discovery that genes cannot be altered by any effort by an organism during its lifetime

  10. Basic Types of Evolution • Macroevolution = speciation – the formation of new species. The change in species over long periods of time. Not immediately observable. • Microevolution= changes in genes/alleles within a population. • Can be observed in a human lifetime.

  11. Macroevolution 1. Large-scale changes in gene frequencies 2. Occurs over a longer(geological) time period 3. Occurs at or above the level of speciesin separated gene pools 4. Consists of extended microevolution Microevolution 1. Small-scale changes in gene frequencies 2. Occurs over a few generations 3. Occurs within a speciesor population in same gene pool 4. Refers to smaller evolutionarychanges Macroevolution/Microevolution

  12. Macroevolution 5. Has not been directly observed 6. Evidence based on remnantsof thepast 7. More controversial 8. Example: Birds from reptiles Microevolution 5. Observable 6. Evidence produced by experimentation 7.Less controversial 8. Example: Bacterial resistance to antibiotics Macroevolution/Microevolution

  13. Biological Evidence Supporting Evolution • If all existing organisms descended with modification from ancestors that lived during the past, • all life forms should have fundamental similarities: • all living things consist mainly of carbon, nitrogen hydrogen and oxygen • their chromosomes consist of DNA • all cells synthesize proteins • in essentially the same way

  14. Evolutionary Relationships • Biochemistry provides evidence for evolutionary relationships • Blood proteins are similar among all mammals • Humans’ blood chemistry is related • most closely to the great apes • then to Old World monkeys • then New World monkeys • then lower primates such as lemurs • Biochemical test support the idea • that birds descended from reptiles • a conclusion supported by evidence in the fossil record

  15. Natural Selection—Main Points • Organisms in all populations • possess heritable variations such as • size, speed, agility, visual acuity, • digestive enzymes, color, and so forth • Some variations are more favorable than others • some have a competitive edge • in acquiring resources and/or avoiding predators • Not all young survive to reproductive maturity • Those with favorable variations • are more likely to survive • and pass on their favorable variations

  16. “Survival of the Fittest” • In common nonscientific usage, • natural selection is sometimes expressed as • “survival of the fittest” • This is misleading because natural selection is not simply a matter of survival • - but involves differential rates • of survival and reproduction

  17. Not only Biggest, Strongest, Fastest • One misconception about natural selection is that among animals • only the biggest, strongest, and fastest • are likely to survive • These characteristics might provide an advantage • but natural selection may favor • the smallest if resources are limited • the most easily concealed • those that adapt most readily to a new food source • those having the ability to detoxify some substance • and so on...

  18. Darwin observed Galapagos finches showing variations in beak shape and size from island to island. He reasoned these differences made the finches better adapted to the food in their particular local environment. Each finch population had developed beaks which were suitable for that particular environment.

  19. Phylogenic Tree Phylogenic trees trace patterns of shared ancestry between lineages. Each lineage has a part of its history that is unique to it alone and parts that are shared with other lineages.

  20. Limits of Natural Selection • Natural selection works • on existing variation in a population • It could not account for the origin of variations • Critics reasoned that should a variant trait arise, • it would blend with other traits and would be lost • The answer to these criticisms • existed even then in the work of Gregor Mendel, • but remained obscure until 1900

  21. Evidence of Change • Fossil Record • Embryology • Molecular Biology-Amino Acids, Nucleotides, DNA sequencing, mitochondrial DNA • Anatomy commonalities • Various adaptations

  22. EVIDENCE OF EVOLUTION • STRUCTURAL ADAPTATIONS • MIMICRY • CAMOUFLAGE http://evolution.berkeley.edu/evolibrary/home.php http://science.howstuffworks.com/animal-camouflage2.htm

  23. Fossil Record • Fossils are a major source of information about changes in life during the distant past • In general, fossils show that life has increased in diversity and complexity over time

  24. Fossil Record • Interpretation of the distribution of fossils in the rock initially based on the principle of superposition - in undisturbed rock layers, older fossils will be found lower in the rock than younger fossils -radiometric dating confirms this • In general older life forms tend to be less complex • Periods of diversity are interrupted by mass extinctions – followed by new life forms • Fossil Record is incomplete – estimated only 1 in 10,000 extinct species are represented – Why?

  25. Embryology • All vertebrate embryos have • Gill slits on sides of the throat • Post anal tail • The fact that organisms without gills, or tails have them as embryos is taken as evidence of a common ancestry with organisms that had both • Which is the fish, rabbit, human, chicken, tortoise?

  26. Comparative Anatomy • Similarities in structure between organisms was used to determine evolutionary relationships

  27. Other Proof From Anatomy • Vestigial structures – structures that are greatly reduced with little or no function - they are thought to be left over from ancestors • Pelvis and leg bones in snakes • Reduced toe in horse • Appendix in human • Coccyx (tail bone) in humans

  28. Vestigial Structures

  29. Comparative Anatomy • Analogous Structures • Similar function but different structure - • Insect’s wing, Bird’s wing and Bats wings – all allow flight, but are structurally different • Eyes of Mollusks and Vertebrates – both allow sight, but are different in structure

  30. Comparative Anatomy • Homologous Structures • Have a similar structure but different function • The forelimbs of vertebrate animals all have the same structural design, but they have different functions • This similarity of structure shows a common ancestry

  31. Homologous Structures Analogous structures

  32. Molecular Biology Comparisons of the sequences of amino acids in proteins or nucleotides in DNA can show the relationships between organisms the number of differences in the sequences of amino acids or nucleotides indicates how closely related two organisms are

  33. Hemoglobin Comparison Species AA differences from humans Gorilla 1 Rhesus Monkey 8 Mouse 27 Chicken 45 Frog 67

  34. Hemoglobin Cladogram

  35. Cladogram (family tree) created from a fossil record

  36. Bird Evolutionary Tree Phylogenic Trees and Cladogramsare also created using comparative DNA sequences. If the DNA is very similar to each other, it means they share a fairly recent common ancestor.

  37. Darwin Developed the Theory During his voyage, Darwin observed fossil mammals in South America that are similar to yet different from present day animals. Ex. Llamas, sloths, and armadillos. The finches and giant tortoises lining on the Galapagos Islands vary from South America, even though they differ in subtle ways. These observations convinced Darwin that organisms descended with modification from ancestors that lived during the past which was his central claim of the theory of evolution.

  38. Charles DarwinAlfred Wallace • Descent with modification. • The Origin of Species. 1859 • Species were not created in their present forms but evolved from an ancestral species. • Natural selection, the mechanism by which change occurs (Explanation of how evolution occurs).

  39. Darwin and Wallace • Darwin and Alfred Russel Wallace (1823-1913) • read John Malthus’ book • and came to the same conclusion, • that a natural process • was selecting only a few individuals for survival • Darwin’s and Wallace’s idea • called natural selection • was presented simultaneously in 1859

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