Human Nature

The other day, in my Quest class once again, we were discussing the story of Adam and Eve. Some students proposed that it was a story of humans losing their innocence and bringing sin into the world. Some said that humans are naturally bad and have to work to be good while animals are naturally good, but none of the arguments seemed to nip it for me. I got myself to thinking. The heart of the matter seems to be that it is illustrating the difference between humans and animals. The snake doesn't seem to have a choice in the story, he simply plays a role. His role is to be the temptations. The human does have a choice. They can choose to either take the fruit or leave it. I think the largest difference here is that humans have choice while animals don't. Each animal is intrinsically good, or mean, or aggressive, or reclusive. Humans are not intrinsically anything. Anybody with me on this? Arguments for or against? Is what makes humans human having choice and the responsibility for our actions that result therefrom it?