When Darwin wrote the Origin of Species he couldn't have known about the huge advances that would come later. He was wrong on some points that creationists like to highlight. But, the reason we revere the genius of the man is that his insights were so often right. And so it has proven again in a new paper on the inner ears of sloths. I won't say anything more about it since Jerry Coyne has beaten me to the punch and written an extremely good and detailed account of the paper on his website Why Evolution is True.