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EVOLUTION W 17

evolution • nothing in biology makes sense except in the light of evolution physics and chemistry: whole from components biology: whole from components in light of evolutionhypothesis • cannot prove, only gather supporting evidence, use observations to explain mechanism

Linnaeus • 1707-1778• binomial ‘2 name’ species naming system • first recorded concept of species change over time• humans from different continents are different species, used phenotype, did not look at teeth,

Biological species concept would argue humans as separate speciesLamarck • 1744-1829 Lamarckian evolution - discards concept of fixed species

• First Law: use or disuse of structures causes enlargement or shrinkage • Second Law: changes are heritable, continuous

Influences on Darwin: Lyell • geologist, earth changes gradually ‘Principles of Geology’ Malthus • human population size limited by resources ‘Essay on the Principle of Population’Evolutionary thought before and after Darwin, combats complete, divine life.Darwin’s Personal Life• married first cousin with riches• medical school• clergyman training• met Prof. Henslow (botanist) and Prof. Sedgwick (geologist)

Henslow nominates Darwin to be naturalist and conversationalist for Captain Fitzroy Beagle • 1831-1836

• notices variation in a population of the same species• mocking thrushes and Galapagos tortoises morphologically different between islands,

mainland South American tortoises all similar0looking• Galapagos finches, speciation from mainland, subspecies, first phylogeny?

Wallace and Darwin independently formulated idea of natural selection.Darwin’s Evolution by Natural Selection: APPLY NEO-DARWINIAN THEORY OF EVOLUTION • MODERN SYNTHESIS

• individuals within species variable VARIATION IN ALLELE FREQUENCIES LEADING TO PHENOTYPIC VARIATION (SOME GENETIC VARIATION DOES NOT IMPACT PHENOTYPE)

• phenotypic variation inheritable by offspring NOT CULTURAL, HERITABLE• more offspring produced than survive (AND REPRODUCE)• survival and reproduction non-random (PHENOTYPE MODIFIED BY ALLELES INCREASES FITNESS)

Darwin’s Theory: • non-constancy of species• descent of all organisms from common ancestors (branching)• gradualness of evolution• multiplication of species (origin of biodiversity)• decent with modification, environmental change � evolution

homologous trait • inheritance from a common ancestor synapomorphies • shared derived characters ⇢ whales descendants of terrestrial mammals, hippos mammary glands, 3 middle ear bones, hair in developing embryos ⇢ fish from convergent evolution • body form similar, evolved independently ⇢ changes in gene expression led to hindlimb loss in dolphins

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Darwin publishes ‘Origin of Species’ in 1859, Issues: • blending inheritance/pangenesis • inheritance elements act like pigment in paint• did not resolve relationship between natural selection and Lamarckian use/disuse• initial effects of natural selection (white fur) nullified by crossing black fur - did not understand

genetics

The Great Debate, 1860: Huxley (pro-evolution) debates Archbishop WilberforceMendel, 1865 (ignored until 1900) • dominant and recessive traits (possible to ‘recover’ traits)

The Modern Synthesis: 4 major empirical Neo-Darwinists 1. Dobhanksy ‘Genetics and the Origin of Species’, 1937 - mendelian genetics + Darwin’s theory of

natural selection, recognized mutations - small effects on phenotype most important, recognized genetic drift

2. Mayr ‘Systematics and the Origin of Species’, 1942 - Biological Species Concept, Allopatric (geographical) separation (who lives and reproduces based on whole phenotype, not genetics (but phenotype is genetically-based)

3. Simpson ‘Tempo and Mode in Evolution’, 1944 - fossil horses, linear fossil sequence with toe reduction but opposed continental drift, Wegener, despite fossil evidence in North American and Asia

4. Stebbins ‘Variation and Evolution in Plants’, 1950 - instant speciation: allopolyploids (from 2 species), autopolyploids (doubling within a species)

Modern Synthesis: 1937-1947, Evolution by Natural Selection, 1986 reference1. populations contain genetic variations that arise by random mutations and recombination2. populations evolve by changes in gene frequency as a result of random drift, gene flow, and

natural selection3. most adaptive genetic variants will have slight phenotypic effects individually, brining about

gradual phenotypic change4. diversification from speciation, gradual evolution of reproductive isolation among geographically

isolated populations (but only believed with isolation! wrong)5. speciation gives rise to changes of great magnitude, warranting the designation of taxonomic

levels

Biological Evolution • change in heritable traits in a population that occurs between generations because of one or more of the following:

1. Natural Selection - higher survival and/or reproduction of individuals that differ in measurable traits

2. Genetic Drift - random variation in allele frequencies at a locus cause by gamete sampling error3. New mutation of recombination - in a genomic DNA sequence4. Immigration - from genetically divergent populations that successfully reproduces

Palaeontology • biases in hard parts, classes, environment - marine animals living in mid more likely to be preserved, tar, etc.

Fossils - only in sedimentary rock, eg. limestone, sandstone, shale• impression• perimineralized ⇢ date with radioactive decay• casts and moulds• exceptional preservation (soft parts, rare; Lagerstätten)

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Evolution:

Hypothesis I, Punctuated Evolution • ‘jumps’ in lineages of fossils (punctuation) because large change sin morphology,

evolution happened quickly compared to geological timeHypothesis II, Gradual Evolution • ‘jumps’ in lineages of fossils gradual, but artifact of preservation, sediment did not

preserve all stages

Earth dated as 4.6 by old largely using rubidium - rubidium-87 amount indicative of time spent in radioactive decay, 4 by old rocks in Great Slave Lake, Canada

First unicellular life (cyanobacteria) fossilized 3.45 Bya, oldest rocks dated 4 Byabut biochemical signs of 3.7 by old archaea

How did life come to Earth so quickly? Hypothesis I, Extraterrestrial origin of life theory • organic molecule formation in space: cosmic dust + UV = chemicals• arrived to Earth via asteroids, Murchison Meteorite * amino acids are right-handed, humans only

posses left-handed, different chirality than investigatorsEarliest bacteria fossils, stromatolites of cyanobacteria

• stromatolites - layers of bacteria and silt, colonies, mats of filamentous cyanobacteria• blue-green algae evidence by chlorophyll A and accessory pigments, fossil evidence of

stromatolite 3.4 Bya in Australian DesertLiving and fossilized cyanobacteria look ‘identical’, bacteria makes up most of Earth’s biodiversity and biomass

Earliest archaea fossils • 3.5 by oldEarliest eukarya fossils • 1.8 Bya - transition from unicellular to multicellular life may have occurred multiple times, independently

fossils ⇢ eukaryotic, multicellular photoautotrophs, microalgae (green seaweed) 16. Bya red algae (bangiomorpha) 1.2 Byafossils ⇢ eukaryotic, multicellular animals, small sponge 600 Mya at time of snowball Earthfossils ⇢ eukaryotic, multicellular fungi, mushroom 113 Mya (closer to humans than plants)

but first eukaryotic, multicellular embryos 580 Mya China controversy:protostome cleavage pattern, thought snowball Earth was tool cold, bacteria? rocks?

Ediacaran, 580 Mya, multicellular animals • ‘failed experiment in life’, evolved,

diversified, extinct within 40 my• only a fraction of Ediacaran animal fauna

share traits with extant animals

Cambrian, 505 Mya, multicellular animals • more mobility, more consumers (predators),

life below sediment• most existing animal lineages found in

Cambrian fossil record including chordates, extant and unique lineages recognizable

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