C HAPTER 16: D ARWIN ’ S T HEORY OF E VOLUTION Section 16-2: Ideas the Shaped Darwin’s Thinking

A N A NCIENT, C HANGING E ARTH Many Europeans believed Earth was only a few thousand years old, had not changed much Geology was new Geologists James Hutton and Charles Lyell concluded that Earth is extremely old and that processes that changed Earth in the past also operate in the present

H UTTON AND G EOLOGICAL C HANGE Connection between geological processes and features Some rocks caused by sediments Earth shaped by natural forces Earth must be much older – deep time

L YELL ’ S P RINCIPLES OF G EOLOGY Argued laws of nature are constant over time, must use current, observable processes to explain past events Uniformitarianism Built on Hutton’s work Darwin read Lyell’s book while on the Beagle – witnessed a South American earth quake the proved Lyell to be correct If Earth had changed over time, could life change too?

L AMARCK ’ S E VOLUTIONARY H YPOTHESIS French naturalist who proposed two early hypotheses about evolution Suggested that organisms could change during their lifetimes by selectively using/not using various parts of their bodies Suggested individuals could pass these acquired traits on to their offspring, enabling species to change over time All organisms had an inborn urge to become more complex/perfect and changed or acquired characteristics to help them live more successfully

L AMARCK ’ S E VOLUTIONARY H YPOTHESIS Ex: Water birds acquired long legs because they waded into deeper water to look for food Called acquired characteristics Inheritance of acquired characteristics Link between body structures and environment Incorrect: No inborn drive to be “perfect” Evolution does not mean “becoming better” – no predetermined direction Acquired traits cannot be inherited

P OPULATION G ROWTH 1798  English economist Thomas Malthus noted humans were being born faster than people were dying, causing overcrowding If the human population grew unchecked, there would not be enough living space and food for everyone Forces like war, famine, disease work against population growth Darwin realized the same principle applies to all organisms – most offspring die before reaching maturity to reproduce

A RTIFICIAL S ELECTION Darwin looked for a natural, scientific explanation Studied change produced by plant/animal breeders Individual organisms vary, variations can be passed from parent to offspring