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  1. SPU-22: The Unity of Science from the Big Bang to the Brontosaurus and Beyond Lecture 18 9 April 2014 Science Center Lecture Hall A

  2. Outline of Today’s LectureStart Of Part III: Story Of Life General Introduction Darwin and Wallace on evolution, created tsunamis still being felt in many parts of world Given time, Mendel and Miescher’s critical contributions

  3. Semi Historical Approach Bewildering forms of life everywhere Size scale spreads over c. 8 powers of 10 No tools or background to seek answers to fundamental questions Concentrated first on classification (we’ll pick up detailed story in mid 1800s)

  4. Research Style In Biology In contrast to establishment of paradigm of plate tectonics, which required scores of scientists working collaboratively, research in biology that led to present model of evolution was mostly singular affair: single persons working alone, albeit quite aware of discoveries made before, reached goal

  5. Pertinent Preface Story of search for fundamental understanding of biological world has too many threads, requiring somewhat subjective selection Path I chose is reasonably clear and reasonably accurate -- my hope at least Nonetheless goal of avoidance of jargon will be somewhat violated, albeit with provision of explanations

  6. Fossils and Evolution Fossil finds showed that creatures were extinguished throughout “history” Species exist now that did not always exist (note, however, that absence of evidence is not always evidence of absence)

  7. Evolution And Missing Motor Who could possibly have doubted that some sort of evolution had taken place in earth’s history? [Next funny question!] As in continental drift, however, motor was missing

  8. Darwin’s Contribution: Background Trained in geology; well-to-do family Agreed to go on 5-year voyage on Beagle Acute observer of life forms of all sorts; thought deeply about observations Content of field at time: observers and thinkers. Darwin was both

  9. Some Of Darwin’s Views From Voyage Of Beagle 1. Fauna of different South American climate zones were related to each other rather more than to fauna from same climate zones elsewhere (i.e., on different continents) • Fauna of nearby islands related to those of nearest mainland; related species are present on different islands of archipelago • Began to form views on evolution

  10. Darwin’s Conclusions From These Observations These facts, gathered from voyage of Beagle, were inconsistent with creationist explanation, but were entirely consistent with evolutionary interpretation. Decided on (macroscopic) motor: Natural Selection From these and other facts that he gathered, Darwin argued strongly against evolution by major steps (“saltation”) and in favor of small changes, virtually imperceptible from one generation to next. He also used arguments based on fauna domestication

  11. Linnean Society Published in 1858 letters and essays received from Darwin and Wallace. (Interesting story leading up to this result.) “We feel it desirable … that views founded on a wide deduction from the facts … should together be laid before the public.” Lyell, Hooker, and Bennett

  12. Charles Darwin (1809-1882)

  13. Charles Darwin (1809-1882)

  14. Alfred Russell Wallace (1823-1913)

  15. Alfred Russell Wallace (1823-1913)

  16. Darwin And Wallace Relations Were very respectful of each other Wallace deliberately stayed in background Darwin helped Wallace get pension Had “falling out” over Wallace’s backtrack for human mind…Now back to science

  17. Question Of Balance Both Darwin and Wallace were familiar with Malthus: inexorability of exponential growth unless checked. [Easy to show how reproduction of any species could be expected to soon overwhelm earth unless checked.] There were many means in nature to provide such checks; Darwin and Wallace each discussed representative number in detail. Basis for natural selection

  18. Darwin And Struggle For Existence “ The struggle almost invariably will be most severe between the individuals of the same species, for they frequent the same districts, require the same food, and are exposed to the same dangers.”

  19. Darwin on Natural Selection “On the view that each species has been independently created, I can see no explanation of this great fact (sic) in the classification of all organic beings; but, to the best of my judgment, it is explained through inheritance and the complex action of natural selection, entailing extinction and divergence of character.”

  20. Heart Of Natural Selection Darwin noted extreme variability of individuals of any species. What, he wondered, did Nature do with all of this variability? Genetic information passed from one generation to next is not all random, but it is statistically predictable property of genetic material, whatever it might be. Natural selection -- -- “survival of the fittest” -- -- is direction-giving force. The previously missing motor!

  21. Heart Of Natural Selection (Cont’d) Darwin fleshed out idea of natural selection for wide variety of species and environmental circumstances, as did Wallace in his independent work Nonetheless, it is true that Darwin was vague and somewhat confused about the origin of genetic variation, now known to every school child who has taken first course in biology. These insights, however, only came much later, and were hard-won, as we shall see

  22. Other Attributes Of Natural Selection Statistical survival depends not on accident, but on genetic gifts In every population, only some organisms reproduce; number varies with species and circumstances Success in having progeny is key; mere survival is useless in propagating species. The motor of natural selection also, willy nilly, solved age-old problem of teleology, an approach that goes back apparently at least as far as Aristotle

  23. Origin Of Species: The Book Darwin entitled it “Abstract,” meaning its 500 pages were precursor to full-length treatment! His publisher nixed this idea Book, by and large, gives no credit to precursors, and has no references, and so states: no time Rushed into print because Darwin knew of Wallace’s work and wanted to protect his priority, which overcame his desire to first develop book to much greater length (despite very good personal relations with Wallace) As you all know, the controversy created by this book, and by later “Descent of Man,” continues strong today

  24. Darwin’s Final Words In Origin of Species “There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”

  25. Reaction To Origin Of Species In 1859, Darwin’s book hit like hydrogen bomb. Apparently elite were vociferous in their objections; laypeople apparently took little notice. “Outstanding” naturalists had been opposing evolution for preceding three decades. Compare with today.

  26. Why Fuss Now? Predecessors who had been pushing evolution did not create much of stir. Why? 1. Their words/ideas were clearly only vague speculations 2. They were generally uninformed, unaware, and uncritical about complications 3. They inserted their arguments in treatises dedicated primarily to other subjects

  27. Why Fuss Now? (Cont’d) By contrast, Origin was massive (~500 page), well organized, well buttressed account, based on data collected over large fraction of world and thorough examination of existing literature, as well as containing results from correspondence with many of world’s experts -- all distilled into one book, rivaling Bible in length, if somewhat different in content Darwin took great pains to think of all possible objections to his arguments and to provide answers as cogently as he could. [Evidence? His autobiography.]

  28. Why Fuss Now? (Concluded) For all of these reasons, Darwin was taken seriously Interestingly, Darwin had no intention of challenging religion. Indeed, he was apparently very careful in his wording not to offend

  29. Big Question: What Is A Species? Answer: It depends on one’s definition, which was at least until recently source of some controversy. Nature, in form of biology, is incredibly complicated; finding definition useful over entire range of organisms, especially of extinct organisms, may well be chimerical pursuit P.S. Opponents of evolution often note that, for example, breeding of dogs always beget dogs – never different species

  30. Fleeming Jenkin’s Objections There is no evidence for changes in species There is a limit to the extent of change (e.g., horses can be bred to run only so fast) Future breeding of “outliers” tend to show a reversion to the (prior) mean: see next slide These objections were based on tacit understanding of heredity as continuous (e.g., mixing) process; the correct process, discrete one, was unknown to anyone in that era

  31. Criticism Of Evolution Via Natural Selection Criticism of Origin of Species, exemplified by exhaustively argued review of later edition by Fleeming Jenkin, e.g.: “How could natural selection possibly work given the (then) well-known tendencies of inherited characteristics in successive generations to migrate to the (prior) mean (and with limits as to how far that characteristic could stray from the mean)?”

  32. Response To Criticism Problem: Darwin did not have correct model, in fact only hazy model, of heredity. Even Huxley did not have satisfactory answer to above critique

  33. Other Comments Darwin and Wallace were first evolutionists not to seek refuge in extra-observational bases (e.g., God did it – except for Wallace’s later retreat). Natural selection was simplicity itself Thomas Huxley reacted with: “How extremely stupid of me not to have thought of that.” Other critics noted: “Darwin proposed a mechanical, soulless, universe.”

  34. Gregor Mendel’s New Approach To Biology All advances in biology, through time of Darwin, were based on observations and thought Mendel introduced experiments into biology – major advance He hunted for law(s) governing heredity

  35. Mendel And Experimental Biology Everyone has heard of Gregor Mendel and his new approach: experiments with peas; how many have read his original paper (even in English translation)? Description of his experiments (why undertaken?) Disappearance of results from view Resurrection and relentless(?) criticism

  36. Mendel’s Warning Many historians viewed Mendel as “lucky” to have discovered laws of heredity Background as teacher may explain his well-organized presentation Near end of paper, he noted - foreshadowing for this course - different characteristics were not so simply treated and indeed he had no idea how to treat them

  37. Experiments In Plant Hybridization (1857 - 1865) Selection of plant key to useful study: 1. Possess clear differentiating characteristics 2. Hybrid must be protected during reproduction from “foreign” influences 3. Hybrids must show no strong change in fertility in successive generations

  38. Mendel’s Pea Plants Bred sets of pea plants to be reliable carriers of one of two distinctive characteristics, e.g., smooth seeds or wrinkled seeds; long (6 to 7 feet) stems or short (1 to 1.5 feet) stems Bred large number of plants with one characteristic with large number of plants with the other characteristic, one on one, producing many offspring

  39. Experimental Details Experiments involved 10,000 plants Description of details covered ca. 15 pages, but leave many possibly important issues untreated or treated only in part Analysis assumed ab initio that “mothers and fathers” contribute equally to inheritance

  40. Mendel’s Results All of first-generation offspring exhibited one and only one of two possible characteristics of any trait (e.g., all long stems and smooth seeds). That is, one of each pair of traits proved dominant and other, by definition, recessive When only these offspring were bred among themselves, next generation showed clear difference: About three-quarters of plants exhibited dominant trait and one quarter corresponding recessive trait

  41. Experiments in Plant Hybridization: The Paper Clearly written (marred somewhat in its English translation by misprints) Credit is properly given to his predecessors, but without including critiques he doubtless had Major advance over his predecessors: Instead of studying many different plant generations of many different plants in a helter-skelter manner, Mendel did one series of well planned, careful, connected experiments, extending over eight years. He thereby discovered simple law missed by all predecessors

  42. Effect on Scientific Community Results presented at scientific meeting and subsequently published; then disappeared like stone in ocean Blame placed by many historians on von Nageli

  43. von Nageli’s Great Work On Theory of Organic Evolution Simon Mawer’s comment: “We can forgive von Nageli for being obtuse and supercilious. We can forgive him for being ignorant, a scientist of his time who did not really have the equipment to understand the significance of what Mendel had done despite the fact that he (von Nageli) speculated extensively about inheritance. But omitting an account [or even mention] of Mendel’s work from his book is, perhaps, unforgivable.”

  44. Resurrection Mendel’s work was rediscovered independently and almost simultaneously by three scientists from three countries Soon after, injustice done to Mendel was picked up by William Bateson who wrote a widely distributed book in 1909 on Mendel’s work, thus leading to Mendel’s penetrating, and remaining in, consciousness of scientists and of all students of genetics, including those at high school level. Bateson’s colleague, Reginald Punnett, invented Punnett squares (PR had amazing effects even then)

  45. Example Of Punnett Square

  46. Criticism Statisticians have thrusted and parried over Mendel’s results for about century Nub of issue, as almost always in these matters, relates to critics’ assumptions and their bases Charge was that Mendel’s results were closer to his expectations than probability theory indicated was at all reasonable

  47. Criticism (Concluded) Details are arcane No one, however, ever accused Mendel of fraud; quite contrary Possible explanations include: unconscious bias (placement of doubtful plants on “side” favoring his hypothesis; discarding of data thought to be contaminated) his assistant did it

  48. Gregor Mendel (1822-1884)