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5.4 The Making of a Theory- Accounting for the Evidence

5.4 The Making of a Theory- Accounting for the Evidence. Prior to the 18 th Century, it was widely believed that living things were “fixed” and that they retained the same form when they first appeared on Earth.

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5.4 The Making of a Theory- Accounting for the Evidence

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  1. 5.4 The Making of a Theory- Accounting for the Evidence

  2. Prior to the 18th Century, it was widely believed that living things were “fixed” and that they retained the same form when they first appeared on Earth. • In the 1750's Georges-Louis Leclerc de Buffon, a naturalist, proposed two hypotheses to explain the distribution of plants and animals around the world: • Creation did not occur in one central place but there were numbers of “centers of creation.” • Species were not created perfectly and underwent changes over time. He later wondered if certain species were descended from a common ancestor.

  3. Similar views at this time • Carl Linnaeus • Few species at creation had become hybrids which formed new species • Erasmus Darwin (grandfather of Charles Darwin) • Life began from a single source

  4. A student of Buffon, Jean-Baptiste de Lamarck, theorized that organisms desiredto change for the better. • He reasoned that the use and disuse of certain structures could be passed on to the offspring.

  5. Lamarckism describes the concept of inheritance as acquired characteristics. • His main contribution to our understanding of evolution is that evolution is adaptive, and that the diversity of life is the result of adaptation.

  6. Almost half a century later, Charles Darwin published "On the Origin of Species by Means of Natural Selection" in 1859. • Alfred Wallace had sent Darwin a scientific paper prior to Darwin’s publication, describing his work. • Wallace had also come up with similar ideas to Darwin. Wallace insisted Darwin take the credit.

  7. It would take almost another century before other science disciplines (including genetics) could be integrated to form the modern theory of evolution – Neo-Darwinism.

  8. The road to a theory… • Darwin joined the crew of the HMS Beagleas the ship's chief naturalist in 1831. • Visiting some of the equatorial Galapagos Islands off South America, Darwin wondered at the differences in species between the islands.

  9. The road to a theory… • He paid particular attention to the differences among finches throughout the islands compared to the mainland finches. • Though they had similarities, the island finches had different shapes of beak depending on their geographic location

  10. Darwin spent years working on a theory to account for his observations - the Theory of Natural Selection. • What is a hypothesis? • A statement of what might be true, or an educated guess (based on evidence) and able to be contradicted, refuted, and/or rejected depending on the presence of new observations. • What is a theory? • A theory is a set of statements based on reasoning and evidence that explains a variety of observations. • Eg: quantum theory, theory of plate tectonics

  11. Evolution as a Hypothesis:"A Scientific fact is a hypothesis that is so firmly supported by the evidence that we assume it is true, and act as if it were true." • Darwin's great hypothesis was "descent, with modification, from common ancestors," or, simply, evolution. • It was an educated guess, deduced from many prior observations that explained much data and made predictions about future discoveries.

  12. Since it has been overwhelmingly supported, explains more data than even Darwin could imagine, and its predictions are extremely accurate, Evolution is accepted as scientific fact by experts in relevant areas of biology and geology. • Evolution is the unifying principle of modern biology.

  13. Theory of Natural Selection • Darwin’s theory can be divided into five distinct ideas: • Overproduction- the number of offspring produced by a species is greater than the number that can survive to reproduce. • Struggle for existence - competition for limited resources and habitat. • Variation- variations among a species are passed to the next generation. • Survival of the fittest (Natural Selection) - species with traits that give them a competitive advantage are better able to compete, survive and reproduce. All others die off. • Origin of new species (Speciation) - the accumulation of inherited variations generates a new species.

  14. Peppered Moth • http://www.youtube.com/watch?v=5NdMnlt2keE • http://www.youtube.com/watch?v=aTftyFboC_M

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