Descent with Modification: A Darwinian View of Life

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Chapter 22

• Descent with Modification A Darwinian View of
  Life

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• evolution processes that have transformed
  life on Earth from its earliest beginnings to its
  current diversity
• greatest underlying principle in biology
• 1859 Darwin published On the Origin of Species by
  Means of Natural Selection
• arguing that species evolved from ancestral
  forms by natural selection
• -revolutionized scientific thought, but
  contrasted sharply with views of the time

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Figure 22.18 Charles Darwin in 1859, the year
The Origin of Species was published
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Figure 22.0 Title page from The Origin of Species
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Figure 22.10 Camouflage as an example of
evolutionary adaptation
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• Linnaeus (early 1800s)
• father of taxonomy branch of biology
  concerned with naming and classifying diverse
  forms of life
• -developed binomial nomenclature 2 part
• naming system

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• Cuvier a paleontologist proponent of
  catastrophism Earths changes are due to
  catastrophic events used fossils to back up his
  claim
• Hutton Lyell geologists supported idea of
  catastrophic events, but changing of Earth
  gradually
• Lamarck believed acquired characteristics could
  be passed onto organisms (ex giraffe neck
  length)

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• Darwins voyage 1831 (HMS Beagle)
• -took him to Galapagos Islands where he
  developed the idea of adaptation to environment
• Wallace 1858 developed idea of natural
  selection independently from Darwin published
  manuscript (before Darwin, but his was not as
  thorough)

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Figure 22.5 The Voyage of HMS Beagle
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Darwins ideas

• descent with modification
• - unknown ancestral prototype (no idea of
  genetics)
• - variation of individuals made differential
  reproductive success
• - those best adapted (most fit) leave the most
  offspring (passing on their characteristics)

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Figure 22.9 A few of the color variations in a
population of Asian lady beetles
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• Malthus many organisms reproduce, few offspring
  survive
• 1930s Population genetics emphasizes
  extensive genetic variations within populations
  recognizes importance of quantitative inheritance
  
• (reconciliation of Mendelism Darwinism)
• 1940s neoDarwinism (modern synthesis)
• importance of populations, gradualism, modern
  genetics

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Natural selection

• -the idea that organisms with favorable traits
  are more likely to survive and reproduce

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Evidence for evolution

• Biogeography geographical distribution of a
  species ex endemic island species
• (Australia, Galapagos, Madagascar)
• Fossil record supports common descent
• ex Archeopteryx links birds, reptiles
• Taxonomy reflected branching genealogy

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Figure 22.4 Strata of sedimentary rock at the
Grand Canyon
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• 4) Comparative anatomy anatomical similarities
• ex homologous structures, vestigial organs
• Comparative embryology helps identify
  anatomical homology less apparent in adults
  reflects genetic similarity
• ex comparing embryos of different
  vertebrates
• 6) Molecular biology similarities in DNA
  sequences protein sequences supports common
  descent

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Figure 22.14 Homologous structures anatomical
signs of descent with modification
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Table 22.1 Molecular Data and the Evolutionary
Relationships of Vertebrates
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Chapter 23

• The Evolution of Populations

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• Population -a localized group of individuals
  belonging to the same species
• Species
• -a group of populations whose individuals have
  the potential to interbreed and produce fertile
  offspring in nature

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• Gene pool
• the total aggregate of genes in a population
  at any one time
• Hardy-Weinberg theorem
• - frequencies of alleles and genotypes in a
  population remain constant over time

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Hardy-Weinberg theorem

• For a population to be in Hardy-Weinberg
  equilibrium, these 5 conditions must be met
• 1) large population size
• 2) no migration or emigration
• 3) no net mutations
• 4) random mating
• 5) no natural selection

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Hardy-Weinberg equation

• p2 2pq q2 1

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Example

• 500 plants
• 480 red (320 RR, 160 Rr)
• 20 white (rr)
• diploid 1000 alleles
• R 800 (320 x 2 640 RR, 160 x 1 160 Rr)
  800/1000 .8 80
• r .2 20 R p, r q
• (.8)2 2(.8)(.2) (.2)2 1
• .64 .32 .04 1

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Figure 23.4 Genetic drift
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Figure 23.3b The Hardy-Weinberg theorem
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Figure 23.3a The Hardy-Weinberg theorem
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Microevolution

• -relative frequencies of alleles in a population
  change over a succession of generations within a
  gene pool

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Causes of Microevolution

• Genetic drift changes due to chance usu. in
  small populations
• -conditions which may reduce population size
• a) bottleneck effect population drastically
• reduced by disaster, killing unselectively
• ex cheetah population reduced in the
• ice age, then trophy hunted to near
• extinction
• b) founder effect genetic drift in a new
• colony for that species ex colonizing
  isolated
• island, lake, etc.

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Figure 23.5 The bottleneck effect an analogy
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Figure 23.5x Cheetahs, the bottleneck effect
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• Gene flow migration of fertile individuals
  between populations
• Mutation changes in DNA
• Nonrandom mating - may include
• selective breeding choosing mates that are
  close by (may lead to inbreeding extreme is
  self-fertilization) or assortative mating
  individuals select partners like themselves in
  phenotype

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Figure 23.16x1 Sexual selection and the
evolution of male appearance
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• Natural selection (variation is at the core)
• polymorphism when 2 or more distinct forms
• are present in a population ex M F lions
  (sexual dimorphism) may be balanced (remains set
  in population)

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Figure 23.16x2 Male peacock
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Figure 23x2 Polymorphism
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• geographical variation genetic differences in
  population of a species varies regionally
• ex cline graded change along geographic
• axis
• recombination mutation add variety

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Figure 23.8 Clinal variation in a plant
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Variation may be preserved through

• diploidy hides recessive alleles
• balanced polymorphism heterozygote
• advantage ex sickle cell anemia
• Aa resistant to malaria
• AA susceptible to malaria
• aa sickle cell anemia

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Figure 23.14 Diversifying selection in a finch
population
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Figure 23.12x Normal and sickled cells
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Figure 23.10 Mapping malaria and the sickle-cell
allele
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• Fitness relative contribution an individual
• makes to the gene pool of the next
• generation
• Relative fitness contribution of a genotype to
• the next generation compared to the
• contributions of alternative genotypes
• for the same locus

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Modes of Natural Selection

• Stabilizing selection favors the mean
• Directional selection favors one extreme
  phenotype over another
• Diversifying selection favors both ends of the
  spectrum, not the mean
• natural selection acts on individuals, but
  populations evolve

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Figure 23.12 Modes of selection