CHANGES OVER TIME. Unit Preview Darwin’s Theory Evidence of Evolution The Fossil Record.
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Transcript of CHANGES OVER TIME. Unit Preview Darwin’s Theory Evidence of Evolution The Fossil Record.
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CHANGES OVER TIME
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Unit Preview
• Darwin’s Theory
• Evidence of Evolution
• The Fossil Record
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Darwin’s Theory
• What important observations did Darwin make on his voyage?
• What hypothesis did Darwin make to explain the differences between similar species?
• How does natural selection lead to evolution?
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Key Terms
Adaptation -
Evolution -
Fossil -
A trait that helps an organism survive and reproduce.
The gradual change in a species over time.
The preserved remains or traces of an organism that lived in the past.
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Key Terms
• Natural Selection -
• Scientific Theory -
• Species -
• Variation -
Individuals that are better adapted to their environment are more likely to survive.
A well-tested concept that explains a wide range of observations.
A group of similar organisms that can mate with each other and produce offspring.
Any difference between individuals of the same species.
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Charles Darwin
• A “naturalist” – studied the natural world.
• Sailed on the Beagle to the Galapagos Islands.
• Observed many unusual organisms on the island.– Giant tortoises– Blue-footed booby– Galapagos finches
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The Voyage of the Beagle
• The Beagle made many stops along the coast of South America stopping at the Galapagos Islands.
• Darwin observed living things as he traveled and tried to make connections about the relationships among those organisms. – Diversity of living things– Remains of ancient organisms– Unique characteristics of organisms on the
Galapagos.
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Darwin’s Observations
• The theory of EVOLUTION by NATURAL SELECTION
• Evolution – The gradual change in a
species over time.
• Natural Selection– Individuals that are
better adapted to their environment will survive and reproduce.
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DIVERSITY
• The variety of life on Earth.
• Darwin was amazed by the tremendous diversity of living things that he saw.
• Scientists have identified more than 1.7 million species of organisms on Earth.
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FOSSILS• The preserved
remains or traces of an organism that lived in the past.
• Darwin was puzzled by some of the fossils he observed.
• He saw fossil bones of animals that had died long ago but yet resembled the bones of organisms alive in Darwin’s time.
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Galapagos Organisms
• Darwin observed many unusual life forms on these small islands.
• He compared Galapagos organisms to organisms that lived elsewhere.
• He also compared organisms on different islands in the Galapagos group.
• He tried to make connections using the similarities and differences he observed.
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Comparisons to South American Organisms
• The Galapagos organisms resembled many of those in South America.
• Important differences between the organisms on the islands and those on the mainland were important in determining how the species ended up on the islands.
• Darwin hypothesized that a small number of different plant and animal species had come to the Galapagos Islands from the mainland.– Blown out to sea during a storm– Set adrift on a fallen log
• Once on the islands, the organisms reproduced and over time, their offspring became different from their mainland relatives because of their environment.
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IGUANAS
• The iguanas on the Galapagos Islands had large claws.– Grip slippery rocks– Feed on seaweed
• The iguanas on the mainland had smaller claws.– Climb trees– Eat leaves
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Comparisons Among the Islands
• Darwin noticed many differences among organisms as he traveled from one island to the next.
• Darwin was able to identify which island an organism came from just by looking at it.
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TORTOISES
• Some had dome-shaped shells.
• Some had saddle-shaped shells.
• Tortoises lived inland and became like “land-dwelling mammals” grazing on vegetation.
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GALAPAGOS FINCHES
• Each species was well ADAPTED (suited) to the life it led.
• Beak shape was based on their diet. – Narrow, needle-like
beaks = insects– Strong, wide beaks
= seeds
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Adaptive Radiation• The evolutionary diversification of a single
lineage into a variety of species with different adaptive properties.
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Theory of Evolution
• Darwin spent 20 years consulting with other scientists, gathering more information, and re-evaluating his observations from his trip on the Beagle before he
developed his theory of evolution.
• Plants or animals faced with different conditions will gradually change over many generations in order to
become better adapted to their conditions.
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Selective Breeding
• The process of selecting a few organisms with desired traits to serve as parents of the next generation.
• By repeatedly allowing only organisms with the desired traits to reproduce, the more desirable trait becomes common and highly favorable in the offspring.
• Darwin made connections between the practice of selective breeding and organism behavior in nature as evidence for his theory of evolution.
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Natural Selection
• In 1858, Darwin proposed an explanation for how evolution could occur in nature.
• Evolution occurs by means of NATURAL SELECTION.
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Natural selection is the 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 the Process of Natural Selection
• Overproduction
• Variations
• Competition
• Selection
• Environmental change
• Genes
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OVERPRODUCTION
• Most species produce far more offspring than can possibly survive.
• A large number of offspring creates competition for resources.
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VARIATIONS
• Members of a species differ from one another in many of their traits.
• Variations are linked to environmental conditions.
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COMPETITION
• Limited resources creates competition among members of a species.
• Direct– Physical fights
• Indirect– Searching for food– Avoiding predation
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SELECTION
• Some variations make individuals better adapted to their environment.
• Individuals who are better adapted survive and reproduce.
• Helpful variations may gradually accumulate in a species, while unfavorable ones may disappear.
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ENVIRONMENTAL CHANGE
• A change in the environment can affect an organism’s ability to survive.
• The environmental change can gradually lead to selection.
• The Galapagos Islands are a prime example of how the environment can lead to the evolution of a species by natural selection.
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GENES
• Without variations, all the members of a species would have the same traits.
• Natural selection would not occur because all the individuals would have an equal chance of surviving and reproducing.
• Variations can result from mutation and the shuffling of alleles during meiosis.
• Genes are passed from parents to offspring.
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Natural Selection . . .
. . . Survival of the Fittest!