As I stated before, there is a danger of confusing the terms "evidence" and "inference." The evidence is always testable. The inference is not always testable. I gave the example of the universal common ancestor. This entity, if it existed, presumably has decayed. It is, to us, invisible, just like God, and therefore is believed in on the basis of evidence. It requires faith. And because we cannot travel back in time, the common ancestor theory is not fully falsifiable. True, you might be able to falsify it in certain ways - heck, if we master time travel, we might be able to falsify even creationism - but there seems to be a point of impasse beyond which we cannot falsify it due to our inability to go back in time. That is to say, if the DNA points to a common ancestor, this would be consistent with both a creationary and and evolutionistic model, as I argued earlier. As to which model one chooses will partly be based on evidence, partly on faith, because we cannot APODICTICALLY falsify either model.
As another example, take the Big Bang theory. Here is the same problem. The evidence is testable. The inference itself is not because no one presently, as far as I can see, exists in that time frame to watch what happened. So one's conclusion as to whether our origin begins with a Big Bang, or with God, or with some other theory, will be partly based on evidence, partly on faith, because our origin is currently invisible to us, just like God. It cannot be APODICTICALLY falsified.
As a third example, take physics itself. There is more than one possible model to explain the movement of bodies. The most popular models of the past century have resulted in some rather bizarre conclusions (warpage of space and time, time that slows down, wave-particle duality of light, relativity of simultaneity, particles with no definite location, etc. etc. etc.). I question some of the assumptions that have led to these conclusions. What has happened, as far as I can tell, is this. We began with an incorrect assumption or two. This led to the possibilities of discrepancies with observed data. To reconcile the discrepancies, we factor in accomodations such as "curvature of space and time" and "relativity of simultaneity" and so forth. The discrepancies are now resolved. We now predict reality perfectly. And in this sense we probably cannot APODICTICALLY falsify these theories. In fact scientists admit that no theory is really "proven." Since we always view reality through spectacles tinted with assumptions, "the truth" ultimately is to us invisible, just like God. But I hope that some physicisist will produce a better model that eradicates the bizarre conclusions currently accepted.
A fourth example, raised earlier, is the idea that other intelligent life exists on distant planets. If this life is smarter than we are it may hide itself from us such that we cannot falsify their existence. But if we see evidence of their existence, it would be a reasonable, scientific conclusion to infer it.
These examples indicate to me that falsifiability is ultimately an unrealistic goal. It is, in many cases, simply asking too much. As I said, the evidence is always somewhat testable and somewhat falsifiable. The INFERENCES such as modern physics itself, are not always testable/falsifiable in the full sense, in the apodictic sense, often because we cannot travel back in time, or often because our spectacles are tinted with preconceived assumptions, or because our instruments are insufficiently advanced to do all the necessary testing.
On this basis I conclude that falsifiability is not the ultimate critierion of a good scientific theory. What, then, is that critierion? I like the word forensics. A theory is scientific when the forensic evidence presented to our senses (both directly and via our instruments) points to a possible inference. Newton considered gravity forensic evidence that God exists. And when I look back at the above four examples, I feel satisfied that this definition of science fits all the possible scenarios much better than the falsifiability-notion.
There you have it. That's my opinion. These are my final comments on this particular issue. I don't want to spend more time on this issue, so I will let others have the last word.