History of ideas

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Evidence for Evolution Overview
Announcements

• History of ideas
• Direct observation of microevolution
• Vestigial structures
• Fossil record
• 1. Succession
• 2. Transitional forms
• Evidence of common ancestry
• Evolutionary trees
• Homology
• Radiometric dating

I will cover during lecture Review on your own
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History of ideas

• Pre-Evolution
• 400 BC Plato established the idea of essential
  nature.
• 350 BC Aristotle fixed properties of species.
• Through 1700 Christian thought Elaborated fixed
  essence Scala Naturae (natures ladder). Describe
  gods creation.
• Evolutionary ideas
• 1700-1850 C. Buffon, E. Darwin, J. Lamarck, R.
  Chambers, all propose some form of evolution.
• 1858 C. Darwin and A. Wallace, present paper on
  evolution by natural selection.
• The modern synthesis
• 1937 Dobzhansky integrates Mendelian genetics.
• 1940-present mopping up after the Darwinian
  elephant (J. Coyne).

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Direct observation of microevolution

• Soap bug Beaks pierce pod coat to reach fruit at
  center
• 1992 comparison of beak lengths.
• Flat-podded fruit introduced in 1920s.
• (Carrol and Boyd, 92)

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Direct observation of microevolution

• Museum specimens
• Biases?
• How many replicates?

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Experimental evolution

• Controlled manipulative experiment
• Replication

Many generations
Compare fitness
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Experimental evolution
Holland 01
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Vestigial structures

• Functionless or rudimentary version of a
  significant body part in similar, presumably
  closely related, species.
• Arrector pili useful in hairy mammals loft,
  defense.
• Pseudogenes non-coding versions of functional
  genes.
• 6-20 of human genes

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Vestigial structures

• The appendix in a rabbit (left), fetal human
  (middle) and adult human (right).

9
Succession

• The close relationship between fossil and extant
  species from the same geographical area and
  between fossils within adjacent rock strata.
• E.g., p. 43
• pygmy armadillo and fossil glypodont (Argentina)
• Wombats and extinct Diprotodon (Australia)

10
Transitional forms

• Archaeopteryx feathered dinosaur. An
  intermediate, but not necessarily an ancestor of
  birds.

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Transitional forms
Mammals terrestrial to aquatic

• Primarily aquatic
• Paddling hind limbs

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Transitional forms

• Mammals terrestrial to aquatic

Copulatory (grasping)
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Transitional forms
Mammals terrestrial to aquatic

• vestigial

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Evidence of common ancestry Evolutionary trees

• From On the origin of Species, 1859.
• A population or species
• Note extinctions and descent with modification.
• e.g. femur weight

15
Homology

• Possession of a trait in two or more species
  derived from their common ancestor.

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Homology?

• Fusiform body?
• What do their ancestors look like?
• Vertebrae?

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HomologyGenetic code

• Triplet of nucleotides coding for AA conserved
  across life.
• Why so pervasive?
• What happens to tRNA mutants in which UUU codes
  for serine?

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HomologyPseudogenes
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Pseudogenes

• Accumulate mutations at a constant rate.
• Mutation rates are measured independently across
  many genes in model organisms.
• We can measure the number of mutations based on
  sequence comparison to the functional parent
  gene.
• Therefore we can infer their age.
• Prediction of evolution from common ancestor
• older psuedogenes should be found in more species

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Homology

• Distribution should be proportional to age.

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Homology
independence (between estimated age and observed
distribution)

• Is the prediction met?
• Inconsistencies?
• AS not found in Gorilla yet younger alpha-Enolase
  is.
• What can you infer about relative ancestry?
• What is implicit in animal models used in
  biomedical research?

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Geologic scale
Relative age of rocks assessed, e.g., by
principle of superposition (young atop old).
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By 1850s measurements of geologic processes
indicated earth was at least millions of years
old, supporting evolutionary theory.
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Radiometric dating

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Radiometric dating

• Half-life is absolute and invariant

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Geologic scale

• Absolute age of rocks combined with geologic
  scale
• Earth 4 billion years
• Life 2.7-3.7 billion years

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Evidence of common ancestryEvolutionary trees
speciation

• Common ancestor
• sequence of events can be inferred.

Branch lengths arbitrary here.