1. Outline 15-3A: Darwin’s Theory of Natural Selection
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Outline 15-3A: Darwin’s Theory of Natural Selection

2. I. Darwin’s Mechanism for Evolution
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I. Darwin’s Mechanism for Evolution
A. Darwin proposed a mechanism for evolution called natural selection.
B. This was based on:
1. His observations in the Galapagos Islands
2. His own, and others, research in plant and animal breeding.
3. Fossil evidence from around the world
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3. II. Darwin Published His Ideas
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II. Darwin Published His Ideas
A. He worked on his ideas for over years.
B. In 1858, Alfred Wallace sent him an essay much like his own theory.
C. In 1859, Darwin published his book On the Origin of Species by Means of Natural Selection
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4. III. Natural Selection’s 6 elements:
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III. Natural Selection’s 6 elements:
A. Variation exists among individuals of a species
1. Darwin argued that this variation was very important
2. Plant & animal breeders used variation to improve crops & animals
a. Chose largest hogs, fastest horses, etc. in order to produce what they wanted. This is called artificial selection.
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5. Inherited Variation and Artificial Selection
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Cauliflower
Brussels Sprouts
Broccoli
In artificial selection, humans select from among the naturally occurring genetic variations in a species. From a single ancestral plant, breeders selecting for enlarged flower buds, leaf buds, leaves, or stems have produced all these plants.
Ancestral Species
Kohlrabi
Kale

6. B. The Struggle for Existence
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B. The Struggle for Existence
1. The environment presents challenges to an individual’s ability to survive and reproduce
2. Members of each species compete to obtain food, water, shelter, mates, etc.
C. More offspring are produced than their environment can support
1. As individuals compete with one another some will live; some will die
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7. D. Adaptations help in survival
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D. Adaptations help in survival
1. An adaptation is a characteristic that helps an organism survive
a. Adaptations can be anatomical, physiological, or behavioral characteristics
2. Individuals with good adaptations are more likely to grow up & reproduce They will tend to leave more offspring than those less well adapted. They have greater fitness.
a. Darwin called this survival of the fittest.
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8. E. Over many generations, the. population changes (evolves) to
E. Over many generations, the population changes (evolves) to become more like the well adapted individuals Since humans are not directing this process Darwin referred to it as natural selection.
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9. F. Descent with Modification. 1. Natural selection produces
F. Descent with Modification Natural selection produces organisms that have different structures & occupy different habitats Each living species has descended, with changes, from other species over time This implies that all living organisms are related to one another. This is known as common descent.
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10. How can you explain the evolution of
How can you explain the evolution of long necks in giraffes by the process of natural selection instead of Lamarck’s idea of Inheritance of Acquired Characteristics? Hint: Do NOT use the words “needed” or “tried to change” in the explanation
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