Mechanisms of Evolution

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Mechanisms of Evolution

• Headings
• Vocabulary
• Important Info

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What is Going On?
The tree is getting larger. Did the tree evolve?
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Can Individuals Evolve?

• Individuals CANNOT change their genes and evolve!
• Populations, not individuals, evolve
• Unfit individuals may not survive and reproduce
  (pass on their genes)
• Natural selection acts on the gene pool all
  the genes in the population

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Changes in Genes Lead to Evolution

• 1. Mutations caused by environmental factors or
  by chance
• If the change is beneficial, becomes part of the
  gene pool
• 2. Genetic Drift random events affect numbers
  of genes in pool
• Weather natural disaster
• 3. Gene Flow individuals leave a population

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Small vs. Large Gene Pools

• All these changes affect small populations much
  more than larger ones

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Natural Selection Acts on Differences in
Populations

• There are 3 types of natural selection patterns

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1. Stabilizing Selection

• Average individuals in the population have the
  advantage
• Reduces differences within the population
  (become more alike)

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2. Directional Selection

• Favors one of the two extremes of a trait
• Ex Long beaks are advantage for woodpeckers.
  Eventually, beaks will become longer in the
  population.

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3. Disruptive Selection

• Favors those with either extreme of a trait
• The middle of the road individuals will
  eventually be eliminated from the population

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Evolution of a New Species

• This is called speciation
• Populations can no longer interbreed and produce
  fertile offspring

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Cladograms How to Read and Interpret
This cladogram shows a relationship between 4
species. They share a common ancestor at the root
of the tree. Note that this cladogram is also
a timeline. The oldest organism is at the bottom
of the tree. The four species at the top of the
tree are DIFFERENT species. Making new species is
called SPECIATION.
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Branches on the tree represent SPECIATION
the formation of a new species. The event that
causes the speciation is shown as the fork of the
V.
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Species B and C each have unique
characteristics. They also share a common
ancestor with Species A.
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A clade is a group of organisms that come from a
common ancestor.If you cut a branch off the
tree, you have all the organisms that make up a
clade.
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Consider this cladogram

• Q Which species is the oldest?
• A Sharks
• Q Which 2 species most recently shared a common
  ancestor?
• A Crocodiles and dinosaurs/birds
• Q Primates and rodents share what unique
  characteristic?
• A Hair