It's quite clear that he is saying the negroes and aboriginals lie between whites and apes on the evolutionary scale; not to mention he uses the word exterminate in regards to those people groups, the man was a monster just like Hitler when he tried to exterminate the Jews which he justified with the same reasoning as Darwin.
Saying that it would almost certainly happen is not the same thing as advocating it actually happening. Obama will almost certainly win the presidency at this point. Saying that doesn't mean I want him to! Besides, I really think you need to take Darwin's life into account as a whole. He didn't believe in social injustice, and he strongly opposed slavery.
Yes, he was a Victorian, a man of his time, and held certain supremacist ideas. However, he was not so hateful as to advocate genocide in the way you accuse him of.