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Charles Darwin and the theory of natural selection Biology I
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I. Before Darwin Scientists knew that organisms had evolved Fossil evidence Age of the Earth
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I. Before Darwin Lamarck- aquired characteristics Evolve from simple to complex Organisms want to adapt
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I. Before Darwin Later disproved
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II. Darwin At 21, took a job as a naturalist on the HMS Beagle Collected specimens, took notes of different organisms
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His voyage:
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II. Darwin Sailed to Galapagos Islands All new species, but similar to those found elsewhere
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Finches most famous Had slightly different beaks from island to island Differed by their diet
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II. Darwin Darwin 22 years developing theory of natural selection Pressured into publishing by Wallace Published On the Origin of Species by Natural Selection
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III. Natural Selection 4 Requirements:Natural Selection 1. Variation 2. Differential Reproduction 3. Heredity 4.Lots of Time
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III. Natural Selection 1. Individuals have variations. –Color, size, speed, etc. The variations that natural selection acts on are genetically linked
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III. Natural Selection Four steps 2. Organisms produce more offspring than can survive –competition Only the best are going to survive
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III. Natural Selection 3. Beneficial variations survive, pass traits to offspring Passed through DNA
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III. Natural Selection 4. Over time variations become more frequent in population Results in population being different than ancestors
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III. Natural Selection Natural selection usually takes a long time Selection for a particular variation depends on environment
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Example of Natural Selection
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Evolution Evolution is the change in a population over time
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IV Evidence for Evolution Adaptations Anatomy Fossil Record Embryology Biochemistry
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Types of Adaptations An Adaptive Trait- variation that is helpful –Thick fur in cold places Maladaptive Trait- variation that is harmful –Poor eyesight
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Structural Adaptations Physical traits
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Mimicry-An adaptation Enables one species to resemble another species. Ex.-harmless species looks like a harmful one, good tasting vs. bad tasting.
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Camouflage-An adaptation A species blends in with its environment to avoid predators. Ex.- peppered moth, leaf frog
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Fossils Determine relationships among organisms. Ancestors of whales were probably land-dwelling, doglike animals.
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Anatomy- Homologous Structures Common evolutionary origin. Similar in arrangement or function or both. Example: forelimbs of a whale, a crocodile and a bird wing.
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Anatomy- Analogous Structures No common evolutionary origin, but similar in function. Wings of a bat and wings of a butterfly.
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Anatomy- Vestigial Structures No function now but was probably useful to an ancestor. Ex. A whale has leg bones, a snake has leg bones, we have a tail bone and wisdom teeth.
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Embryology Earliest stage of growth and development Embryos of a fish, a chicken, a pig, a cow, a rabbit, and a human are almost identical. They all have gill slits and a tail.
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Biochemistry Comparisons of DNA and RNA Now monera is divided into two separate kingdoms based on their biochemistry.
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V. Mechanisms of Evolution Genetic Drift Gene Flow Artificial Selection Natural Selection Sexual Selection
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Genetic Drift Change in allele frequency by CHANCE
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Gene Flow Change in allele frequency as a result of MIGRATION
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Artificial Selection Humans choose desired traits and manipulate breeding
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Sexual Selection Special case of Natural Selection Variations selected for their ability to attract a mate
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Geographic isolation Physical barrier divides a population New selective pressures Two different species
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Reproductive isolation No longer able to mate Different genetic information Mating behavior differences
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Selective Pressures Environmental Examples: drought, lack of food, extreme temperatures, predation
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Sources of Variation GENE FLOW moves genes among populations SEXUAL REPRODUCTION introduces new gene combinations Random MUTATIONS in DNA lead to the formation of new alleles (sound familiar?)
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Mutations Can be beneficial, neutral, or harmful for the organism Only mutations in gametes are inherited by offspring
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VI. Natural selection affecting populations Three major types of natural selection are: –Stabilizing Selection –Directional Selection –Disruptive Selection
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Stabilizing selection Average individual is selected for
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Directional selection One extreme trait is selected for
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Disruptive Selection Both extremes are selected for Average selected against.
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How do we determine a new species? A species is considered a group of organisms that can: 1.Interbreed 2.Produce Fertile offspring Two species of meadowlark
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