Divergent Evolution

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Divergent Evolution
Divergent evolution is the accumulation of
differences that can lead to speciation.
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• Homologous structures
• similarities in structures due to common
  ancestry.

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Examples of Homologous Structures
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• Vestigial structure
• A structure that is reduced in function or
  structure, but may have had function in
  ancestor.
• Examples
• Appendix
• Tonsils
• Ostrich wings

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Star Nosed Mole Reduced sense of vision.
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• Convergent evolution
• Distantly related species evolve similar
  adaptations, because they occupy similar niches,
  have similar natural selection pressure.
• Example Anteater and aardvark

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In convergent evolution, trait is not shared by
more closely related species. The trait evolved
independently in more distantly related species
because the of similarities in natural selection
pressure.
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• Analogous structures
• similarities in structure on more distantly
  related species, due to convergent evolution.
• Example wings of butterflies and bats

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Applying the Concepts

• Snakes have skeletal remnants of legs. What
  term describes this type of structure?
• Vestigial structure

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Applying the Concepts

• Whales and other sea mammals have a similar
  shape to fish, even though they are more closely
  related to land mammals. What type of evolution
  is this an example of?
• Convergent evolution
• What term describes the relationship between
  fish and whale fins?
• Analogous structures

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Applying the Concepts

• The teeth of beavers and the tusks of elephant
  stem from a common ancestor, but they are adapted
  for different functions. What is this an example
  of?
• Homologous Structures

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Coevolution
A process in which two (or more) species
reciprocally affect each others evolution.
Changes in the gene pool of one population
resulting changes in the gene pool of the other
species.
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Coevolution can be a positive interaction,
resulting in a highly mutualistic
relationship. Example Specialist pollinators
that only pollinate one type of flower.
Advantage to pollinator- no competition for food
source. Advantage to plant- do not need to
produce as much pollen
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Coevolution can be an adaptation to a negative
effect of another species. An evolutionary arms
race Example Increasing levels of toxins in
one species to avoid predation, with the predator
developing increasing tolerance to the toxin.
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Fossils
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Relative DatingAge is determined in comparison
to another event.
Law of Superposition For sedimentary rock
layers, if undisturbed the youngest layers will
be on the top.
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Absolute Dating Radioisotope Dating
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Half-Life The amount of time that it takes half
of a radioactive sample to decay.
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Half-life Comparisons
Radioisotope Half-life
Berillyium-11 13.81 seconds
Iodine-131 8 days
Strontium-85 11 years
Tritium (Hydrogen-3) 12 years
Uranium-235 700 million years
Uranium-238 4.5 billion years
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Determining amount of radioactive isotope
remaining
Number of Half-lives Fraction Remaining Formula for Fraction Remaining
1 1/2 (1/2) 1
2 1/4 (1/2) 2
3 1/8 (1/2) 3
4 1/16 (1/2) 4

• Formula N No (1/2)t
• t number of half-lives
• N amount left No original amount

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Applying the Concepts

• Strontium-23 has a half-live of 11 years.
• If 1/16 of the original sample is left, how old
  is it?
• 44 years
• (1/16 is four half-lives)
• Carbon-14 has a half life of 5, 370 years. If a
  sample is 16,110 years old, what fraction of
  Carbon-14 would remain?
• 1/8th (3 half-lives)

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Evidence for Evolutionary Relationships

• Fossil Record
• Transitional Fossils
• Example Archaeopteryx is a transitional fossil
  between dinosaurs and birds.

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Evidence for Evolutionary Relationships Cont.

• Anatomical Comparisons
• However, anatomical comparisons can be
  misleading, because two species may have
  similarities due to convergent evolution rather
  than a common ancestor.

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Evidence for Evolutionary Relationships Cont.

• Biochemical Evidence
• DNA sequence (also known as genetic evidence)
• Protein sequence since each gene encodes a
  protein, changes in the gene will be reflected in
  changes in the amino acid sequence of the
  protein.

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Biochemical evidence is considered to be the most
reliable way to compare evolutionary relationships
among species.