I'm not sure. I've always heard the terms rain-forest and jungle used interchangeably. True, jungles are usually thought of as impenetrable. Jungle implies tangled and unmanaged, because jungles ARE tangled and unmanaged. If there were no difference, we wouldn't need another word. As I attempt to recall conversations I've had with people who have been to jungles, the distinquishing factors have been 1) it's a lot darker throughout much more of a jungle, 2) it is more difficult to travel than through a mere woods. Although even in mere forests there are thickets and brambles and stands and other obstructions which are generally trivial to circum-navigate.
I say 'always' above, but the term rain-forest has only come to my attention in the last 25 years or so. Somewhere in that time-span it just became more common to hear "Amazon rain-forest" instead of "Amazon jungle," for example. There may be a slight difference in usage - rain-forest tends to be used when talking about the object in theoretical terms, whereas jungle seems to be more commonly used when the speaker is talking about actually going into or having gone into it. I'm not sure. Haven't really thought too much about it except to try to decipher those conversations of years ago.
It worked for Upton Sinclair because Jungles are places where the laws of modern, human civilization have not applied until recently. I don't think what's happening is that we use words like jungle to describe places where we are trying to justify our involvement. Or, if it does happen, it's completely ancilary to the fact that those places really are jungles.
Jungles do tend to be uncharted - by westerners - or anyone. It's one thing to have a verbal "map," mosaicked from various personal recollections - quite another to have a consistent, persistent, piece of paper that anyone can use. Of course, such a highfalutin thing as a map is more trouble than it's worth to the indigenous people, same as it would be for one of us when we're walking from our house to our local market. But if we go past the areas with which we are commonly familiar, maps tend to be very, very handy - and far easier to use, and far, far more reliable than verbal descriptions. (For those of us who can read them. My wife can't and that's why my daughters are navigators when we travel.)
I wonder now - did the early western explorer/conquerors refer to wooded areas in the temperate zone as jungles as a way of justifying intrusion?
k
