Unit VI - Evolution ~ a unifying theme of biology ~
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Transcript of Unit VI - Evolution ~ a unifying theme of biology ~
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Unit VI - Evolution
~ a unifying theme of biology ~
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Introduction to Evolution
• What does biological “evolution” mean?– Change in organisms over time
• How does this relate to the “origin of life”?– It doesn’t…two different topics!– Much more evidence to support evolution– Remember: science deals with natural world,
not belief
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Introduction to Evolution
• How could “life” have started?– Old Idea:
• “spontaneous generation” (abiogenesis)…nonliving matter makes living
• Disproved by Redi and Pasteur– New Idea:
• “biogenesis”…life comes from life
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Introduction to Evolution
• So, then where did the first cells come from?
– Early earth• Very hot; volcanoes; violent storms/lightning
– Miller & Urey experiment• Under early earth conditions, organic
compounds form & group together into “protocells”
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Introduction to Evolution• But, when did we actually get cells? And how?
– Evidence of first cells• 3.4 bln yrs ago• Most likely anaerobic bacteria (no O2 in air)
– First photosynthetic cells• 2.8 bln yrs ago• Increased O2 in atmosphere• Led to ozone layer that protects from UV rays =
more cells• Aerobic cells could now develop
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Darwin’s Idea
• How did Darwin form ideas about evolution?– Fossils showed organisms changed over time
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Darwin’s Idea
• How did Darwin form ideas about evolution?– Geologists showed that earth was very old
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Darwin’s Idea
• How did Darwin form ideas about evolution?– He saw diverse species (ex: finches on Galapagos
Islands, all with variations)
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Darwin’s Idea
• How did Darwin form ideas about evolution?– Malthus noticed populations grow faster than their
food supplies (they produce too many offspring)
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Darwin’s Ideas
• What did Darwin conclude about species?– He identified that
populations change due to “natural selection” (nature selects who goes on)
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Darwin’s Ideas• What did Darwin conclude about species?
– Four assumptions:
• Populations produce large #’s of offspring (more than can survive with given food)
• Individuals in population have variations• Certain variations are more useful (these will
survive better)• Over time, “good” genes prevail in the
population, while “bad” ones fade out
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Evidence for Evolution• What direct evidence supports this theory?
– Changes in populations over time• Ex: peppered moth
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Evidence for Evolution• What direct evidence supports this theory?
– Structural adaptations• Ex: mimicry; camouflage
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Evidence for Evolution• What direct evidence
supports this theory?– Physiological changes
• Ex: drug-resistant bacteria;
• Ex: pesticide-resistant insects
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Evidence for Evolution• Is there indirect evidence of evolution?
– Fossils• show changes through time
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Evidence for Evolution• Is there indirect evidence of evolution?
– Embryology• Early similarities may show relation
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Evidence for Evolution• Is there indirect evidence of evolution?
– Embryology• Early similarities may show relation
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Evidence for Evolution• Is there indirect evidence of evolution?
– Embryology
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Evidence for Evolution• Is there indirect evidence of evolution?
– Biochemistry• Similar chemicals in most life forms (DNA, ATP)• More similarities in code means closer
relationship
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Evidence for Evolution• Is there indirect evidence of evolution?
– Anatomy• Homologous structures
– Similar origin, but may now have different function– Shows common ancestry– Ex: bird wing, whale flipper, human arm
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Evidence for Evolution• Is there indirect evidence of evolution?
– Anatomy• Analogous structures
– Similar function, but very different structure– Shows separate development…not related– Ex: bird wing & butterfly wing
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Evidence for Evolution• Is there indirect evidence of evolution?
– Anatomy
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Evidence for Evolution• Is there indirect evidence of evolution?
– Anatomy• Vestigial structures
– A part that no longer serves a purpose– Ex: snake hip bones; human wisdom teeth
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Mechanisms of Evolution
• Can individuals evolve?– No!– Genes are genes…cannot alter them*– Only populations can evolve– Gene pool = sum of all genes in population
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Mechanisms of Evolution
• How do populations evolve?– Any factor that affects genes in gene pool may
disrupt equilibrium…leads to change (evolution)– Mutations may cause a shift – Smaller populations more affected…higher
chance to concentrate recessives– Organisms moving in/out cause changes– Large populations not as affected by these factors
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Mechanisms of Evolution
• How do species evolve?– Called “speciation” (same species can breed)– Geographic isolation
• keeps individuals apart so cannot interbreed…over time they develop different traits (Ex: finches on islands)
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Mechanisms of Evolution
• How do species evolve?– Called “speciation” (same species can breed)– Geographic isolation
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Mechanisms of Evolution• How do species evolve?
– Called “speciation” (same species can breed)– Reproductive isolation
• no longer capable of interbreeding (timing, parts, gametes differ,…)
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Mechanisms of Evolution
• How fast can species evolve?– Gradualism
• Species start up over long time with gradual changes (millions of years)
– Punctuated equilibrium• Speciation occurs in quick bursts with
equilibrium in between (~10,000 yrs or less)
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Mechanisms of Evolution
• How fast can species evolve?
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Mechanisms of Evolution• Does evolution show patterns?
– Divergent evolution• Ancestral species evolves into many species
that fit different habitats• Ex: finches; common on islands
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Mechanisms of Evolution• Does evolution show patterns?
– Convergent evolution• Distantly related organisms end up with similar
traits• Occurs when have similar habitats• Ex: cactus in S. American & African deserts
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Mechanisms of Evolution• Does evolution show patterns?
– Convergent evolution
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Modes of Selection
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Directional Selection
Pushes toward ONE extreme or the other
Ex: in dry years, beak size pushed to larger
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Diversifying Selection
Pushes toward both extremes
Ex: small beak for soft seeds; large beak for hard seeds; medium beak is bad at both types of seeds
so selected against
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Stabilizing Selection
• Pushes to average• Ex: cactus with few
spines eaten by animals more; cactus with too many spines invaded by more parasites
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The End
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Quiz – Evolutionfor use with Questions 1 & 2
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Quiz – Evolutionfor use with Questions 3-5
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Quiz – Evolutionfor use with Question 6
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Quiz – Evolutionfor use with Question 7