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Transcript
Big questions in evolution Evolution is the phenomenon of modification with descent • Why do species change? • How do new species arise? (it is not natural selection) Hawaiian Drosophila • A (very brief) history of evolutionary thought • Hyracotherium (50MY) Why do species go extinct? Darwin and the Beagle: 1831-36 Aristotle and Plato – Archetypes (i.e. no evolution, variation is meaningless) • Buffon, Cuvier, Smith – Importance of fossils. Earth may be old. • Hutton, Lyell – Current geological processes can explain earth, but only on a long time-scale • Lamarck and Erasmus Darwin – Transmutationism – Inheritance of acquired characeteristics or ‘use and disuse’ – Universal common ancestor <<insert picture p432 Campbell>> Equus What Darwin said Darwin’s finches Geospiza Organisms produce too many offspring Heritable differences exist in traits influencing the adaptation of an organism to its environment Organisms that are better adapted have a higher chance of survival Also Alfred Russell Wallace – letters to Darwin prompted publication of ‘On the Origin of Species’ The Huxley – Wilberforce debate Arguments against Darwin • Biblical – Earth is only about 4000 years old • Tautological – Which are the fitter organisms? Those which survive. • Paley’s blind watchmaker – How can complex structures arise by a ‘blind’ process? I asserted - and I repeat - that a man has no reason to be ashamed of having an ape for his grandfather. If there were an ancestor whom I should feel shame in recalling it would rather be a man-a man of restless and versatile intellect-who, not content with an equivocal success in his own sphere of activity, plunges into scientific questions with which he has no real acquaintance, only to obscure them by an aimless rhetoric, and distract the attention of his hearers from the real point at issue by eloquent digressions and skilled appeals to religious prejudice. • The problem of heredity – How can natural selection work? Gradualist steps in the origin of the molluscan eye What is the evidence for evolution? • • • • The fossil record – Origin of diversity – Continuity of form – Simultaneous shifts in climate and fossil fauna Darwin and heredity • Darwin viewed heredity as a blending process • BUT blending inheritance removes variation which is essential for natural selection • Francis Galton’s law of heredity attempted to provide a mathematical basis for Darwin’s views (later reinterpreted by Karl Pearson) • Major controversy in the early 1900s arose between those who supported Darwin’s view and those (led by Galton) who rejected them The fossil record – different forms of life Ediacara Burgess Shale Direct observation – Industrial melanism – Drug resistance – Experimental Species complexes – Hybrid zones – Ring species Dickensonia ~ 550 MY Marella ~ 500 MY Homology – Similarity through common descent – From anatomy to molecular biology Burgess shale Fossils – continuity of form How are fossils formed? Homo erectus 1.8 MY • unaltered preservation • permineralization=petrification – like insects or plant parts trapped in amber, a hardened form of tree sap Homo sapiens (early form) 0.18 MY – in which rock-like minerals seep in slowly and replace the original organic tissues with silica, calcite or pyrite, forming a rock-like fossil - can preserve hard and soft parts - most bone and wood fossils are permineralized • replacement – An organism's hard parts dissolve and are replaced by other minerals, like calcite, silica, pyrite, or iron • carbonization=coalification – in which only the carbon remains in the specimen - other elements, like hydrogen, oxygen, and nitrogen are removed • recrystalization – hard parts either revert to more stable minerals or small crystals turn into larger crystals Homo sapiens (modern) 0.01 MY Evolution in action I – Industrial melanism • authigenic preservation – molds and casts of organisms that have been destroyed or dissolved Evolution in action II – Drug resistance in HIV • RT inhibitors – Block reverse transcription • Nucleotide RT inhibitors – Chain terminating nucleotide analogs – Some escape mutations avoid incorporating altered bases – Others can excise them if incorporated – In absence of drug modifications are deleterious Frequency of melanic form in England (1959-1995) Melanic and wild-type Biston betularia – Compensatory mutations can occur which reduce/remove deleterious effect Ring species Homology – inference of shared ancestry • • Continuously interbreeding forms between two or more separate species – e.g. Ensatina salamanders in California Structures similar by descent – wings of birds and bats homologous to arms of humans and flippers of dolphins – subunit alpha- and beta-globin in haemoglobin similar through descent 3D alignment of protein structures http://www.elcomsoft.com/3dpaln.html Is species change inevitable? Further controversies in the evolution debate I • Gradualist v punctuated? – Fossil record shows abrupt changes of form separated by long periods of stasis – ‘Punctuated Equilibrium’ – Gould and Eldridge Coelocanth – BUT fast in fossil record is millions of years – Fossil record very patchy – Gradualist evolution can occur fast (e.g. Homo sapiens) Dicksonia tree fern Tuatara Further controversies in the evolution debate II • The influence of physical properties – Is the course of evolution an emergent property of the nature of complex systems governed by simple laws? – Emergent properties/self-assembly