Creationists (and I include "Intelligent Design" advocates) observe all the diverse wonders of the natural world, and say "This is all so complex and wonderful, it can't possibly be due to random chance, therefore a god or a designer must have made it." Plus, we've got a book where it says that that is actually what happened. Problem solved! Science is pointless.
The assumption behind this belief is that any extremely complex "product" must have a more intelligent (and/or more complex) designer than the product itself. This fits in with our human perspective of the world around us. Jumbo jets don't come into existence on their own, do they? No, they have been designed by clever humans.
If you accept that complex products - living things for example - must always have a more complex designer, the immediate problem which arises is that the designer-god which made the Universe must therefore have a more intelligent or complex designer than itself. A "supergod" is needed to design the original god.
So this line of reasoning leads to an infinite regress of gods, each one more complex than the one which it designed, and so on. That can't be right, surely? Even creationists don't believe that.
So, er, what's the answer?
Edited by Blzebub, : typo