What is a Transitional Form?
  Suppose that we have the following two creatures, one of which is the ancestor of the other:  
 
Ancestor
Descendent
  
 
 
  How would evolution work to create the descendent?      
 
possibility 1: gradual change from one to the other would produce these intermediates:

80% ancestor,

20% descendent

  
 
 

60% ancestor,

40% descendent

  
 

 

40% ancestor,

60% descendent

  
 

20% ancestor,

80% descendent

  
 
According to this model, every characteristic of the animal changes in parallel. This is what we predict only if individual animals change from one form to another form. But, genetics doesn't work this way.
  
 

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go directly to possibility 2: a series of mutations over many generations