Evolution

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S. America, Llamas

Slide 36

Darwin’s Observations

Both Living Organisms & Fossils collected

Fossils included:

Trilobites

Giant Ground Sloth of South America

This species NO longer existed. What had happened to them?

Slide 37

Evidence for Evolution – The Fossil Record

Slide 38

Definition

Evolution is the slow , gradual change in a population of organisms over time

Slide 39

Darwin’s Observations

Left unchecked, the number of organisms of each species will increase exponentially, generation to generation

In nature, populations tend to remain stable in size

Environmental resources are limited

Slide 40

Darwin’s Conclusion

Production of more individuals than can be supported by the environment leads to a struggle for existence among individuals

Only a fraction of offspring survive each generation

Survival of the Fittest

Slide 41

Darwin’s Observations

Individuals of a population vary extensively in their characteristics with no two individuals being exactly alike.

Much of this variation between individuals is inheritable.

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Darwin’s Conclusion

Individuals who inherit characteristics most fit for their environment are likely to leave more offspring than less fit individuals

Called Natural Selection

Slide 43

The unequal ability of individuals to survive and reproduce leads to a gradual change in a population, with favorable characteristics accumulating over generations (natural selection)

New species evolve

Darwin’s Theory of Evolution

Slide 44

Ideas That Shaped Darwin’s Thinking

Thomas Malthus

Slide 45

Population Growth

Thomas Malthus, 1798

Economist

Observed Babies Being Born Faster Than People Were Dying

Population size limited by resources such as the Food Supply

Slide 46

The Struggle for Existence

Malthus’ Influence:

High Birth Rates & Limited Resources Would Force Life & Death Competition