CHAPTER 16: DARWIN’S THEORY OF EVOLUTIONSection 16-2: Ideas the Shaped Darwin’s Thinking

AN ANCIENT, CHANGING EARTH

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

HUTTON AND GEOLOGICAL CHANGE

Connection between geological processes and features

Some rocks caused by sediments Earth shaped by natural forces Earth must be much older – deep time

LYELL’S PRINCIPLES OF GEOLOGY

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?

LAMARCK’S EVOLUTIONARY HYPOTHESIS

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

LAMARCK’S EVOLUTIONARY HYPOTHESIS

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

POPULATION GROWTH

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

ARTIFICIAL SELECTION

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