Evolution

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Evolution
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Charles Darwin

• Known as the Father of Evolution
• Wrote book On the Origin of Species
• Sailed the world on a ship called the Beagle

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Darwin
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Evidence for Evolution

• The fossil record show biodiversity, mass
  extinctions and episodic speciation
  
• Geographic Distribution of Living Species shows
  similarities among species living on different
  continents
  
• Homologous Body Structures structures that have
  different mature forms but come from the same
  embryonic tissue.
  
• Similarities in Early Development embryos of
  many vertebrates are very similar.
  

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Embryology
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Fossils and Evolution
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Natural Selection

• Over time natural selection results in changes in
  the inherited characteristics of a population.
  These changes increase a species fitness
  (ability to survive and reproduce) in its
  environment.
• Natural Selection causes struggles for existence
  and survival of the fittest.
  
• Natural Selection act on the phenotype rather
  than the genotype of a species.

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Gene Pools

• A gene pool is the combined genetic information
  of all the members of a particular population.
  
• A gene pool typically has two or more alleles for
  a given trait.
  
• Homozygous lethal traits can be carried by
  heterozygous individuals and thus remain in a
  gene pool.
  
• Relative Frequency is the number of times an
  allele occurs in a gene pool compared with the
  number of times other alleles occur.

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What are gene pools?
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Sources of Variation

• Two main sources are mutations and gene
  shuffling.
  
• Mutations changes in DNA sequence. These may
  or may not affect an organisms fitness.
  
• Gene shuffling is the random shuffling of genes
  caused by sexual reproduction.

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Natural Selection on Single-Gene Traits

• Natural selection on single-gene traits can lead
  to changes in allele frequencies and thus to
  evolution.
  
• If the change is beneficial to the organism, the
  change may cause the original form to fade out
  and the newer organisms to be more fit and take
  over.

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Natural Selection on Polygenic Traits

• Natural Selection can affect the distribution of
  phenotypes in a population in any of three ways
  directional, disruptive and stabilizing.

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Directional Selection

• Directional Selection Evolution causes an
  increase in the number of individuals with the
  trait at one end of the curve.
  

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Stabilizing Selection

• Individuals in the center of the curve and more
  fit and thus the curve narrows

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Disruptive Selection

• Individuals at the ends of the curve are more fit
  than the ones in the middle causing two curves to
  form and possible new species to form.

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Genetic Drift

• In small populations, individuals that carry a
  particular allele may leave more descendants than
  other individuals, just by chance. Over time, a
  series of chance occurrences of this type can
  cause an allele to become common in a population.

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Hardy-Weinberg

• Genetic equilibrium takes place when allele
  frequencies remain constant.
  
• In order for genetic equilibrium to take place,
  five factors must remain true.
  
• 1. random mating
• 2. Large Population
• 3. No movement in or out of the population
• 4. No Mutations
• 5. No Natural Selection

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Hardy-Weinberg
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H-W Conditions
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Speciation

• Reproductive Isolation occurs when members of two
  populations cannot interbreed. At that point,
  they have different gene pools.
  

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Types of Isolation

• Behavioral Isolation Two populations capable of
  interbreeding but have differences in courtship
  rituals or other types of behavior.
  
• Geographic Isolation Populations are separated
  by geographic barriers such as rivers, mountains,
  or bodies of water.
  
• Temporal Isolation Species reproduce at
  different times of the year.

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Speciation
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Galapagos Finches

• Speciation in the Galapagos Finches occurred by
  founding of new populations, geographic
  isolation, gene pool changes, reproductive
  isolation, and ecological competition.

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Survival

• Variation within a species help insure that some
  will survive major changes in the environment.
  
• Major diversity of species also insure that some
  of the species will survive major environmental
  changes.