Mole Palace and Cathedral, Rio De Janeiro'. Copperplate engraving by A. Kurle and T. Hair published Colburn 1838. Vol 1 of \The Narrative of the Surveying Voyages of the Adventure and Beagle\" by P.P. King (1839). Slaves and sailors interacting. Darwin visited Rio De Janeiro in April 1832. He was amazed by the tropical forest but also appalled by the slavery. A particular instances of a slave rowing a boat who cowered when Darwin held up his hand caused him to write \"I shall never forget my feelings of surprise, disgust, and shame, at seeing a great powerful man afraid even to ward off a blow\". \"This man had been trained to a degradation lower than the most helpless animal\". Adrian Desmond and James Moore (2009) have made the case that Darwin's interest in the common descent of man was tied to his belief that this understanding would foster humanitarian treatment of all men as brothers."