Voyage of the Beagle

A friend and I are planning to read The Origin of Species in October. While she's on vacation I'm reading The Voyage of the Beagle describing Darwin's journey beginning in 1831. I noticed a few touchy references to blacks and slavery before I came to this in the second chapter.

It may be said there exists no limit to the blindness of interest and selfish habit. I may mention one very trifling anecdote which at the time struck me more forcibly than any story of cruelty. I was crossing a ferry with a negro, who was uncommonly stupid. In endeavouring to make him understand, I talked loud, and made signs, in doing which I passed my hand near his face. He, I suppose, thought I was in a passion, and was going to strike him; for instantly, with a frightened look and half-shut eyes, he dropped his hands. I shall never forget my feelings of surprise, disgust , and shame, at seeing a great powerful man afraid even to ward off a blow, directed, as he thought, at his face. This man had been trained to a degradation lower than the slavery of the most helpless animal.