Darwin’s Voyage. Darwin’s Observations As Darwin traveled around the world on a British naval...
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![Page 1: Darwin’s Voyage. Darwin’s Observations As Darwin traveled around the world on a British naval ship, he was amazed by the incredible diversity of the.](https://reader033.fdocuments.net/reader033/viewer/2022042616/56649e805503460f94b84820/html5/thumbnails/1.jpg)
Darwin’s Voyage
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Darwin’s Voyage
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Darwin’s Observations
• As Darwin traveled around the world on a British naval ship, he was amazed by the incredible diversity of the organisms or species that he saw.
• Species– A group of similar organisms that can mate
with each other and produce fertile offspring.
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Galapagos Island & South America
• Darwin was surprised that many of the plants and animals were similar to organisms on mainland South America, yet there were also important differences.
• Darwin inferred that a small number of different species had come to the island from the mainland and that eventually their offspring became different from the mainland relatives.
• Adaptation– A trait that helps an organism survive and reproduce.– Ex. Beak shape and size differences in the finches
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Darwin’s Finches
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Evolution
• Evolution– The gradual change in species over many
generations in order to become better adapted to the environmental conditions.
– Darwin proposed that evolution occurs by natural selection.
• Natural Selection– Process by which individuals that are better adapted
to their environment are more likely to survive and reproduce than other members of the same species.
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Factors Affecting Natural Selection
• Overpopulation– Most species produce far more individuals than can
possibly survive.• Competition
– Offspring must compete for food and other resources to survive.
• Variations– Difference between individuals of the same species.
• Selection– Some variations make certain individuals better
adapted to their environment.– These will survive and reproduce, thus possibly
passing this allele onto their offspring.
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Types of Selection
• Stabilizing Selection– Natural selection favors average individuals.– Reduces variation in a population.
• Directional Selection– Natural selection favors one of the extreme variations
of a trait.– Leads to rapid evolution of a population.
• Disruptive Selection– Favors both extreme variations of trait– Results eventually in no intermediate forms of the trait
and leads to the evolution of two new species.
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Relating Natural Selection to Evolution
• Over a long period of time, natural selection can lead to evolution.
• Helpful variations gradually accumulate in a species, while unfavorable ones disappear.
• Ex. Faster turtles will be able to escape predators and thus might pass this trait onto their offspring. This species might then be marked by the “fast-swimmer” trait.
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Role of Genes in Evolution
• NOTE: Only traits that are inherited, or controlled by genes, can be acted upon by natural selection.
• Ex. Color in moths during the Industrial Revolution
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How Do New Species Form?
• Geographic Isolation– New species can form when a group of
individuals remains separated from the rest of its species long enough to evolve different traits.
– Ex. Kaibab vs. Abert’s Squirrel
• Continental Drift Theory– Emphasizes that Pangea breaking apart
resulted in geographic isolation which led to evolution of various species
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Development of New Species
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Patterns of Evolution
• Divergent Evolution– Pattern of evolution in which species that once were
similar to an ancestral species diverge, or become increasingly different
– Caused by populations adapting to different environmental conditions and eventually resulting in new species
• Convergent Evolution– Pattern of evolution in which unrelated species evolve
similar traits because they occupy similar environments in different parts of the world.
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The Flip Side of the Coin
• Mutations or changes in the DNA are rarely helpful but are usually neutral, harmful, or fatal.
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Summary Questions
• What is evolution? What did Darwin observe on the Galapagos Islands that he thought was the result of evolution?
• Explain why variations are needed for natural selection to occur.
• Describe how geographic isolation can result in the formation of a new species.
• Some insects look just like sticks. How could this be an advantage to the insects? How could this trait have evolved through natural selection?