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Natural Selection and Evolution Assumptions of Darwin 1. offspring vary 2. some of this variation is heritable 3. more offspring are born than can survive 4. populations do not generally increase in size Inferences of Darwin 1. individuals of the same species will compete 2. the survivors will pass on their ‘favourable’ traits to the next generation 3. over time there will be more traits from the survivors in the population … This is natural selection. Examples of Natural Selection a leaf-like praying mantis peppered moths in pre- and postindustrial England mimicry of the poisonous coral snake by the nonpoisonous king snake Darwin mistakenly believed that giraffe neck length was an example of natural selection some baby giraffes are born with slightly longer necks there is limited food, so longer-necked giraffes get more food and survive better over time the population would consist of longer-necked giraffes but Darwin was WRONG giraffes spend more time eating low leaves, not high leaves bending down to get a drink is awkward Why do giraffes need long necks? males fighting males this is an example of sexual selection Homologous vs. Analogous vs. Vestigial Features homologous structures: similar strucures doing very different functions analogous structures: different structures doing very similar functions vestigial structures: structures with no function in one organism, but have a function in similar organisms Macroevolution vs. Microevolution Macroevolution large scale evolutionary change significant enough to warrant the classification of groups or lineages into distinct genera or even higher-level taxa i.e. many species arising from one common ancestor takes a very long time (10,000’s to millions of years) e.g. evolution of birds or mammals e.g. Darwin’s finches Microevolution: changes in gene (allele) frequencies and phenotypic traits within populations and species; can result in the formation of new species i.e. change within a species takes less time (10’s to 1000’s of years) e.g. antibiotic-resistance in bacteria