Lecture II - Darwinian Natural Selection

Lecture II - Darwinian Natural Selection - Lecture II -...

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Unformatted text preview: Lecture II - Darwinian Natural Selection Darwin's Four Basic Postulates • Individuals within a population vary in their traits • These variations are passed from parent to offspring (hereditable) • Some individuals are more successful at surviving and reproducing than others • Survival and reproduction are related to the variation in traits among individuals. Darwin’s Inspirations • Many things inspired Darwin toward developing his theory of natural selection • However, the two strongest inspirations were: • Patterns observed in nature • Artificial selection Patterns Observed in Nature • During his five-year journey aboard the Beagle, Darwin observed and collected thousands of specimens of plants, animals, fossils Natural Phenomena – Island Populations Cape Verde Islands Galápagos Islands Natural Phenomena – Island Populations Variation in Giant Tortoises Robert H. Rothman © Giant Galápagos Tortoises Darwin's Finches • There are 15 closely- related species native to the Galápagos Islands • Now known to evolved from a single ancestor 2–3 million years ago Darwin’s Finches Darwin’s Finches • These finches vary both in beak size and diet • The beak sizes and shapes are suited to each bird's diet • Assumption: natural selection played a role in beak size evolution Natural Phenomena – Island Populations • Habitats on the islands differ in some ways from those on the mainland • The different islands each have their own characteristic habitat features • Species on islands are similar to, but not the same as, those on the mainland. • Each island has species similar to those on the other islands, but not the same. Island Populations • Being so similar to mainland species, perhaps island organisms originated on the mainland, and changed to fit diverse island habitats? • To quote: “Seeing this gradation and diversity of structure...one might fancy that...one species has been taken and modified for different ends” (Journal of Researches, 1842) Decent… with Modification? • So, if island flora and fauna came from the mainland, and • Island species have diverged from those on the mainland, and • Diversification has occurred among the islands, resulting in many species suited to diverse habitats, • Then: species change – descent with modification from a single ancestral species Artificial Selection • Darwin spent many years breeding a large assortment of domesticated animals • He knew that through selection of particular...
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This note was uploaded on 01/23/2010 for the course BIOS 230 taught by Professor Gibbons during the Fall '08 term at Ill. Chicago.

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Lecture II - Darwinian Natural Selection - Lecture II -...

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