EVOLUTION: A History and a Process
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Transcript of EVOLUTION: A History and a Process
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EVOLUTION: A History and a Process
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Voyage of the Beagle During his travels, Darwin made numerous
observations and collected evidence that led him to propose a hypothesis about the way life changes over time.
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Darwin’s Observations Giant Tortoises of the Galápagos Islands
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Darwin’s Observations
Variety of finches
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• Jean-Baptiste Lamarck proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. These traits could then be passed on to their offspring. Over time, this process led to changes in a species.
Lamarck’s explanation of how evolution works was wrong, but it helped set the stage for Darwin’s ideas
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Others that influenced Darwin’s ideas Charles Lyell: explained that slow and
gradual processes have shaped Earth’s geological features over long periods of time.
Thomas Malthus: Populations can grow much faster than the rate at which supplies of food or other resources can be produced.
Alfred Wallace: Described same basic mechanisms for evolutionary change that Darwin had proposed.
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Darwin’s Two Main Points
Descent with modification: Descendants of earliest organisms accumulated adaptations to different ways of life.
Natural selection: The process by which individuals with inherited characteristics well-suited to the environment leave more offspring on average than other individuals
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Darwin’s Book
The Origin of Species (1859)
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Natural selection: The process by which individuals with inherited characteristics well-suited to the environment leave more offspring on average than other individuals
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Evidence of evolution
Darwin argued that living things have been evolving on Earth for millions of years. Evidence for this process could be found in:
the fossil record, the geographical distribution of living species homologous structures of living organisms, Vestigial structures, Similarities in early development, Molecular biology.
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Fossil Record Each layer of sedimentary rock
represents a time period. Fossil in each layer represent organisms that lived when the layer was formed
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Geographic Distribution of Living Species
Darwin decided that all Galápagos finches could have descended with modification from a common mainland ancestor.
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When pre-New Zealand split of from Australia, a new specie of birds called the "Kaka" evolved from its parrot-like ancestor. Then as new mountain ranges are formed in pre-New Zealand, these birds further evolve into two distinct specie: Lowland Kaka and Alpine Kea. Later, when pre-New Zealand split into two islands (which is now modern day New Zealand), the Lowland Kaka evolved into the North Island Kaka and the South Island Kaka.
EXAMPLE OF GEOGRAPHICAL DISTRIBUTION
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Homologous Body Structures
Structures that have different mature forms but develop from the same embryonic tissues are called homologous structures.
Similarities and differences in homologous structures help biologists group animals according to how recently they last shared a common ancestor.
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• Not all homologous structures serve important functions.
• The organs of many animals are so reduced in size that they are just vestiges, or traces, of homologous organs in other species.
• These organs are called vestigial organs.
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Similarities in Embryology
The early stages, or embryos, of many animals with backbones are very similar.
The same groups of embryonic cells develop in the same order and in similar patterns to produce the tissues and organs of all vertebrates.
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What about DNA
The use of Genetics and the knowledge of DNA has allowed for analysis of the similarities and differences between organisms. Common DNA sequences may support the theory that they share a common ancestor.
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Mendel + Darwin
Genetics Evolutionary biology
Change within populations
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What is microevolution?
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What is the gene pool of a population?
The sum total of all the alleles (alternative forms of genes) in all individuals that make up a population.
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Microevolution
Evolution based on genetic changes A generation-to-generation change in the
frequencies of alleles within a population
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Hardy-Weiberg equilibrium The frequency of alleles in the gene pool
of a population remain constant over time (in contrast to microevolution).
This equilibrium is not maintained in nature.
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What mechanisms can change a gene pool?
Genetic Drift (Chance) Bottleneck effect Founders effect
Natural selection (Chance & sorting)
Gene flow Mutation
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Genetic DriftChange in a gene pool of a population due to chance
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Effects of genetic drift in small populations: The bottleneck Effect
Natural disasters
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And The Founders Effect
A few individuals colonize an isolated island, lake, or some other new habitat.
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Gene Flow
Exchange of genes with other populations
Interbreeding increases variation in the population’s gene pool
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Mutations
Mutations carried by gametes enter the gene pool
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What leads to adaptation?
Natural selection – a blend of chance and sorting Chance - mutation & sexual recombination of alleles
lead to genetic variation in a population Sorting – differences in reproductive success among
members of the varying population
Genetic drift, gene flow, and mutation cause microevolution or changes in allele frequencies, but not adaptation
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Why does evolution matter today?
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Sickle Cell Disease & Malaria
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Finches of the Galapagos Islands
Food availability affected beak size(Peter and Rosemary Grant study)
Dry years – larger seeds available
Larger beaks are better
Wet years Smaller seeds available
Smaller beaks are better
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Homework
Give two examples of natural selection in action (Explain how it works)