Convergent and Divergent Evolution

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Convergent and Divergent Evolution

• Notes on notes
• Listen to what I have to say first then copy it
  down.
• You dont have to write anything in red.

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Questions

1. What is Divergent evolution?
2. What is the evidence for divergent evolution?
3. What is convergent evolution?
4. What is the evidence for convergent evolution?

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Divergent evolution

• When species with a common ancestor evolve into
  very different forms. This is often what we
  imagine when we think about evolution.
• Evidence homologous structures structures that
  evolved from a common structure. May have the
  same components but different a function and or
  structure.

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Homologous limb bones
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Convergent Evolution

• When two very remotely related species develop
  very similar forms independently.
• Bits of anatomy that strongly resemble structures
  from another species are called analogous
  structures.
• Analogous structures tend to be superficially
  alike but constructed differently e.g. insect
  wings and bird wings.
• This is as opposed to homologous structures that
  are constructed from the same components but look
  different.

Remember all species are somewhat related
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The relationship between insect wings and bird
wings is analogous The relationship between
different bird wings is homologous
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Question Are these homologous or analogous?
Pterodactyl (a reptile) Bird Bat (a
mammal)
How is this for irony, the above picture is taken
from Harun Yahya http//www.harunyahya.com/refuted
10.php which is an anti-evolution website!
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The answer is both

• As forelimbs they are homologous as they evolved
  from the same components
• As flight structures they are analogous since
  they evolved independently to solve a similar
  problem.
• The line between analogous and homologous can be
  blurred. This is a reflections of the fact that
  every living thing is related if you go back far
  enough.

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Convergent Evolution
? Ichthyosaurus (a reptile)
Ichthyosaurus?
Swordfish (a fishduh) ?
Dolphin (a mammal)
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Why converge?

• To fill similar ecological niches and hence solve
  similar problems.
• Limited niches are available either fill the
  one available or become extinct
• Only a few engineering solutions are suitable
  to fill a niche.

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Discussion question

• Is evolution all about chance?
• How do analogous and homologous structures helps
  us answer this question?

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