Whenever I spot some old thread suddenly getting a surge of new comments, I can guess what has happened: a creationist or two has come to visit. That’s happening right now on this very short article that mentions the peppered moths; we’re up above 200 comments now, and it seems to have very little to do with moths anymore. Instead, we’ve got a creationist complaining about the absence of transitional species and the Cambrian ‘explosion’, with a little quote-mining of Richard Dawkins. You commenters are taking care of him ably, but there are just a few things I want to mention, and a few questions I want to ask of the creationists.
First, the quote mine. This creationist plucks out a quote from Dawkins that Dawkins himself has already addressed:
I once introduced a chapter on the so-called Cambrian Explosion with the words: “It is as though the fossils were planted there without any evolutionary history.” Again, this was a rhetorical overture, intended to whet the reader’s appetite for the explanation. Inevitably, my remark was gleefully quoted out of context. Creationists adore “gaps” in the fossil record.
There are a great many mysteries in our histories. For instance, my aunt’s genealogical research revealed that I have a great-great-great grandmother named Zerusha, with no further information on who she was. I do not interpret this to mean that she was conjured out of thin air or deposited on this planet by visiting aliens or that she stepped out of the forehead of a god; I think it’s highly likely that she, like my other relatives, was a human being with her own ordinary but interesting biography, which has merely been lost to me. Missing data doesn’t imply miraculous origins, whether it is my recent human ancestors or the many-times great grandparents of trilobites, over half a billion years ago.
I would ask creationists two questions about this. Why do you even bother to take quotes out of context from people like Dawkins or Darwin or Gould or Gee or Patterson? You know they aren’t expressing doubt about the theory of evolution. These are authorities who are well aware of the wide range of evidence available and have firmly ensconced themselves on the side of evolution, and so we all know immediately that you’re up to something dodgy when you try to pretend Dawkins is on your side with a fragment of a quote. You don’t catch us trying to recast D. James Kennedy as a firm believer in the science of evolution, after all, so it’s more than a little weird when you try to weave the illusion that Darwin was a defender of creationist thought.
And then I’ve always wondered why you think a transition that is incompletely understood is evidence against evolution. It’s not, you know; it’s not as if we’ve been saying for years that the beautiful transitional fossils leading up to the first trilobite are the sole evidence around for evolution. We’ve got people saying we don’t have a good picture of the pre-Cambrian origin of arthropods, but we do have good evidence for organisms like cetaceans or humans, and we’ve got all these lovely molecular connections between various lineages, so trilobites are an interesting problem. Do you have this odd idea that the only good explanations are complete ones that pin down every possibility and answer all questions? Because your own bible or the musings of your favorite IDist don’t even come close to accomplishing that, you know.
And then we get these astonishing declarations: “The fossils embedded in the Cambrian strata are quite inconsistent with what we would expect from Darwinian evolution.” I have heard that phrase quite often; usually it quickly emerges that our intrepid inquisitor doesn’t know anything about the distribution of fossils in and before the Cambrian, and has some weirdly distorted view of what evolutionary theory would predict. In this case, our creationist doesn’t seem to know what lagerstätten are, hasn’t read any of the paleontological literature, and in fact is operating entirely on the fumes from creationist bloviations on the subject.
Here’s a recommendation. If you want to talk about the evolution of trilobites, you don’t have to read a technical review like Valentine’s On the Origin of Phyla(amzn/b&n/abe/pwll) (it’s very good, but it isn’t light reading; I have a short discussion of a relevant part of the story online, though). You should, however, know something about the subject, and third-hand distortions filtered through your local minister or Ken Ham or the Discovery Institute don’t count. I recommend Trilobite: Eyewitness to Evolution(amzn/b&n/abe/pwll) by Richard Fortey as a good introduction — it’s readable and entertaining.
(NOTE: do not read it with a plan to quote-mine Richard Fortey. He’s far more familiar with the physical evidence than you are, and he’s strongly pro-evolution. Coming back from that book having ignored all of the substantive content and arriving at the conclusion that Fortey has a few phrases that can be used to shore up your claim that trilobites were created by magic or alien technology 520 million years ago means you really are an idiot, because Fortey definitely does not provide any support for that thesis.)
Here, for instance, is a simpler, cleaner version of a similar diagram you can find in Valentine. We don’t know specifically what the direct predecessors of the trilobite lineage were, but it’s not as if everything went poof at one instant at the beginning of the period, 545 million years ago.
Hints and fragments and little traces bridge the Precambrian-Cambrian transition. Think about what a trilobite is: a small (mostly) armored arthropod. Think about what its predecessors would have been: small or smaller partially armored arthropods. Think about what their predecessors would have been: small or smaller unarmored bilaterians, soft wormlike burrowers. Now look at that diagram, and what do you see? A period of soft-bodied creatures that fossilized poorly and only under remarkable circumstances, followed by the appearance of burrows and other trace fossils and odd fragments of partial cuticular armor (the ‘shelly fauna’), and then, later, fossils of animals like the trilobites that have complete armored exoskeletons that fossilize relatively easily. And all of this is over a period of millions of years.
If you ask me, what evolution predicts we should see in the evolution of trilobites and what the fossil record actually shows us are in pretty good concordance, even if we are missing big chunks of the story. The mystery of the Cambrian isn’t how an individual lineage emerged, but why so many different animal lineages evolved in parallel towards larger size in the same relatively narrow window of time — we’re looking for mechanisms of coordination of evolution of different phyla.
Now here are some more puzzlers for the creationists. When rational, sensible people, geologists and paleontologists (and many of whom are actually Christians and believers of various sorts), look at the evidence, we see that the history of the earth was old and complex, rich with successions of very different flora and fauna, and with the hallmarks of transitions — that is, the beasts of the field didn’t just appear in an instant, but over long periods of time, and with apparent ancestral forms in deeper periods of time. They came to these conclusions in the 19th century, before Charles Darwin proposed mechanisms that would drive change in biological lineages. This is an important but apparently very subtle distinction: even Michael Behe gets it, while most creationists don’t. Evolutionary change and the revealed pattern of history is inarguable and distinct from whatever mechanism is proposed for it. So why do you argue against a specific Darwinian mechanism by arguing from ignorance against the facts of geology and paleontology? It doesn’t make sense.
Let me make this concrete with a simple analogy. My family and I have slowly worked our way across the country from the 1980s, when we lived in Oregon, to now, when we live in Minnesota. We have a few photo albums that show our younger selves in a series of places, from Oregon to Utah to Pennsylvania to Minnesota, but we don’t actually have gas receipts or video tapes of our drives between those places, when we’d pack our belongings into a truck and make the actual moves.
Now imagine that we face a group of anti-transportationists — they don’t believe we did that. Sure, they believe in micro-transportation, like short commutes from home to work and back again, but macro-transportation where whole households can move thousands of miles must be impossible. When I show them my family album, they’ve got two responses. One, my pictures are faked, we couldn’t possibly have come from Oregon, ever, and those are different people with no relationship to us — people arise suddenly in one place and never go anywhere else. The other response is that sure, that might be a photo of me and the wife on a beach in Oregon, but trucks were impossible in the 1980s — we were actually lofted to Minnesota in a flying saucer piloted by Jesus. Each response on its own could be addressed in some detail, except that these nay-sayers use both, unaware that they’re mutually contradictory.
If I dig up additional documentation, school records and tax forms that show I actually lived in Utah, for instance, they might briefly concede the point, only to shift gears and claim that the Oregon-Utah transition could not have been handled by these mythical “trucks”, and we get the cargo-carrying UFO story. If I point to existing trucks and calculate rates of movement and fuel use, they say that maybe in theory such a thing is possible, but I still can’t show a mile-by-mile log of every step of our journey, and look, that photo on the Oregon beach shows a more slender, youthful fellow — that’s not the Myers they know. It’s the creationist two-step. They juggle two inconsistent rebuttals, never quite getting to the point where they look at both and notice that they mutually annihilate each other.
And of course the final irony of the debate is that they pretend to know more about that personal history than the people who spent 20 years working through it, in detail.