theory of evolution chapter 16 & 17. evolution change over time
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Theory of Evolution
Chapter 16 & 17
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Evolution
• change over time
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Acquired trait hypothesis
• Jean-Baptiste Lamarck proposed a theory that organisms pass on traits they acquire in their lifetime.
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Thomas Malthus• In 1798, English economist Thomas
Malthus noted that humans were being born faster than people were dying, causing overcrowding.
• Malthus believed:– if the human population grew unchecked,
there wouldn’t be enough living space and food for everyone
– the forces working against population growth included war, famine & disease.
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Natural Selection• Charles Darwin, a
naturalist, proposed a mechanism for explaining how evolution occurs
• During a voyage on the HMS Beagle, Darwin collected a vast amount of data, including the famous study of the finches on the Galapagos islands.
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• Aided by some ideas from Malthus, Lamarck, and his own studies, Darwin began suggesting the mechanism of natural selection.
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Evolution by Natural Selection
1. The Struggle for Existence:If more individuals are produced than can
survive, members of a population must compete to survive.
2. Variation & Adaptation:In a particular environment, some individuals of a population or species are better suited to survive
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3. Survival of the FittestOver time, the traits that make certain individuals able to survive and reproduce tend to spread in that population
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Evidence of Evolution1. Biogeography2. Fossils
– There is clear proof from fossils that living species evolved from older organisms
– homologous structures • Structures that are shared by related species and
that have been inherited from a common ancestor • Analogous Structures – share common function
but not structure• vestigial structures - structures that have no use
or are of little importance
3. DNA
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• Differences in DNA sequences are less between species that are more closely related
• Very important DNA sequences are highly conserved between species.
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• After over 25 years of research, Darwin published his ideas in his book The Origin of Species
• Darwin’s ideas are the basis for the latest insight on the evolution of species
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Adaptation
• the changing of a species that results in its being better suited to its environment
• enough change within a species eventually leads to a new species
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Speciation
• development of a new species
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• Isolation can lead to species formation
• Isolation is the condition in which 2 populations of the same species cannot breed with one another; therefore they do not share gene pools and variations can develop separately in each population that prevent them from interbreeding later.
• Ex: the Kaibab (north rim) and Abert (south rim) squirrels of the Grand Canyon
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Gradualism• speciation occurs
gradually
Punctuated Equilibrium• speciation occurs
rapidly between periods of little or no change
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5 Principle Evolutionary Forces
1. Mutation-the source of all variation, won’t significantly change allele frequencies except over long periods of time.
2. Gene Flow-migration allows for genes to move into and out of a population
3. Nonrandom Mating-mates with others nearby or with similar phenotype; inbreeding a type of nonrandom mating.
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4. Genetic Drift-a random event changes the frequency of an allele
5. Natural Selection-frequency of an allele will increase or decrease depending on allele’s effects on survival and reproduction
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Trait Distribution
• Normal distribution- (bell curve) average value at the summit
• Directional selection-entire curve shifts in one direction
• Stabilizing selection-individuals become more and more alike
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• Over long periods of time, events can occur that result in the species going extinct (disappear permanently)
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Overview of natural selection:
• All species have genetic variation
• The environment presents many different challenges to an individual’s ability to reproduce
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• Organisms tend to produce more offspring than a space can support, so individuals compete to survive
• Individuals that are better able to cope with the challenges of survival tend to leave more offspring than those who do not
• Traits of the individuals best suited to their environment tend to increase in the population over time