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Evoluzione: i concetti chiave The Origin of Species • • • Evolution is the explanation for life’s unity and diversity Natural selection is the mechanism 3 inferences based on 5 basic observations * * * Too many individuals for limited resources Those with better traits survive and reproduce Their traits dominate in population and cause it to evolve Too many individuals for limited resources • • In populations, more individuals are born than can be supported by the environment Only a fraction will survive to the next generation (there is a struggle for existence) Observation 1 Fig 22.8 • • Species have great powers of potential reproduction Populations would increase exponentially if all individuals survived and reproduced Observation 2 • But populations tend to remain stable over time, except for seasonal fluctuations Fig 52.17 Moose population on island in Lake Superior Observation 3 • • Environmental resources are limited Discussion in Malthus, “Essay on the Principle of Population” helped clarify this ~ Fig 52.19 Lucky Lynx and its 1 hare Those with better traits survive and reproduce • • • Struggle for existence is not random Depends on an organism’s characters that are, at least in part, hereditary More fit individuals will leave more offspring than less fit individuals Observation 4 • Individuals in a population vary extensively Fig 22.9 Observation 5 • • Much of this variation is heritable However, Darwin did not know the mechanism Fig 1.3b Their traits dominate in a population and cause it to evolve • • Unequal ability of individuals to survive and reproduce leads to gradual change in a population More favorable characters accumulate microevolution! Peter and Rosemary Grant have been working on Galapagos finches since 1973 on Isla Daphne Major. Geospiza fortis is a seed-eater that cracks seeds by grasping at the base of the bill and applying force. Beak size is correlated with consumed seed size. Are characteristics variable in a population? YES. Is some of the variation among individuals heritable? YES. Is there an excess of offspring such that only some individuals survive to reproduce? YES. Is survival and reproduction nonrandom? YES. Other Evidence for Evolution • Organisms are adapted to their environments Fig 22.10a A floral mantid on a flower. Please look at the entire figure in the text Other evidence • Artificial selection Fig 22.11b Vegetables selected by humans from wild “kole” Other evidence • Examples of natural selection Fig 22.12 Evolution of resistance to insecticides in insect populations Other evidence • Homologous structures Fig 22.14 Forearm bones in mammals • Other evidence Molecular “record” – molecular homologies Fig 17.16 Ribosomal structure (large subunit of bacterial ribosome) Other evidence • Biogeography Fig 34.32 Adaptive radiation of Australian marsupials compared to similarities among other mammals • Other evidence Fossil record Fig 22.7 Elephant evolution based on fossils Fossil Trilobites Transitional fossils Microevolution - generational changes in the characteristics of a population Macroevolution - origin of new species and other taxonomic groups due to accumulation of change over long periods of time. L’evoluzione ha la VISTA lunga… Le forze motrici dell’evoluzione: V I S T A variation (variazione) inheritance (ereditarieta’) selection (selezione) time (tempo) adaptation (adattamento)