darwin’s theory of evolution 16.3 and 16.4. natural selection the process by which organisms with...
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Darwin’s Theory of Evolution
16.3 and 16.4
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Natural Selection• The process by which organisms with
variations most suited to their local environment survive and leave more offspring.
• Operates like artificial selection, but occurs IN NATURE.
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When Does Natural Selection Occur?
1. When more organisms are born than can survive (the carrying capacity has been reached).
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When Does Natural Selection Occur?
2. When there is natural heritable variation and adaptation.
An adaptation is a heritable characteristic that increases an organism’s ability to survive.
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When Does Natural Selection Occur?
3. There is variable fitness among individuals.High fitness- adaptations suitable to the
environment, can survive and reproduce.Survival of the fittest
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Common Descent: Evolutionary Trees
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Evidence That Supports Evolution Theory
F- fossilsA- anatomical structuresM- molecular evidenceE- embryological evidence
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Support for Evolution 1: Fossils/Age of Earth
• Earth is 4.5 billion years old according to radioactive dating.
• Paleontologists have recently discovered fossils that form a series that traces the evolution of modern species from extinct ancestors.– Examples: whales from land mammals, birds from
dinosaurs, fish from four-legged land animals.
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Types of Whales
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Whale Evolution Theory
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Support for Evolution 2: Anatomical Structures
• Homologous structures are shared by related species and have been inherited from a common ancestor.– Results from descent with modification from a
common ancestor.
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Analogous Structures• Analogous structures are body parts that
share a common function, but not structure.
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Vestigial Structures• Vestigial structures are inherited from
ancestors but have lost much or all of their original function due to different selective pressures.– Example: hip bones in dolphins
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Support for Evolution 3: Molecular Biology
• Universal genetic code and homologous molecules.
• Examples: cytochrome c, Hox genes
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Support for Evolution 4: Embryology
• Similar patterns of embryological development.
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Testing Natural Selection• This is difficult because evolution takes
millions of years. • Peter and Rosemary Grant have spent 35 years
studying the Galapagos finches.– Natural selection takes place in wild finch
populations frequently and sometimes rapidly.– Variation within a species increases the likelihood
that the species can adapt to and survive environmental change.
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Modern Example of Evolution: Antibiotic Resistance and Superbugs