Passing by the primate area one day, a zoo attendant happens to notice a chimpanzee sitting on a rock with an open book in either hand, looking first at one and then at the other.

Upon closer examination, he identifies the books: the Bible and Darwin's Origin of Species.

Curious, he asks the chimp, "What's with the books?"

The chimp replies, "I'm trying to decide whether I'm my brother's keeper or my keeper's brother."