In the comments on a post made some weeks ago, an exchange has begun between myself and William Gibbons, a creationist, concerning the evidence for evolution. There are several issues there that really can’t be settled for quite some time, but I want to move the main part of the dispute, the evidence for evolution, up here into its own post so it won’t get lost in the shuffle. Examining issues like this and the creationist claims concerning them is important, I think. He asked me to provide the 10 best evidences for evolution and I said let’s just start with one and referred to a statement I had previously made in the comments on that post. That statement is as follows:
If evolution is true, and each of these major animal groups split off from the previous one, then what would we expect? Well, we would expect that since each of these new groups split off from an already existing one, the order of appearance within those groups should be as conspicuous as the order of appearance in general. If the first amphibians split off from fish, then the first amphibians could only be slightly different than fish; if birds evolved from reptiles, then the first birds must have been very similar to reptiles; and so forth. And what does the fossil record show? Precisely that. The first amphibians to appear are the most fish-like, so much so that they retained internal gills and were still primarily aquatic. Over time, amphibians become more and more diversified and less fish-like, with later forms being successively more terrestrial and less aquatic. The first birds to appear are so reptile-like that they would be classified as theropod dinosaurs if not for the feathers. We now have multiple feathered theropod species to bridge the gap, and they all appear very early and share most of their traits with reptiles, not with modern birds. Over time, they diversified and became less reptile-like. The same can be said of the first mammals, which are so identical to the therapsid reptiles that they evolved from that where exactly you draw the line between the two groups is largely academic. And just like the other lineages, they start out with only one or two species that looks just like their presumed ancestor, then over time new branches appear that are successively less like those ancestors and more like modern mammals. This is exactly what evolution would predict. Indeed, if it wasn’t that way, evolution would be falsified. If modern birds appeared all at once in the fossil record, with entirely avian skeletal structure and feathers and fully adapted for powered flight, there would be no way to link them to reptiles, and the same is true of every other major animal group. But they don’t appear that way, and the order in which they do appear is precisely what evolution predicts.
This is called “biostratigraphy”. As you go up the geologic column, from older strata to more recent strata, the types of plants and animals that you find fossilized within them change rather dramatically, but they change in a very specific pattern. In the oldest rocks you find nothing but bacteria and the chemical traces thereof, and that continues for over 2 billion years of the earth’s history. Then you find simple multi-celled organisms in the form of algal stromatolites. Then in the late Precambrian, more complex life forms begin to appear, all marine invertebrates. The pattern continues in this basic order: hemichordates –> chordates –>jawless fishes –> jawed fishes –> amphibians –> reptiles –> birds and mammals. That’s a very rough overview, of course, and there is a lot of detail to be filled in. But the important fact here is that the order of appearance is exactly what one would predict if evolution is true, and within each of those major animal groups we find the same predicted order. Now, from the perspective of a young earth creationist, what is the explanation for this order of appearance? That is the question I posed to Mr. Gibbons. Here is the specific question I asked after posting the above statement about biostratigraphy:
In my response to Patterico above, I discussed biostratigraphy and laid out the order of appearance of the major animal groups. Do you have another reasonable explanation for the biostratigraphic patterns other than evolution? I’d be more than happy to discuss flood geology and “hydrodynamic sorting” and show why it is a complete failure as an explanation.
It is a question he pretty much ignores entirely, instead focusing on whether the fossil record is perfect in a specific evolutionary lineage, the reptile to mammal transition. But that was not my argument. My argument doesn’t deal with a specific lineage, though we can discuss that, it deals with the overall order of apperance of the major animal groups and the order of appearance within those groups as well. This is an argument he does not bother to engage, choosing instead to try and poke holes in one specific evolutionary transitional sequence. Even if he is absolutely correct and there is not enough compelling fossil evidence to show the transition from reptile to mammal (and I would certainly argue that this transition is quite solidly established by the evidence), this would not touch my argument at all. It would not begin to provide a rational explanation for the order of appearance that I detailed. Under Mr. Gibbons’ young earth creationist perspective, which posits that all the major animal groups, indeed nearly all animals and plants (they do typically allow some speciation after the flood these days) were created virtually simultaneously about 6000 thousand years ago and nearly all of whom were killed off in a global flood some 4500 years ago, how does one explain biostratigraphy? Well, since they believe that the vast majority of the sedimentary strata on earth were deposited by that global flood, they can only argue that the flood somehow sorted them that way. But that explanation has a myriad of contradictory assumptions and outright laughers in it. The substance of my argument has been made before, by many critics of creationism and advocates of evolution. Perhaps the best explanation of it was made by Gould in an article entitled Genesis v. Geology:
In “flood geology,” we find our richest source of testable creationist claims. Creationists have been forced into this uncharacteristically vulnerable stance by a troubling fact too well known to be denied: namely, that the geological record of fossils follows a single, invariant order throughout the world. The oldest rocks contain only single-celled creatures; invertebrates dominate later strata, followed by the first fishes, then dinosaurs, and finally large mammals. One might be tempted to take a “liberal,” or allegorical, view of Scripture and identify this sequence with the order of creation in Genesis 1, allowing millions or billions of years for the “days” of Moses. But creationists will admit no such reconciliation. Their fundamentalism is absolute and uncompromising. If Moses said “days,” he meant periods of twenty-four hours, to the second. (Creationist literature is often less charitable to liberal theology than to evolution. As a subject for wrath, nothing matches the enemy within.)
Since God created with such alacrity, all creatures once must have lived simultaneously on the earth. How, then, did their fossil remains get sorted into an invariable order in the earth’s strata? To resolve this particularly knotty dilemma, creationists invoke Noah’s flood: all creatures were churned together in the great flood and their fossilized succession reflects the order of their settling as the waters receded. But what natural processes would produce such a predictable order from a singular chaos? The testable proposals of “flood geology” have been advanced to explain the causes of this sorting.
Whitcomb and Morris offer three suggestions. The first — hydrological — holds that denser and more streamlined objects would have descended more rapidly and should populate the bottom strata (in conventional geology, the oldest strata). The second — ecological — envisions a sorting responsive to environment. Denizens of the ocean bottom were overcome by the flood waters first, and should lie in the lower strata; inhabitants of mountaintops postponed their inevitable demise, and now adorn our upper strata. The third — anatomical or functional — argues that certain animals, by their high intelligence or superior mobility, might have struggled successfully for a time, and ended up at the top.
All three proposals have been proven false. The lower strata abound in delicate, floating creatures, as well as spherical globs. Many oceanic creatures — whales and teleost fishes in particular — appear only in upper strata, well above hordes of terrestrial forms. Clumsy sloths (not to mention hundreds of species of marine invertebrates) are restricted to strata lying well above others that serve as exclusive homes for scores of lithe and nimble small dinosaurs and pterosaurs.
The very invariance of the universal fossil sequence is the strongest argument against its production in a single gulp. Could exceptionless order possibly arise from a contemporaneous mixture by such dubious processes of sorting? Surely, somewhere, at least one courageous trilobite would have paddled on valiantly (as its colleagues succumbed) and won a place in the upper strata. Surely, on some primordial beach, a man would have suffered a heart attack and been washed into the lower strata before intelligence had a chance to plot temporary escape. But if the strata represent vast stretches of sequential time, then invariant order is an expectation, not a problem. No trilobite lies in the upper strata because they all perished 225 million years ago. No man keeps lithified company with a dinosaur, because we were still 60 million years in the future when the last dinosaur perished.
I hope Mr. Gibbons will return and engage my argument directly.