The Origin of Species, 1859
   "Descent with Modification"

Understanding Evolutionary time

Natural Selection link

Inductive Reasoning

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Dating the Earth (lec. 6)

1. Relative dating (stratigraphy)
2. Absolute dating (years)
• Sediment Depth: 2250 m ÷ 0.03 mm/yr = ?
• Sea Salt: 5x10¹⁶ tons ÷ 2.25x10⁸ tons/yr = ?
• Evolution: 300 traits ÷ 1 trait/10⁶yr = ?

Age of the Earth
Why is the Ocean Salty

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Absolute dating methods

• Historic records + p + g

• Tree Rings + + +

• Sediment Varves +

• Ice Cores + +

• Coral Layers +

• Cave Speleothems +

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Radiometric Dating

• Isotopes

• Decay

• Half-Life

• Radiocarbon Dating

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Darwin and the Scientific Method ?

4 Observations & 3 Conclusions

1. Populations have the potential to increase Exponentially

2. Populations are usually constant in size

"Lighten any check, mitigate the destruction ever so little, and the number of the species will almost instantaneously increase to any amount"

3. Natural resources are limited

    Conclusion #1

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Conclusion #1

Most organisms die leaving few or no offspring. There is a struggle for survival among individuals of a (interbreeding) population.

4. There is natural variation within a species, and the variation is inherited (Genghis Kahn, Charlemagne)

    Conclusion #2

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Conclusion #2

Those organisms with favorable (heritable) variations are more likely to survive and reproduce.

Conclusion #3

Accumulation of favorable variations over many generations (population) is natural selection. vs. artifical selection: 1855-68

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  I. MODIFICATION WITH DESCENT

 II. NATURAL SELECTION

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