Theory of Evolution by Natural Selection

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Theory of Evolution by Natural Selection
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Speciation and Homology

• Speciation produces sister species descended
  from a common ancestor
• Descendant species retain characters of common
  ancestor possibly in modified form.
• descent with modification
• modified character HOMOLOGY

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Evidence for common ancestry (genealogical
relationship)

• Same character in 2 or more species inherited
  from a common ancestor HOMOLOGY
• possibly modified since split from sister species
• The common ancestor no longer exists, so how can
  we tell whats a HOMOLOGY and whats not?

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Criteria for HOMOLOGY (Operational definition)

• 1. Position in relation to other body
  structures.
• 2. Embryonic origin
• 3. Continuity -- Characters homologous to
  another character are homologous to each other.

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Criteria for HOMOLOGY

• 1. Position in relation to other body
  structures.
• tetrapod forelimbs
• humerus
• radius ulna
• carpals
• metacarpals
• phalanges

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Criteria for HOMOLOGY

• 1. Position in relation to other body
  structures.
• insect wings, legs
• antennae

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Criteria for HOMOLOGY

• 1. Position in relation to other body
  structures.
• flower parts
• sepals
• petals
• stamens
• carpel (s)

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Criteria for HOMOLOGY

• 2. Embryonic origin similar developmental
  origin.
• 1st pharyngeal arch ? jaw
• limb buds
• lobes of brain
• heart

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Criteria for HOMOLOGY

• 3. Continuity -- Characters homologous to
  another character are homologous to each other.
• hyomandibular ? stapes (stirrup)
• quadrate ? incus (anvil)
• articular ? malleus (hammer)

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Ways HOMOLOGY provides evidence for evolution.

• 1. Comparative Anatomy
• 2. Comparative Embryology
• 3. Comparative Fossil Anatomy
• 4. Comparative Physiology Biochemistry

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Comparative Anatomy

• Modification of existing characters/organs for
  OTHER FUNCTIONS
• Forelimbs ? wings in birds,
• Forelimbs ? whale flippers
• 1st gill arch ? vertebrate jaw

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Comparative Anatomy

• Modification of existing characters/organs for
  OTHER FUNCTIONS
• Teeth ? fangs in rattlesnake
• Salivary gland ? venom gland

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Comparative Anatomy

• "Imperfection" of adaptation
• Panda's "thumb"
• actually radial sesamoid bone
• Human backbone
• "Oh, my aching . . ."
• after 2-3 million years, we are still subject to
  back strain

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Comparative Anatomy

• Modification for NO function
• Vestigial organs "Senseless signs of History"
• Characters that make no sense in present, but
  were used needed in ancestors

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Comparative Anatomy

• Modification for NO function
• Vestigial organs
• Pelvic rudiments of whales

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Comparative Anatomy

• Modification for NO function
• Vestigial organs
• Limb bones claws of boas, pythons
• Human coccyx

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Comparative Embryology

• Some traits seen only in embryos or larvae.
• HOMOLOGY with larval or adult traits in other
  organisms.
• Notochord in vertebrates.
• Notochord dorsal nerve cord in tunicate larvae.
• Bilateral symmetry in echinoderm larvae

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Comparative Fossil Anatomy The Fossil Record

• HOMOLOGY relates fossils to existing organisms
• Change in lineages
• Extinction
• Example
• fossil horses

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Comparative Fossil Anatomy The Fossil Record

• HOMOLOGY relates fossils to existing organisms
• Change in lineages
• Extinction
• Examples
• trilobites

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COMPARATIVE Physiology Biochemistry

• HOMOLOGY applies to physiological metabolic
  processes
• Glycolysis and Krebs cycle
• Mechanisms of cell signaling
• HOMOLOGY applies to biochemicals
• DNA as genetic code
• RNA to translate code into protein structure
• ATP as energy currency of cells

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Convergence

• Evolution (adaptation) of dissimilar organisms to
  common function, superficially similar
  characters.
• piercing sucking mouth in bugs, mosquitoes,
  fleas, butterflies
• "wings" in bird, bat, pterosaur, insect,
  (airplane ??)
• Convergent character NOT present in common
  ancestor!!

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Biogeography

• Geographic distributions of species, genera,
  families, etc.
• Organisms have evolved independently in different
  parts of the world.

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Biogeography

• Organisms have evolved independently in different
  parts of the world.
• Endemic species, genera, etc. on islands.
• Hawaiian honeycreepers
• Galapagos finches

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Biogeography

• Organisms have evolved independently in different
  parts of the world.
• Continents as big islands
• "Patagonian hare" in S. America
• Convergence of placental and marsupial mammals
• Australia
• marsupial "wolf," badger (T. devil), mole,
  mouse, deer (kangaroo),
• South America
• marsupial "horse," "saber-tooth predator

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Biogeography

• Used with fossil record to reconstruct
  evolutionary history.
• Camels in Asia camel, dromedary
• in S. America llama, alpaca
• Camels predicted in N. America fossils

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Biogeography

• Used with fossil record to reconstruct
  evolutionary history.
• Alligator in SE USA and China/SE Asia,
• Hellbenders in SE USA and China,
• Cyclocosmia in SE USA and Malaysia

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Biogeography

• Used with fossil record to reconstruct
  evolutionary history.
• Isthmus of Panama divided Caribbean from Pacific
  about 3 MYA
• several species crabs, snails, fish, etc. have
  nearest relatives on other side of land barrier.