What does adaptation have to do with homologous structures?

Homology is the occurrence of similar structures in different organisms because they are descended from a common ancestor by the process of evolution. The same structure can be adapted for different functions in different organisms, but still reveal the same underlying, homologous structure. So organs which appear to be very different in different organisms can in fact contain the same structures ie homologous structures. A famous example is the pentadactyl limb in vertebrates. This is adapted for many different forms of locomotion but still contains the same basic pattern of bones. For example, the human arm, bird wing, bat wing, whale flipper and horse leg are adapted for different functions but have the same internal structure ie a single upper limb bone, two lower limb bones, several wrist/ankle bones and hand/foot bones with five digits (fingers/toes). So, adaptation can lead to the modification of homologous structures in the descendents of a common ancestor. For more information see: http://www.zoology.ubc.ca/~bio336/Bio336/Lectures/Lecture5/Overheads.html http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_09 http://evolution.berkeley.edu/evolibrary/article/similarity_hs_01 http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Taxonomy.html