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Transcript
26/09/2016 In this lecture: Darwin’s Ideas A reminder • Evolution is not just natural selection. • Sexual selection and genetic drift are major players in natural populations, and artificial selection in domesticated ones. Darwin • The Origin was really only a precis (even at 400 pages!). • This was a short version to prempt Wallace, but why did he take decades to accumulate evidence? • Take 2 minutes to think. • • • • Darwin’s evidence for natural selection Support from genetics The modern synthesis In the future? Natural selection • This leads to adaptive change. The environment, predators, diseases etc. will affect a population and lead to differential survival / reproduction and so also change. • Situations change! What works now may not work later. Evolution can’t predict the future. • It doesn’t want or need things, selection acts. Why the wait? • Expected resistance from the church as a challenge to the creation story. • Resistance from other scientists. • Resistance from his wife. 1 26/09/2016 Darwin’s Evidence • • • • • Fossil Record • Fossils do not appear in a random order. Simple forms are older, more complex animals are more recent. 1. The Fossil Record 2. Comparative Anatomy 3. Embryology 4. Vestigial Structures 5. Domestication (artificial selection) Comparative anatomy • Organisms share major features suggesting they are related. • This is true even when they have different functions. Analogy example Homology vs Analogy • Analogy (same function, different structure) • Homology (same structure, may be different function) • Can you suggest examples? • Take 2 minutes. Homology example • Implies convergence 2 26/09/2016 Embryology Vestigial structures • Remnants of structures no longer in use. • Evidence of ancestry and change over time. • Embryonic retention of ancestral characters (e.g. gills, tail). Variation under Domestication Artificial Selection • With no direct observations of natural selection available Darwin turned to domestic animals. • Much of the book is devoted to discussions of artificial selection (dogs, horses, chickens and especially pigeons). • Why? • This is superb evidence for natural selection as it shows: variation was naturally occurring characters were inherited selection could favour certain traits • Therefore this could be applied to living systems where the selection was natural. Domestication • Some ‘extreme’ traits could be produced in a few generations from normal pigeons. • This was true of many different lineages and would be familiar to much of the audience. 3 26/09/2016 Problems Brassica oleracea • Darwin’s arguments were based on much logic and interpretation rather than hard evidence. • He was working at a time when there was little hard natural science. • We had few fossils, limited knowledge of species from outside Europe and no understanding of inheritance. • Darwin was aware of the limitations of the data and theory and even devoted a chapter to them. Critics • Darwin faced major critics at the time. • This culminated in a debate at Oxford that was largely a draw. • Many scientists however strongly supported Darwin’s case. Since Darwin • Huge amount of evidence have been added to corroborate his fundamental ideas, but also extend them greatly. • Additional data from: inheritance, fossils, development, direct observations. • This culminated in the ‘modern synthesis’ with the integration of genetics. • Moving from the ‘fact’ (evolution happens) to the ‘mechanism’ (how and why). And where are we now ? Gregor Mendel (1822-1884) • Austrian monk. • Worked out the basic laws of inheritance. 4 26/09/2016 Watson & Crick R.A. Fisher (1890-1962) "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material." J.B.S. Haldane (1892-1964) • With Fisher and Wright, one of the founders of population genetics. • “The Causes of Evolution” (1932): first major contribution to what became the modern evolutionary synthesis. Ernst Mayr (1904-2005) • Worked on methods of speciation. • Gave the ‘biological species concept’ definition of species. • Invented Analysis of Variance and other statistical tools. • Theory of population genetics. Theodosius Dobzhansky (1900-1975) • “Nothing in Biology makes sense except in the light of evolution”. • Genetics and the Origin of Species, published in 1937. William D. Hamilton (1936 - 2000) • Explained how sex ratios can deviate. • Explained how natural selection acts on social behaviour (“kin selection”). 5 26/09/2016 Summary John Maynard-Smith (1920-2004) • Most widely known for: • applying game theory to evolutionary biology • the two-fold cost of sex 1. finding a mate 2. only ♀ have babies What next? • EVOLUTION - “descent with modification” • Integrates data from: • • • • • Fossil record Dating methods Molecular evolution Molecular clocks Population genetics • Environmental drivers climate continental drift extinctions... Conclusions • Epigenetics • Cultural transmission • Niche construction “Extended Evolutionary Synthesis” ? • Evodevo • Comparative genomics • Systems Biology “Postmodern Synthesis” ? • Darwin initially had limited evidence for his theory but huge leaps in the last century have integrated major areas of biology to support it. • Involves genetics, behaviour (especially social structures), embryology, and issues of relatedness. • Natural selection is extremely well supported. Further Reading • http://erwan.lageat.free.fr/R1/Articles/Article s%20nature/Crick%20and%20Watson%20195 3.doc • http://users.ox.ac.uk/~jrlucas/legend.html • http://www.ncbi.nlm.nih.gov/books/NBK1012 8/ 6