Chapter 18 – Evolution Read the chapter before class! • Main conclusion is that “today’s organisms descended, with modification, from ancestors that lived in the past” – the fossil record supports this concept • Biologists do NOT claim to be able to explain the origin of life on earth
The term “THEORY” • Certain words have very precise meanings in science, different from “normal” meanings: – “Hypothesis” a reasonable guess, based on some evidence, to explain something. – “Theory” a hypothesis for which the evidence is overwhelmingly convincing so that it is accepted generally as the correct explanation. It can be tested and so far has not been disproved although that is always possible! Explains “why”. Example: the Theory of Plate Tectonics – “Law” always seem to work, never contradicted by evidence, enables predictions but doesn’t explain “why”. Example: The law of gravity. Newton had no good Theory of gravity. • • Note: It may always be possible to disprove Hypotheses and Theories, but they can never be finally proven.
Scientific Method 1. Make observations 2. Come up with one or even several possible hypotheses to explain the observations 1. Test the hypotheses (experiments, new observations) 2. Accept/reject hypotheses based on the test results 3. Repeat 3 and 4 until the hypothesis becomes a theory or gets rejected. • •
What is organic evolution? ,
Early ideas (pre-Darwin) Baron Georges Cuvier (1769-1832) multiple extinctions (multiple catastrophes) followed by new species: Noah’s Flood was only the most recent of these catastrophes.
Early ideas (pre-Darwin) Erasmus Darwin (1731-1802) – Charles’ Grandfather Suggested evolution – transmutation - of simple species to complex ones but didn’t include Natural Selection (although he came close) “Would it be too bold to imagine that, in the great length of time since the earth began to exist, perhaps millions of ages before the commencement of the history of mankind would it be too bold to imagine that all warm- blooded animals have arisen from one living filament, which the great First Cause endued with animality, with the power of acquiring new parts, attended with new propensities, directed by irritations, sensations, volitions and associations, and thus possessing the faculty of
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