Not quite, Mullet. Firstly, I think your philosophy text deserves some criticism. Strictly speaking the classic fallacies of reasoning occur when one attempts to establish the
truth of a proposition by an invalid argumnet. For example:
Either we have a soul or we do not.
You cannot prove we do not;
therefore we do.
This is a better statement of the form of the argument to ignorance than that given in your quote. Things get a little muddled when we talk in terms of "I am justified in believing it is true." Consider the ad hominem argument.
Either E=mc^2 or it does not.
Roger Penrose says E=mc^2;
therefore it does.
This is a fallacy because Roger Penrose's utterances do not affect the values of physical constants. However "Roger Penrose says E=mc^2; therefore I am justified in believing it does" is not, strictly speaking, a fallacy or an ad hominem argument because it can be fleshed out to a valid argument so long as the justification is included as one of the premises ...
I am justified in believing the statements of experts in their fields.
The statement "E=mc^2 is true" is a statement in the field of relativity.
Roger Penrose is an expert in the field of relavity ... etc etc... (you can do the rest, I presume)
The reason the justification must be included as a premise, is becuase a logical argument is only guaranteed to provide true conclusions following from true premises. It may not be true that I am justified in believing experts, or it may not be true that Roger Penrose is such an expert, or it may not be true that E-mc^2 is a statement in relativity, but in these cases I would err in my premises and not in my logic.
Now if you take Percy's and edge's statements you will see that they are both establishing
empirical criteria rather than criteria of strict logical deduction. They must do so because, as Percy points out, science
cannot prove anything in the formal sense of logical or mathematical proof. Indeed, if you are studying Philosophy, you have already, or will soon, come across the "riddles of induction" which show exactly why this is so. In this regard, note that edge places "scientific fact" in quotes to point out that there is a particular nuance to his usage of the term - to distinguish it from a more absolute form of proven truth such as may be found in mathematics or formal logic.
Percy and edge are not saying "evolution is true because it has not been disproved" but "science is justified in empirically regarding evolution as true because it has not been disproved." If you consider this in the light of the clarification I made to the argument from ignorance you will understand the difference.
edge also introduces another important distinction - namely that this empirical acceptance of evolution requires a
process of disproval or approval. For example, I could come up with a theory right now that the crab nebula is formed from the droppings of a giant space goat - could I regard this empirically true until disproven? I would be seriously mistaken if I did. The establishment of empirical truth is a process - a process which we call "Science."
So what was your mistake? You will be glad to know that it is a recognizable logical fallacy that you can avoid in the future: the fallacy of weak analogy. You are in effect saying
Science is like formal logic.
In Formal Logic, edge's statement would be untrue;
therefore edg'es statement is untrue.
But, as Percy and edge both tried to point in their own ways, Science is not like Formal Logic.
You may be tempted, as many a creationist before you, to say that therefore you are justified in doubting the conclusions of science. But, as a student of philosophy, you should be able to see through that one by recasting the argument to ignorance in empirical rather than formal terms.
Have fun philosophizing.