ID includes everything from full-on Young Earth Creationism to Behe's idea of God as occasionally throwing a little genetic engineering into the evolutionary process and the front-loaded evolution described in this forum by Genomicus. Although it is fair to mention that the YECs seem more acceptable to the ID mainstream than the other views which appear to be no more than tolerated fringe elements in the ID movement.
I would say that mainstream ID (Old Earth Creationism) does not make such predictions but the fringe views in ID which include common descent do.
How do they justify this prediction, in your opinion?
Based on their belief in common descent.
I thought of another prediction that is often made: there will be biological systems such that their origin cannot be explained by naturalistic means. The reason it would make this prediction is that as a feature or process is brought into existence by the intervention of an intelligent agent the path of naturalistic process would come to an end at that intervention point.
I don't like confusing the natural/supernatural with natural/artificial, and it's a particular problem with ID. The mainstream do claim it as a prediction based on their supernaturalism. Behe, I think, still tries to claim it. I don't think that Genomicus does.
So I'd say that most ID supporters would agree and mean that a supernatural cause would be needed (although they might not say so) but some on the fringes might only mean that evolution involved some artifice, and some wouldn't agree at all.
I would suggest that the vagueness of ID is an intentional feature of the movement. ID was always intended as an alliance of anti-evolutionists, influencing the public to get their way, and to get around the First Amendment - if it were as obviously religious as the YEC "Creation Science" it would fail. Thus the official position has to be compatible with a wide range of views - including Young Earth Creationism - and to do so without being obviously religious.
The fact that this vagueness prevents ID from offering a real alternative to evolutionary theory is clearly acceptable to the ID movement. Clearly political considerations come before science or even honesty. For this reason I would suggest that anybody who is interested in scientifically investigating the possibility of "intelligent design" in life should choose a different label, rather than risk tainting themselves with association with the political ID movement.
Because saying that humans popped into existence for no reason seems pretty silly. So, if humans weren't intelligently designed there must be principles that allowed humans to come into existence.
See my answer to bluegenes.
Which seems to be no more than the naive argument that we should infer design from any sufficiently complex system - to be generous to it. It doesn't require much complexity to "operate according to principles". The orbits of the planets for instance - or even a single atom.
IN that case there would have had to be principles that have existed within the universe prior to human life, which then means that there would have to be principles that existed prior to the formation of the universe.
And that is a problem ? (Unless you assume an eternal universe or a universe that popped into existence for no reason it HAS to be true).
That doesn't tell us anything except that there are principles. It tells us nothing about why and how those principles exist.
In other words you value jumping to the conclusion that you want over honestly assessing the evidence. Those of us who are more interested in the truth than supporting your personal beliefs do not share that assessment. The fact is that you cannot rationally jump from "operating according to principles to "it was designed"
"All B are A" is not a good reason to even suspect that "All A are B".
Now unless you have a rational argument, for instance explaining how streams and rivers - and designers - could exist without underlying principles then you're just irrationally jumping to conclusions.