Have scientists figured out...

Hi. I have a question about the giant tortoises of the Galapagos Islands. I know that every island has a giant tortoise with a different shell shape. The reason for this is because the tortoises evolved to adapt to their habitat. I want to know if scientists have figured out what specifically causes the differences in the shells of the tortoises of each island. And if they did figure it out, what specifically caused the tortoises to evolve in the way they did?

Thanks,
Daniel pd.1

Dan, if I understand your question correctly about "what specifically causes the differences...", it is an adaptation to the vegetation of each island. For example, the tortoises with a raised front shell and long neck can feed on higher growing vegetation. Tortoises that feed on grasses or low growing vegetation will have dome-shaped shells. It is evolution at its finest. There is some interesting information about tortoises and the evolution of their shells at http://www.gct.org/tortoise.html. Check it out.