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Organismic and Evolutionary Biology
Organismic and Evolutionary Biology OEB 53
Andrew Berry

OEB 53 SECTION NOTES 3 GREAT FACTS 1. Climate doesn’t explain everything Similar climates in different parts of the world have vastly different species...Darwin tries to promote the role of geography over the role of climate Argument against special creation: why create so many distinct/unrelated species to occupy similar habitats? 2. Barriers are important. Darwin notices early on that isolation is important in speciation: organisms have to be isolated so that they don’t mix with other organisms (equivalent to today’s ideas about allopatry) Examples of land barriers and oceanic barriers 3. Groups of related organisms confined to a specific region. Evidence against special creation: it would be redundant to populate similar niches around the world with different organisms DARWIN & DISPERSAL Darwin agrees with land bridges over shallow bodies of water, but does not agree that the continents had not been where they were in modern times. Model mostly relies on dispersal. Experiments: Molluscs on duck feet Idea of seeds migrating via birds (even if bird died, fell in water, drifted): stuffing dead pigeons with seeds, could seeds survive a long time in the water, still viable? Scattered seeds on the water: how many sunk and how many floated, calculated currents, distance Took mud from a pond, how much would germinate from it Darwin observed that on different mountaintops, there were the same species of plants. He hypothesizes that during the glacial period, ice sheets pushed seeds from north to the south, and then cold-adapted species retreated either north or up a mountain. Darwin notices similarity between island species and mainland species, supports descent with modification and dispersal ideas. Te
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