He likes to have many layers to his story, often paralleling the main story, and I'm sure I will pick up more little things on subsequent viewings when it comes out on DVD. Aronofsky's stuff is not what I would call mainstream for sure. There were a lot of points being made about life and death and how we [humans] typically percieve them and deal with them as well as the futility of the quest for "immortality". The number of layers makes this movie hard to describe, but from what I've seen, few directors capture human nature as well as he does. It is like looking directly into someone's dreams - disjointed, but still telling a story; you understand what happened, but what does it all mean?
What was discovered with the monkey could ultimately benefit all of mankind, so no, the monkey wasn't the only one...