Evolution N Darwinism - I didnt understand. Can anyone explain? (Sep/09/2007 )

I seriously didnt get this joke. Does it need knowledge of science, language or just sense of humour to understand this?

One day the zoo-keeper noticed that the orang-utan was reading two books: the Bible and Darwin's Origin of Species. Surprised, he asked the ape, "Why are you reading both those books?"

"Well," said the orang-utan, "I just wanted to know if I was my brother's keeper or my keeper's brother.

"Am I my brother's keeper?"

It's a memorable quote in the bible found in Genesis 4:9,
'And the Lord said unto Cain, where is Abel thy brother? And he said, I know not: Am I my brother's keeper?'

Cain sarcasm can be more readily perceived if we paraphrase it; Suppose a mother came home where she had left her two teen-age children working or playing. When she enters, she sees only one. She asks, "Where is your brother?" The remaining irreverent child might ask, "Am I a baby sitter?"

In a more general context, it is a parable. It ask if each person responsible and accountable for the actions and welfare of others. Cain's reply has come to symbolize people's unwillingness to accept responsibility for the welfare of their fellows

So in this joke, the Orangutan is asking if it is being held responsible for the damage/crimes that humanity has caused. (Yes, a very pro-evolution analysis.. alternatively said orangutan may well be asking if it was resposible for the actions of other orangutan.)

As for "Am I my keeper's brother?"
Said orangutan is asking if it was related to its zookeeper.

Brilliant and funny.

Thank U perneseblue.