Homology

• Homology : similarity due to common ancestry
• Homologous Structures


  Example: mammlian forelimbs

  • compare human, cat, whale, and bat forelimbs, the pattern of bones, muscles, and even nerves are the same
  • these structures are homologous bc basic structures was originally inherited from CA (common ancestor)
• Embryonic Development

  • similarities in early development between spp
  • ex: all vertebrae embryos at one point during embryonic development have tail behind anus
• Vestigial Organs

  • nonfunctional organs NOW
  • ex: whales + pythons have hind limb bones which neither need. why do they have them?
  • ex: flightless birds with wing bones
  • ex: humans have ear moving muscles
  • even though these organs are nonfunctional rn, they evolved from CA where it WAS at one point functional
  • rn it doesn't cost anything to keep them
• Molecular homology

  • genetic code : universal
  • seen in homologous genes which were inherited from distant CA
  • ex: humans + bacteria in ribosomal subunits with identical functions (proteins)
• Homologies and "Tree Thinking"

  • when did homology evolve?
  • deep ancestral past needs to be uncovered, many shared components
  • more recent, less sharing of characteristics
  • use homologous characteristics to diagram evolutionary relationship through an evolution tree (phylogeny)