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amphibians: The class of vertebrates that contains the frogs, toads, newts, and salamanders.

The amphibians evolved in the Devonian period (about 370 million years ago) as the first vertebrates to occupy the land.

Peaks on the landscape correspond to genotypic frequencies at which the average fitness is high, valleys to genotypic frequencies at which the average fitness is low. adaptive logic: A behavior has adaptive logic if it tends to increase the number of offspring that an individual contributes to the next and following generations.

If such a behavior is even partly genetically determined, it will tend to become widespread in the population.

Species adapt when succeeding generations emphasize beneficial characteristics.antibiotic resistance: A heritable trait in microorganisms that enables them to survive in the presence of an antibiotic.aperture: Of a camera, the adjustable opening through which light passes to reach the film.artifact: An object made by humans that has been preserved and can be studied to learn about a particular time period.artificial selection: The process by which humans breed animals and cultivate crops to ensure that future generations have specific desirable characteristics.

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