Selection

• Mutations provide a continuous supply of genetic variation
• Natural selection occurs within competitive populations
• Genes provide the source of variaion, natural selection acts on individuals and their phenotypes
• Stabilizing Selection


  Once a species has become welll adapted, selection pressures will tend to prevent them from changing

  Natural selection eliminates extreme variations of a particular trait

  (Most common)
• Stabilizing selection


  It is favourable to have medium sized body, overtime, the size stays the same
• Directional selection


  Environment favours individuals with more extreme variations of a trait

  Observable change in a population especially in large populations with short generational times
• Directional selection


  Overtime, birds with larger beaks are favoured therefore the majority have large beaks

  
• Disruptive selection


  Favours individuals with variations at opposite extremes of a trait

  Significant evolutionary mechanism for the formation of distinctive forms within a population. This leads to speciation
• Disruptive selection


  Birds were transported to an isolated island, where it is favourable to have small beaks to eat seeds or large beaks to pick at bugs.

  
• Sexual Selection


  Favours the selection of any trait that influences the mating success of the individual.

  
  

  Females selection of males is based on: behavior, appearance, competition

  
  

  Can result in detrimental traits