The problem is, the DNA evidence just shows that all life on earth is related. It doesn't require descent from common ancestors. Clearly the concept of intelligent design also fits that bill. And intelligent design doesn't necessarily mean God with a big G. Could be aliens. Or devas. Or angels. Or Chuthulu. Or whatever.
The fundamental issue is that evolutionary theory, as stated (and vigorously challenged in various posts by me), seems to merely hold up in two cases that can be experimentally demonstrated, which are: (a) plants, and (b) within a species, that is, breeds. The evidence for species differentiation appears to be inferred. Having a CS background, I know the jokes and understand the dangers that occur when you attempt to prove your theory and end up saying "now, by induction therefore...".
Joke:
The CS prof says: 1 is prime, and 3 is prime, and 5 is prime, and 7 is prime, therefore by induction all odd integers are prime.
(And the physics prof says: 1 is prime, and 3 is prime, and 5 is prime, and 7 is prime, and 9 is, uh, experimental error, and 11 is prime, and 13 is prime -- therefore all odd integers are prime within the bounds of experimental error.)
So whenever I see the bio types in their experiments say: well, it would take too many generations, and too long, and too much money to actually prove this, so therefore we infer that species differentiation would eventually result, therefore evolutionary theory has been proved, QED...I am not willing to accept their inference as evidence.
But the dna mutations can be arranged into a tree structure. And when you do so, it's the same tree that was earlier found by biologists.
Clearly the concept of intelligent design also fits that bill
What is not compatible with intelligent design (but is compatible with stupid design) is the existence of shared errors in the dna of related species.
There's no reason to postulate a designer that mimics natural processes.
The evidence for species differentiation appears to be inferred
Inferred from evidence. Like I've argued on other (?) crevo threads, the presence of shared defects in dna can be explained in several ways: it was designed that way, the mutations occured independently in different lineages, or the mutation ocured once and has been inherited in the different lines.
It might (or might not) make sense for a designer to make use of common parts - it doesn't make much sense to me that both chimps and apes (to use my favorite example) should have been 'designed' to be susceptable to scurvy, by using the exact same scurvy mutation.
The notion that the same mutation occured independently is very unlikely, assuming that mutations are more-or-less random. So far, that's what the evidence shows.
So we're left with inheritence. No hypothetical designer, no special mutations. Just plain old heredity. Seems like the most likely inference to me (and almost all biologists and biochemists). Not to mention the fact that it matches an inference made by other, independent, observations. When distinct lines of inquiry lead to the same conclusion, most people consider this evidence that the conclusion is valid.
Well the way I see it the two major possibilities are:
1. Common descent from a single ancestor, or
2. The intelligent designer went to quite a bit of trouble to make it look like it.
The relatedness between species extends to arbitrary codon usage for specific amino acids (Is there something special about 'UGG' that is should encode for tryptophan in every organism?), shared errors and other oddities.