I' Speciation:

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I. Speciation

• A type of divergent evolution that involves the
  formation of changes in the genes. This may
  eventually lead to the development of a new
  species if these accumulated changes provide and
  advantage of some sort. Speciation tends to
  occur when organisms become ecologically or
  geographically isolated.

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• A. Species A group of potentially interbreeding
  individuals that can produce fertile offspring
  because they share common gene pools. This leads
  to common anatomy, physiology, and behaviors.
  The species rule does not apply to all things.

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• Exceptions to this rule include
• a. the ability of clearly separate species to
  interbreed
• Dogs and Wolves
• Lions and Tigers
• Zebras and Horses
• (indicates recent divergence)

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• b. Some species reproduce asexually so there is
  no interbreeding
• c. Fossils cannot be classified this way b/c it
  is impossible to know what they were capable
  of
• d. The evolution of sub-species that may be able
  to interbreed but do not.

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B. Origin and Types

• isolation usually begins as geographic in nature
  due to migrations, this allows 2 gene pools to
  evolve independently of one another and become
  less alike.
• Speciation can happen
• a. very quickly (punctuated equilibrium) this
  is when small

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• changes accumulate rapidly possibly due to
  environmental change (volcanic eruptions). The
  process of rapid natural selection is followed by
  a period of stability. This is supported by the
  fossil record.
• b. Gradually- slow, continuous change over a long
  period of time

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C. Models of Speciation

• 1.Allopatric speciation that occurs between 2
  isolated populations separated by a physical
  barrier such as a dam or valley.
• Ex antelope squirrels are separated by the
  grand canyon and have evolved independently

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• 2. Sympatric speciation that occurs even without
  physical barriers in place. Animals make contact
  but are reproductively isolated
• 3. Parapatric populations evolve while
  maintaining separate territories that may in
  places overlap. There is some interbreeding in
  the overlap zone that leads to hybridization

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D. Reproductive Isolating Mechanisms

• Changes in a population that prevent cross
  species breeding.
• Behavioral differences in courtship rituals
• Ex. Fireflies each produce a different
  combination of light flashes

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• 2.Temporal becoming reproductively active at
  different times of the day, year
• Ex. Western skunk active in the fall, Eastern
  skunk active in the winter
• 3. Mechanical Anatomical differences prevent
  copulation

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• 4. Gamete Mortality offspring fail to develop
  after copulation because gametes are different on
  a chromosomal level
• Ex. Humans and chimps have different chromosome
  s (46 and 48 Respectively)