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Natural Selection
Darwin’s Ideas
Setting the stage for Darwin
— Explaining the natural world in the Middle Ages
(≈ A. D. 400 - early 1500s)
º European worldview:
• Creation
• Fixity of Species
Great Chain of Being
• Age of Earth
As new data became available people
began to question old explanations
and develop new ones
Laying the foundation for Darwin
— Linnaeus
º Systema Naturae = classification system for all living organisms
• binomial nomenclature
— Lamarck
º Lamarckism = evolutionary explanation for change in species through time:
• Traits acquired by parents are inherited by their offspring = change in species through time
— Cuvier
º Catastrophism = metaphysical explanation for change in species through time
• Repeated creation events, each ended by a catastrophe.
— Lyell
º Uniformitarianism = geological explanation for formation of Earth’s features
• Geological forces that shape the Earth today have worked in the same fashion through time.
— Malthus
º An Essay on Principles of Population =
• Limiting environmental factors keep natural tendency for overproduction in check.
Darwin’s Natural Selection
— Proposed an evolutionary explanation for change in species through time (generation to generation):
º Within any species in a given environment the following will lead to change in a species:
1. Overproduction
¶ every generation more individuals are produced than can be supported by environment
2. Variation
¶ no 2 individuals are exactly alike
3. Selection of favorable variation
¶ those individuals more suited to environmental selective pressures have higher net
reproductive success, less suited will have lower net reproductive success
4. Inheritance of favorable variation
¶ traits selected for in previous generation will be more common in next generation
5. Evolution : Change in species through time
¶ as a result of natural selection acting on individual’s net reproductive success, later
generations may be distinctly different from earlier generations.