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Organisms are all related genetically according to the theory of evolution (common descent). Since all organisms are descended from a common ancestor, they must share the same basic genetic material. This is predicted by evolution. ID would certainly not have such a requirement. By ID I am referring to the notion that an intelligent designer actually did intervene in the development of the variety of species seen on earth. From discussing this with you, I get the feeling that we really agree on the issue of evolution, ie that evolution actually is the mechanism for the change observed in organisms. I also agree with you that it is possible that some intelligence did in fact direct this process. Where I believe we disagree is in whether this is a scientific theory or not. I don't think that there is any observation that would cause a reasonable person to say "since I observed this, there's no way that an intelligent being could ever have intervened in the process of the development of life." That's why I asked you to provide me with such an observation. It doesn't have to be something that has actually been observed. (Such as my example of an organism with something other than nucleic acids as its genetic material which has never been observed.) If there's no way to show that an idea is false, it is not science.

"Organisms are all related genetically according to the theory of evolution"

There's a problem right there - the earliest life forms didn't have DNA. The rest of the argument falls apart right there.

"Since all organisms are descended from a common ancestor, they must share the same basic genetic material."

That precludes several possibilities. One, it discounts genetic mutation, which could change significant parts of that original bit of code. Two, it precludes the possibility of multiple lifeforms forming independently from the basic compounds and amino acids we've seen form spontaneously in labs using early-Earth simulated conditions. Thirdly, it ignores the fact that, the other two things aside, the snippet of genetic material would likely be so small and insignificant that it could very well exist among all current living things yet remain virtually undetectable. The problem is that, as the complexity of the genetic makeup of organisms has increased, this common bit of genetic code could become spread out in such a way that it's nearly impossible to distinguish it from code added later. There may be a sequence of ABCDEFG in the original ancestor, but if ABC is in the middle of chromosome 6, DE is at the end of chromosome 19, and FG is at the beginning of chromosome 21, then it becomes pretty tough to look for that commonality.

"I also agree with you that it is possible that some intelligence did in fact direct this process. Where I believe we disagree is in whether this is a scientific theory or not."

Unless the 'intelligence' is an alien being, any speculation on that subject would delve into metaphysics, and would be beyond the realms of good science.

"(Such as my example of an organism with something other than nucleic acids as its genetic material which has never been observed.)"

Prions, though not classified as 'alive' by our ridiculous current standards (which also leave out viruses, calling them non-living), certainly fit this profile. 'Mad cow disease' is caused by a prion. Prions are merely proteins and contain no nucleic acids (so far as I know). I would also point out that, at some point in Earth's history, a gradual shift began toward what we have today - eukaryotes. Prior to that shift, life (or all we've seen of it) existed as prokaryotes. If you continue to take this trend backward in time, the only question is, do you reach a point where no nucleic acids were necessary, and could those types of life forms give rise to offspring which eventually would require nucleric acids? It's an interesting question, and one which I think the science is still too young to answer very well. Give it some time and I think a lot of these blanks will be filled in as the science and the methods improve.

It says nothing about the presence of designers in the process, however: and we know from human experience that designers can and do influence how species change. Note, however, that you're simply assuming that common descent is an absolute fact. It may in fact be true (or not) -- but unless you want to theorize that there's only one possible way for life to come about, common descent is not a biological requirement.

ID would certainly not have such a requirement.

Neither does evolution require such a thing -- it could have just turned out that way. Anyway, common descent is still not an argument against design. Perhaps it's a poor analogy, but pretty much all of my very numerous C++ programs originated from the first "hello world" program I wrote 15+ years ago. Why? Because it's easier to modify what I've already done, than to start from scratch every time.

Where I believe we disagree is in whether this is a scientific theory or not.

Well, given that we both agree that intelligent designers not only can, but quite often do intervene in the development of species, I fail to see why it is "scientific" to simply exclude the possibility when the topic turns to evolution.

It doesn't have to be something that has actually been observed. (Such as my example of an organism with something other than nucleic acids as its genetic material which has never been observed.) If there's no way to show that an idea is false, it is not science.

The only "false" idea in your previous example would have been that DNA is the only way to pass genetic information. However, it is pointless to provide "falsifiable tests" for things we already know to be true -- such as the fact that intelligent designers have influenced the development on species on Earth.