Presentation on theme: "Evolution Biological changes over time Vocabulary Species – a population of organisms that can produce healthy, fertile offspring. Adaptation – inherited."— Presentation transcript:
Vocabulary Species – a population of organisms that can produce healthy, fertile offspring. Adaptation – inherited trait that increases chance of survival. Niche – a specific habitat, and the role a population plays in it.
Variation – differences between individuals in a population. Speciation – evolution of one or more species from a common ancestor species. Fossils – preserved remains or imprints of ancient organisms
Darwin’s Trip to the Galapagos Islands Observed the finches on the islands and noticed each had its own niche. There were 13 different species of finches, and each had adapted to its own niche. Concluded that adaptations had led to new species emerging.
Natural Selection Natural variations exist within species, and they can be inherited. Some of these variations are favorable. They increase the ability to survive. All offspring born cannot survive. Individuals that survive to reproduce have favorable traits.
Figure 24.13 Gradualism model. Species descended from a common ancestor gradually diverge more and more in their morphology as they acquire unique adaptations. Time (a) Punctuated equilibrium model. A new species changes most as it buds from a parent species and then changes little for the rest of its existence. (b)
Rate of Evolution Gradualism – Evolution occurs at a very slow rate. Small genetic changes in populations over many generations. Punctuated Equilibrium – Populations remain stable for long periods of time, with brief periods of rapid genetic changes.
Types of Evolution Convergent evolution – different species develop similar adaptations in response to similar environments.
Adaptive Radiation Evolution of many differently adapted species from one common ancestor species. As populations separate and occupy new niches, they will evolve different adaptations. Examples: Galapagos finches.
Fig 23.12 A–C (a) Directional selection shifts the overall makeup of the population by favoring variants at one extreme of the distribution. In this case, darker mice are favored because they live among dark rocks and a darker fur color conceals them from predators. (b) Disruptive selection favors variants at both ends of the distribution. These mice have colonized a patchy habitat made up of light and dark rocks, with the result that mice of an intermediate color are at a disadvantage. (c) Stabilizing selection removes extreme variants from the population and preserves intermediate types. If the environment consists of rocks of an intermediate color, both light and dark mice will be selected against. Phenotypes (fur color) Original population Original population Evolved population Frequency of individuals
Directional selection – change in genetic frequencies in response to specific environmental changes. An existing adaptation may no longer be beneficial. A new adaptation may become more dominant with time.
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