My Year of Darwin 5/12/2014:

"My dear Henslow: this is the last letter, which I shall ever write to you from the shores of America - and for this reason I shall send it.- In a few days time the Beagle will sail for the Galapagos Island. - I look forward with joy and interest to this, both as being somewhat nearer to England, & for the sake of having a good look at an active Volcano." Charles Darwin, Letter to Henslow July 1835 

I think everyone understands the importance of the Galapagos Islands to Darwin's thinking. He just spent a few weeks exploring the southwest coast of South America and has spent considerable time being thirsty, hot, or freezing cold. He was also sick for two weeks and kept the Beagle on shore while he recovered. Captain Fitzroy also considered resigning an account of his mental stability.  Adios South America.