Evolution

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Evolution

• Ch 13

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Historical Theories

• Anaximander (2500 yrs ago)
• Aristotle
• Georges Buffon (1700s)
• Jean Baptist Lemark (late 1700s - early1800s)
• Erasmus Darwin

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Charles Darwin
1859
1874
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Voyage of the HMS Beagle
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On the Origin of Species

• Descent With Modification
• By means of Natural Selection

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How Did Darwin Come Up With His Ideas?

• Scientific Method
• Key observations
• Traits vary in a population
• Most traits are inherited from parent to
  offspring
• More offspring are produced than the environment
  can support (Thomas Malthus)

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Trait Variation
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Recap

• Limited resources
• Overproduction of offspring
• Heritable individual variation
• Therefore, survival depends partly on inherited
  features

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Darwins Theory of Evolution

• In a varied population, individuals whose
  inherited characters best adapt them to the
  environment are more likely to survive and
  reproduce.
• Therefore, more fit individuals tend to leave
  more offspring than less fit individuals.
• Natural Selection is the mechanism
• Reproduction (differential) is Key

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Natural Selection
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Artificial Selection
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Observing natural selection
0

• Camouflage adaptations that evolved in different
  environments

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Pestacide Resistance
0
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Antibiotic resistance
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• The excessive use of antibiotics is leading to
  the evolution of antibiotic-resistant bacteria

Colorized SEM 5,600?
Figure 13.13
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Natural Selection Experiment

• Darwin Finches (Galapagos Finches)
• Similar EXCEPT for beaks
• Beaks specialization

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Support for Descent with Modification

• Biogeography
• Fossil Record
• Molecular Biology, Biochemistry, Cell Biology
• Comparative Anatomy

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Biogeography
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• Geographic distribution of species
• Galápagos animals resembled species of the South
  American mainland more than animals on similar
  but distant islands
• Organisms may have common ancestor

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Fossil Evidence
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• Organisms evolved in a historical sequence

A Skull of Homoerectus
D Dinosaur tracks
B Petrified tree
C Ammonite casts
E Fossilized organicmatter of a leaf
G Ice Man
F Insect in amber
Figure 13.3AG
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Fossil Evidence
0

• Many fossils link early extinct species with
  species living today

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Comparative Anatomy
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• Comparison of body structures in different
  species
• Homology- similar characteristics resulting from
  common ancestry
• Homologous structures- features with different
  functions but structurally similar due to common
  ancestry

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Comparative Embryology
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• Comparison of early stages of development among
  different organisms

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Molecular Biology
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• Comparisons of DNA and amino acid sequences
  between different organisms to reveal
  evolutionary relationships

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Unit of Evolution
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• Evolution acts on individuals, affects whole
  populations
• Populations are the unit of evolution
• Group of individuals of the same species living
  in the same place at the same time

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Unit of Evolution

• Evolution is change in prevalence of heritable
  traits in population through time
• A gene pool
• Is the total collection of genes in a population
  at any one time
• Microevolution
• Is a change in the relative frequencies of
  alleles in a gene pool

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Hardy-Weinberg Equilibrium

• Frequency of alleles in a stable population will
  not change over time
• Very large population
• Population is isolated
• Mutations dont alter gene pool
• Random mating
• All individuals are equal in reproductive success
• In reality, this never happens

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Agents of Change

• Genetic Drift
• Bottle neck affect
• Founder affect
• Gene Flow
• Mutation
• Non Random Mating
• Natural Selection

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Variation
0

• Extensive in most populations
• Mutation and sexual recombination generate
  variation and can create new alleles.

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Endangered species often have reduced variation
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• Low genetic variability
• May reduce the capacity of endangered species to
  survive as humans continue to alter the
  environment

Figure 13.10
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Types of Selection
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Sexual Selection

• Sexual Dimorphism
• Sexual Selection- where individuals with certain
  characteristics are more likely to obtain mates
  than others.
• Intrasexual selection
• Intersexual selection

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Diploidy

• Balancing selection
• Heterozygote advantage
• Frequency-dependent selection
• Neutral Variation

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Natural Selection is Limited

• Only act on existing variation
• Historical constraints
• Compromise
• Chance, selection and the environment