Natural selection

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This means “No Change” or “No Evolution”.

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Macroevolution

The origin of taxonomic groups higher than the species level.

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Microevolution

A change in a population’s gene pool over a secession of generations.

Evolutionary changes in species over relatively brief periods of geological time.

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Five Mechanisms of Microevolution

1. Genetic drift:

Change in the gene pool of a small population due to chance.

Two examples:

a. Bottleneck effect

b. Founder effect

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a. Bottleneck Effect

Genetic drift (reduction of alleles in a population) resulting from a disaster that drastically reduces population size.

Examples:

1. Earthquakes

2. Volcano’s

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b. Founder Effect

Genetic drift resulting from the colonization of a new location by a small number of individuals.

Results in random change of the gene pool.

Example:

1. Islands (first Darwin finch)

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Five Mechanisms of Microevolution

2. Gene Flow:

The gain or loss of alleles from a population by the movement of individuals or gametes.

Immigration or emigration.

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Five Mechanisms of Microevolution

3. Mutation:

Change in an organism’s DNA that creates a new allele.

4. Non-random mating:

The selection of mates other than by chance.

5. Natural selection:

Differential reproduction.

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Modes of Action

Natural selection has three modes of action:

1. Stabilizing selection

2. Directional selection

3. Diversifying selection

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1. Stabilizing Selection

Acts upon extremes and favors the intermediate.

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2. Directional Selection

Favors variants of one extreme.

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3. Diversifying Selection

Favors variants of opposite extremes.

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Speciation

The evolution of new species.