Proper tense usage?

I'm writing a research paper that can or should take place in two tense, present and past. Do I HAVE TO keep the entire paper using only one tense, or would it be wrong if I use past and present tense for curtain paragraphs depending on the situation?

[Tdol]

You can use both tenses. If it is a scientific paper, the descriptions of experiments, etc, could be in the past, but the analysis of the results could be present if the results are facts.

My paper starts out describing the historical background of my topic, then gradually builds up to modern problem of that topic. It's just that I was once told to stick with one tense throughout an entire paper, and it's really difficult to do that on this paper, so since it's OK, I will try to stick to one tense per paragraph.

[mykwyner]

The general rule is that when writing about literature always use the present tense. Therefore, we say: Chaucer says the miller is foolish, not said and was. I don't see how this would be the least bit important in the type of paper you are writing. You could say, "America was once a rugged wilderness where animals roamed freely, but now is one enormous strip mall where animals hide from humans. Feel free to mix tenses to your little heart's content, just don't confuse the reader.