Because -- as you well know -- most of the creationists on these threads reject the notion of common descent. So why the red herring?
Now how about this? This chemical analysis of DNA structures also showed something else. The spread of the Alu DNA repeats was written into the chemistry of human chromosomes. The process was not random, Dugaiczyk said, and it was not subject to an environmental "natural selection," separating winners and losers as theorized by Darwin.
Well, since you asked... It's sloppy thinking, and I don't see how the researcher could possibly claim to have determined such a thing.
Doctor Stochastic seems to have access to the original paper (I don't have a PNAS subscription, and don't consider it worth a $10 purchase just to look at this one article), perhaps he could describe what, if anything, the researchers actually did to support Dugaiczyk's assertions.
Let's take that paragraph a line at a time:
The spread of the Alu DNA repeats was written into the chemistry of human chromosomes.
Vague, to say the least. Presumably they mean that something in the protohuman DNA resulted in heightened Alu repetition mutations. That "something" would itself most likely be the result of some kind of mutation, which diverged the protohuman cellular environment from the protochimp cellular environment. Good enough, but then he gets weird in the next sentence:
The process was not random, Dugaiczyk said,
Which "process", exactly? The original change which resulted in heightened Alu production? The Alu production itself? The mutations resulting from the recombinations of the new Alu repeats? No matter which process(es) he meant, it's highly unlikely that he could have actually established that the process was "not random".
Or maybe he's just speaking poorly, and he means that once the cellular environment was altered (presumably randomly) in order to favor heightened Alu production, the outcome (i.e., increased Alu repeats) was a deterministic result of that modified environment, and was not itself due to additional random Alu introductions. If so, then his statement would be accurate, but hardly significant enough to mention as if it was some sort of discovery worth making a fuss about. It rates high on the "yeah, so?" meter.
and it was not subject to an environmental "natural selection," separating winners and losers as theorized by Darwin.
I hope this is just the science reporter presuming too much, instead of any assertion from Dugaiczyk himself, because Dugaiczyk should know better.
There are two opposing possibilities:
1. The result of the Alu repetitions were "silent" -- that is, although present in the human DNA, they make no difference whatsoever. In this case, it would be accurate to say that they were "not subject to natural selection" (in fact, it would be pretty much true by definition), but this would also be a trivial result. It would mean that the Alu repeats were *not* involved in whatever DNA differences made us human.
2. The result of the Alu repetitions were *not* "silent" -- that is, they made some contribution to whatever DNA differences make us human. In that case, they *would* actually be subject to natural selection, just like any other phenotypic difference, and only a fool of a scientist would try to claim that he had been able to show that they wouldn't be.
So something's very wonky with the paragraph. I'm going to point the finger at the science reporter unless the paper itself is actually foolish enough to make such claims, which I highly doubt.
This should also serve as yet anothe reminder to Michael_Michaelangelo as to why it's important to actually read the primary sources, and not go flying off half cocked as the result of a "pop science" blurb about it. If I recall correctly, this isn't the first time I've reminded him of that.
It doesn't look as if they demonstrated any mechanism at all; in their conclusion, the point out that they haven't done so. They have demonstrated a different mutation rate for the AluYb28 elements between humans and chimps. The authors claim that this increased rate is not explained by selection, however they do not give any model for selection to say why. (I think this is rather incomplete on their part.) The authors also seem to use "random" to mean "uniform" which is a bit of a concept conflation. Later they point out that even knowing the structure around the AluYb8 patterns, one cannot predict where the next transposition will occur; I don't see how this is different from "random."