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L.Origins08 - Origins ORIGINS Evidence of a Common Origin...

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Unformatted text preview: Origins 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 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/intelligent design). • 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 • 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. 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 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 Gal ápagos 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 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 The Races in the Struggle for Life • Its two points: 1. Pattern: descent with modification 2. Process: natural selection Fitness and Selection Terms used in Natural Selection • Fitness: measure of how many genes you pass on to future generations. • Differential representation of genes in future generations due to differential survival to reproductive maturity. – Requires heritable (genetic) variation among individuals. • If differential survival is based upon expressed genotypic differences – it may lead to changes in population gene frequency. Modes of Selection • Darwinian fitness is a relative measure – how many offspring does one individual leave relative to others in the population. • Inheritance acts upon genotype • Selection acts upon phenotype – morphology, physiology, or behavior • Agents of selection – physical environment – biological environment • Factors within species or between species Popular acceptance of the Darwinian premise • 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 Bumps in the road • 1864 — Louis Pasteur refuted spontaneous generation • Rise of United States as technological & political power Æ democratic idealism – “All men are created equal” – Rejection of Darwinian justification for Malthus’ elite social classes • Fervent publicizing by social commentators – Thomas Huxley (in England), Ernst Haeckel (in Germany) Heyer 3 Origins Academic interest wanes “Neo-Darwinian” Synthetic Theory • 1865 — Gregor Mendel publishes work on genetics. — Strongly critical of Darwin. • 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 Mendelian genetic theory – Variations are limited – Extrapolation of natural selection to origin of species unjustified • 1900 — Mendel’s work rediscovered Æ development of genetic theory – Although Darwinian influence upon social & philosophical perspectives continues, biological significance is trivialized Proposed Evidence for Evolution — Past – Major players: • geneticists Theodosius Dobzhansky & G. Ledyard Stebbins • zoologists Ernst Mayr & Julian Huxley • paleontologists George Gaylord Simpson & Glenn L. Jepsen Dobzhansky , Mayr , Huxley 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 • Fossil record • Homology Biogeography & Convergent Evolution Sedimentary Fossils • Similar adaptations by unrelated taxa in similar environments • Sedimentary rocks reveal fossils NORTH AMERICA Sugar glider AUSTRALIA Figure 22.17 Heyer Flying squirrel 4 Origins Fossils & the French • 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. Patterns in the Fossil Record Predictions of the paradigms catastrophism & repeated creation or immigration initial creation & catastrophism b f fgh ab ef abcd abcdefgh younger strata i j k l older strata The predictions vs. the actual data evolution bc g h’ a” a’ h i i’ h” ahp Persistence of form — evolution is not inevitable 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) Heyer 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. 5 Origins 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. Embryonic Homology or Analogy? Molecular homology • 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! BUT — The pattern is not consistent with the pattern from comparative anatomy. Proposed Evidence for Evolution — Present Artificial Selection • Breeding of plants and animals • Lab studies of captive populations • Field studies of living populations Heyer 6 Origins NATURAL SELECTION AND ARTIFICIAL SELECTION But — Is there a limit to variation? Lab Studies: Fruit Flies • Rate of evolutionary change is related to generation time. • Studies of fruit flies date to 1920s • Fruit flies have two-week generation time. >5,000 generations of enhanced mutations and selective breeding NATURAL SELECTION Field Studies of Natural Populations • Diseases quickly evolve antibiotic resistance. • Elephants are losing tusks - up from 3% in – up from 3% in 1930s to >30% today. Drosophila melanogaster Drosophila melanogaster Directional Selection: Peppered Moth, Biston betularia • Darwin’s Finches evolve w/ El Nino. Industrial melanism in early 1900’s 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??? Limitations on Neodarwinian theoretical mechanisms • Mutations – Mutations are destructive alterations in previously existing complex systems • Do not explain origin of the complex systems – 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 species that limit their populations, birth rate is reduced to keep population growth below carrying capacity • Not more born than can be supported – In species that do not limit their populations, reproductive rate is so high that random success of juvenile survival overrides selection – Natural selection is more often stabilizing than is diversifying • Individuals very different from average are less likely to survive or mate Heyer 7 Origins Origin of the cell:The problems of irreducible complexity ÛCells are complex. ÛMost of the components, processes, and pathways need to be already present and functioning for any one component to work. 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 (organelles) Emergent Systems • Emergent Systems Analysis: mapping all interactions within the holistic living complex. • Life processes are not only complicated, they ’re interdependent! Fig. 1.10 CELL Nucleus Cytoplasm Outer membrane and cell surface A systems map of known interactions among 3500 proteins in a fly cell The problems of irreducible complexity: molecular machines Stereo Isomers (Enantiomers) — mirror-image macromolecules One o f t he g reat m ysteries o f t he o rigin o f l iving c ells — • All non-biological synthesis reactions of organic molecules produce both D- and L- isomers in equal yield. • And all non-biological reactions using organic molecules as reactants react with both D- and L- isomers equally. • Yet, living cells are constructed only of D-sugars and L-amino acids! • \ not a product of natural reactions? L- Dopa Heyer D-Dopa (biologically active) (biologically inactive) 8 Three Questions / Three Models • One paradigm fits all? Or different answer to each question? Design Origin of Life ? Evolution ? Three Questions / Three Models • The Theory of Evolution = microevolution – Important central concept of biology & ecology Design ? Origin of Life Origin of Origin of Baupl äne Origin of Diversity ? ? ? ? ? ? Three Questions / Three Models • Extrapolations of microevolution to macroevolution not as solid. Alternative mechanisms? Design Origin of Life Origin of Baupl äne ? • Fossil record • Artificial selection Evolution Baupl äne ? Macroevolution •Homology Microevolution Diversity •Biogeography •Fossil record •Artificial selection •Field observation ? ? ? ? ? Diversity Microevolution •Biogeography/convergence •Fossil record •Artificial selection •Field observations Three Questions / Three Models • About equal proponents of each paradigm. Design Origin of x Origin of Immigration Origin of Immigration ? Evolution ? Immigration Life Origin of Baupl äne Origin of Diversity • Irreducible complexity • Anabolic kinetics • Selected isomers • Molecular machines ? Evolution Immigration ? • Hydrocarbons in stellar clouds • Amino acids in meteor rocks ? x ¸ 9 ...
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