Today's organisms are phylogenetically descended from others which were vastly simpler than they are, so much simpler, in fact, that it's inconceivable how any kind of description of the later, complex organisms could have existed in the earlier one. John Von Neumann
There are numerous grades of creationist arguments, from those that willfully ignore the convergent evidence from multiple branches of science, to those that make every effort to conform to available evidence without dispensing of that added element, the cosmic designer. The notion of "frontloading" falls into the latter. The idea seems to be that:
*Evolution did indeed proceed from a primordial common ancestor.
*Further tinkering may not have been necessary, but the potential for all sorts of otherwise impossible complexity was built into the DNA from the very beginning. Over geological time, organisms unfold into more complex, higher forms. Evolution, in other words, was directed from the very beginning.
Typically, a frontloader gets excited if/when some journal reports on a gene that serves no immediately obvious function in a creature that resides in a low position on the evolutionary tree, but is important for higher organisms. An example would be precursors for nerve tissue found in some sponges. Unlike the folks who do the research and write the articles, these frontloaders are quick to speculate that the gene in question was somehow embedded for future generations and is worthless for the sponge.
Despite the attempts to move the ID goalposts right out of the stadium, there are big problems with frontloading:
1) Exactly how many genes needed to be loaded into the primordial organism to encompass all of life's diversity over the last 4 billion years? Presumably, any genes that IDers typically label "irreducibly complex" (e.g. those for the blood clotting cascade) must be included here.
Michael Behe takes a particularly, uh, nuanced view on the subject. Some of his remarks seem to suggest he's not averse to a frontloading scenario. And he claims to endorse "common descent". On the other hand, he also argues that the majority of the 10,000 or so protein/protein interactions in a typical mammalian cell exhibit irreducible complexity. That's just one species! For a Behe-frontloading scenario to work, tens of thousands of different protein coding sequences would have to be packed into the primordial organism.
2) How were these useless genes preserved over 3 billion years or more? Useless genes, of course, have a habit of getting excised from the genome, so we should see evidence of some sort of mutation-checking system that is so powerful that a wide variety of genes can be passed through trillions of generations without so much as a single base pair substitution. We don't see that, and it's not for lack of trying...biochemists would love to get their hands on enzymes that copy with such fantastic fidelity. It's funny to see the same folks who have offered up so much blather on the topic of "genetic entropy" reverse course and speculate that certain useless genes have been passed through lineages unscathed for eons.
Then again, there seems to be another breed of frontloader who argues that none of these ancient genes were actually useless. They simply served functions other than what we see today. That's great...it's the same argument that biochemists have offered the IDiots to dispute "irreducible complexity" for the last 20 years (e.g. on its own, the spring mechanism of a mouse trap won't catch mice, but it will serve nicely as a tie clip).
3) Where are all these buried genes now?
I can see some "outs" for the above questions. As for the buried genes, IDers can wiggle out of that dilemma by fantasizing that we've reached the evolutionary juncture where all such genes have been jettisoned and are thus, conveniently, not available for study. With the advent of humanity, you might say, all biological innovation pooped out. Awfully sci-fi.
It's possible to imagine some sort of DNA or RNA software package that compresses a huge diversity of genetic outcomes into relatively few base pairs. I'd call this program "evolution", but the frontloaders must also explain how their pet examples of "irreducible complexity" get compressed and maintained in the primordial .zip file. If you respect the authority of Von Neumann, that's one hell of a hurdle.
Should I try to make that bacterium sweat, or grunt with effort?