H.OriginsSu11 - Origins & Paradigms ORIGINS...

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Unformatted text preview: Origins & Paradigms ORIGINS Evidence of a Common Origin of Life on Earth • • • • Aspects Common genetic code and expression Common cell structure Common developmental patterns Common tissue & organ structure Paradigms of a for understanding the Common Origin of Life on Earth Common Origins of Life on Earth • Origin of Life • Origin of Baupläne • Paradigm: An overall framework, pattern or premise to which subsequent evidence is made to conform. • Metaphysics: of or relating to reality beyond what is perceptible to the senses. Bauplan: “Life Plan”; the underlying basic body structure and layout. • Origins of Diversity within Baupläne Metaphysical Paradigms for understanding the Origins of Life on Earth • Common Design — origin and commonality by intelligent, deliberate design (creation). • Common Ancestry — origin and inherited commonality resulting from descent from common ancestors (evolution). • Common Source — origin and commonality from import of an external stock (immigration). Heyer The many faces of EVOLUTION • Evolution: change over time. • Biological Evolution: the change in the frequency of genetic variations (alleles) in a population of organisms over time. “Descent with modification” — the theory of evolution. • The Evolutionary Paradigm: the origin and nature of the universe are products of natural forces independent of significant contributions from intelligent operations. 1 Origins & Paradigms The many faces of Charles Darwin EVOLUTION • Flunked pre-Med! F Divinity school? • Amateur naturalist for 5 years on Beagle. • Read Lyell - Earth changed gradually. - Did life change too? • Found fossils in S.Am., some who were different from their living descendants. • Microevolution: the modification and variation of components within the bauplan. • Macroevolution: the origin of novel body structures, physiological processes, or developmental patterns; major alterations of the bauplan. – “descent with modification” The voyage of HMS Beagle, 1831–1836 • Captain/Scientist Robert FitzRoy England NORTH AMERICA • Variation in tortoises, iguanas, & finches of young volcanic Galapagos. EUROPE ATLANTIC OCEAN PACIFIC OCEAN Galápagos Islands AFRICA Darwin & Galapagos HMS Beagle in port SOUTH AMERICA Andes AUSTRALIA Cape of Good Hope Cape Horn Tierra del Fuego Darwin in 1840, after his return Tasmania New Zealand Figure 22.5 Darwin’s Considerations • Upon return to England, Darwin became a recluse. (Wealthy family: so didn’t need to work.) • Gained fame by publishing accounts of the voyage. • Influenced by British elite industrial society and the philosophy of Thomas Malthus: – Society is hindered by assisting the weak. More poor are born than can survive anyway. – Society profits by favoring the successful and letting the feeble die off. Heyer Darwin’s Considerations • Had observed “descent with modification” — change over time (evolution) among species. • Fossils • Island biogeography • Knew of individual heritable variation within species. – Do some have survival-enhancing traits? • Read how artificial selective breeding could produce changes. • Sought a biological justification for Malthus’ philosophy of the “struggle for existence” and the capitalist exploitation of the poor • Resources are limited • More are born than can survive 2 Origins & Paradigms On the Origin of Species… • Alfred Russell Wallace wrote to Darwin suggesting a model of “natural selection”. To avoid being “scooped”, Darwin rushed to finish publishing his version (23 years after the voyage). • In 1858, at the same public symposium where Wallace had his paper read, Darwin released a draft of On the Origin of Species by Means of Natural Selection or The Preservation of Favoured Races in the Struggle for Life • Its two points: 1. Pattern: descent with modification 2. Process: natural selection Bumps in the road • Good theory Æ good metaphysical paradigm? • Still widespread belief in medieval concept of spontaneous generation – Rotting meatÆmaggots; old brothÆbacteria, etc. • Primitive microscopes revealed little cell structure Æ presumed to be simple • Social & technological revolution Æ intellectual elitism – Malthus, Marx, Freud, Nietzsche • Fervent publicizing by social commentators – Thomas Huxley (in England), Ernst Haeckel (in Germany) Academic interest wanes • 1865 — Gregor Mendel publishes work on genetics. Strongly critical of Darwin. • 1864 — Louis Pasteur refuted spontaneous generation • Rise of United States as technological & political power Æ democratic idealism – Variations are limited – Extrapolation of natural selection to origin of species unjustified • 1900 — Mendel’s work rediscovered Æ development of genetic theory – “All men are created equal” – Rejection of Darwinian justification for Malthus’ elite social classes – Although Darwinian influence upon social & philosophical perspectives continues, biological significance is trivialized “Neo-Darwinian” Synthetic Theory • 1937 —T. Dobzhansky, Genetics and the Origin of Species – introduced concept of mutations to evolutionary process • 1941 — Geological Society of America organizes a meeting to produce a synthetic theory of evolution reinterpreting Darwin in the context of genetic theory – Major players: • geneticists Theodosius Dobzhansky & G. Ledyard Stebbins • zoologists Ernst Mayr & Julian Huxley • paleontologists George Gaylord Simpson & Glenn L. Jepsen Popular acceptance Proposed Evidence for Evolution — Past • Biogeography • Fossil record • Homology Dobzhansky, Mayr, Huxley • 1949 —G.G. Simpson, Meaning of Evolution – joined paleontology, taxonomy, biogeography to the study of the genetics of populations. Heyer 3 Origins & Paradigms Biogeography & Convergent Evolution • Barriers to dispersal cause evolution of different biotas. • Similar habitats cause convergent evolution. • Australian mammal herbivores & carnivores are marsupials. • Animals in neo- & paleotropics have closest relatives within their respective continents. Biogeography & Convergent Evolution • Similar adaptations by unrelated taxa in similar environments NORTH AMERICA Sugar glider AUSTRALIA Flying squirrel Figure 22.17 Sedimentary Fossils Fossils & the French • Sedimentary rocks reveal fossils • Deeper, older strata have quite different organisms. • Upper strata have more familiar organisms. • Cuvier (~1800) studied Paris fossil strata – his catastrophism explained extinctions, but not origin of new forms. Pre-Darwinian early hypotheses • Naturalists extended evolving Earth to evolving life on Earth. Patterns in the Fossil Record Predictions of the paradigms • Comparative anatomists also suspected evolutionary change. • Lamarck was first to suggest fossils progressing in form. (early 1800’s) – Proposed evolution resulted from inheritance of acquired characteristics. – Rejected by observations of inheritance, but still circulated in public press. Heyer catastrophism & repeated creation or immigration initial creation & catastrophism b f fgh ab ef abcde abcdefgh younger strata i j k l older strata evolution b h a” a’ h i i’ h” ahp 4 Origins & Paradigms The predictions vs. the actual data Persistence of form Modern examples not significantly different from earliest known fossil samples • • • • • Proposed Evidence for Evolution — Past • Biogeography • Fossil record • Homology — similarities in: – Morphology (body form) – Embryology (development) – Macromolecules (proteins & DNA) horseshoe crab - 450 myo oysters - 450 myo scorpion – 320 myo shrimp – 170 myo flies & termites in amber – 25-30 myo Homologous vs. Analogous Structures • Homology : similar form presumed from divergence from a common ancestor. • Analogy : similar form presumed from convergence to a similar environment. Embryonic Homology Embryonic Homology? • 1870 - Ernst Haeckel produced a set of woodcut illustrations showing earlier stages of vertebrate embryos with greater similarities than adult forms • Embryologists complained that Haeckel had been suspiciously selective in his choice of subjects, and had exaggerated the similarities of the early stages • Never the less, these illustration were (are) widely published in popular media and textbooks • 1997 — Photographs of the real embryos reveal how distorted Haeckel’s pictures are. “It looks like it’s turning out to be one of the most famous fakes in biology.” From M.K. Richardson (1997) Anatomy & Embryology — Science 1999 • “ontogeny recapitulates phylogeny” • Darwin called it the "by far the strongest single class of facts in favor of” evolution. Heyer 5 Origins & Paradigms Embryonic Homology or Analogy? • Also, it became apparent by 1970s that the earliest stages of these embryos were very different. • Thus, any similarities at these later stages must be convergent rather than homologous! Molecular homology “Clarification of the phylogenetic relationships of the major animal phyla has been an elusive problem, with analyses based on different genes and even different analyses based on the same genes yielding a diversity of phylogenetic trees.” (Michael Lynch, "The Age and Relationships of the Major Animal Phyla," Evolution 53 (1999): 323.) Molecular vs. morphological systematics Molecular convergence?? If proteins/DNA can be related by function, they cannot be valid indicators of phylogeny! Most accepted phylogeny Echo-locating species Non-echo-locating species Presumes that all the components for echolocation evolved independently in two bat lineages, and again in toothed whales. Cladogram based on prestin gene (Analogy , not homology) Molecular (left) and morphological views of relationships among primates. Bones, molecules...or both? (20 July 2000) Nature 406: 230-233 Proposed Evidence for Evolution — Present • Breeding of plants and animals • Lab studies of captive populations • Field studies of living populations Heyer Molecular Evolution: Gene Convergence in Echolocating Mammals (2009) Current Biology 20: R62-64. Artificial Selection Appears to show dolphins more closely related to all bats than to other whales!! Origins & Paradigms NATURAL SELECTION AND ARTIFICIAL SELECTION Lab Studies: Fruit Flies • Rate of evolutionary change is related to generation time. • Fruit flies have two-week generation time. • Studies of fruit flies date to 1920’s >5,000 generations of enhanced mutations and selective breeding NATURAL SELECTION Natural Populations Evolve Today • Diseases quickly evolve antibiotic resistance. • Elephants are losing tusks - up from 3% in 1930’s to >30% today. • Darwin’s Finches evolve w/ El Nino. Drosophila melanogaster Drosophila melanogaster Evidence for Evolution Present • Breeding of plants and animals • Lab studies of captive populations • Field studies of living populations • Can observations of microevolution really be projected to conclusions about origins or even mechanisms of macroevolution??? – Modification of existing features vs. acquisition of new features or body plans. Limitations on Neodarwinian theoretical mechanisms • Mutations – Mutations are destructive alterations in previously existing complex systems Origin of the cell:The problems of irreducible complexity • Do not explain origin of the complex systems – At least in multicellular organisms, most (all?) genes have pleiotropic effects (diverse effects on multiple body functions) • Even if mutation enhances one function, it disrupts many others • Natural selection – In K-selected species, birth rate is reduced to keep population growth below carrying capacity • Avoid excess production and limit competition – In r-selected species, fecundity is so high that random success of juvenile survival overrides directional selection effects – Natural selection is more often stabilizing than is diversifying • Individuals very different from pop mean are less likely to survive or mate Heyer ÛCells ÛMost are complex. of the components, processes, and pathways need to be already present and functioning for any one component to work. Origins & Paradigms A problem of origins: which came first? What does a cell need? • Selective isolation from environment (plasma membrane) • Energy (ATP) • Instructions (DNA) • Machinery to carry out instructions and regulate processes (proteins) • Compartmentalization of incompatible or specialized activities in time or space (organelles) Emergent Systems The problems of irreducible complexity: • Emergent Systems Analysis: mapping all interactions within the holistic living complex. • Life processes are not only complicated, they’re interdependent! molecular machines Fig. 1.10 CELL Nucleus Cytoplasm Outer membrane and cell surface A systems map of known interactions among 3500 proteins in a fly cell Stereo Isomers (Enantiomers) — mirror-image macromolecules One of the great mysteries of the origin of living cells — Three Questions / Three Models • Extrapolations of microevolution to macroevolution not as solid. Alternative mechanisms? • All non-biological synthesis reactions of organic molecules produce both D- and L- isomers in equal yield. Design • And all non-biological reactions using organic molecules as reactants react with both D- and L- isomers equally. Origin of • Yet, living cells are constructed only of D-sugars and L-amino acids! Origin of Life Baupläne • \ not a product of natural reactions? Evolution Immigration ? ? ? Macroevolution •Homology x • Fossil record • Artificial selection Origin of L-Dopa Heyer D-Dopa (biologically active) (biologically inactive) Microevolution Diversity •Biogeography •Fossil record •Artificial selection •Field observation ...
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