Modifications of Body Plans

• Descent with modification.

  Provides evidence of evolution.
• Modification in Vertebrates

  • Forelimbs of various vertebrae 
  • look different and perform different functions, but show the same basic body plan. 
  • Functions can include digging, flying, running and swimming. 
• Basic body plans consist of

  • One proximal long bone(humerus)
  • Two distal bones (radius and ulna)
  • Wrist bones (carpals)
  • Five metacarpals that make up the palm 
  • Phalanges 
• Homologous Structures

  • Similar structures with the same body plan that perform different functions. 
  • Homologous structures provide evidence of evolution because the similarities may be tracked down to a common ancestor. 
  • The adaptations in the structure of the forelimbs develop independently in each group according to the organism’s habitat and mode of life. (aka evolution)
• Divergent Evolution

  Where organisms develop from a common ancestor, but follow different evolutionary paths.
• Analogous Structures

  Some body structures perform the same function in different organisms, but did not originate from a common ancestor. 
• Convergent Evolution

  Where organisms are not related, but develop structures for similar environments completely independently of each other
• Modification within a species

  • Many species changed over millions of years to form the species we know today
  • These modifications are modified descendants of earlier species. 
  • Modifications occurred to adapt to different environments.