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The Cambrian Explosion [EvolutionBlog]
After publishing Among the Creationists back in 2011, I started to lose interest in the evolution/creationism issue. I felt like I said what I wanted to say (at least to the handful of people who read the book) and that it was time to move on to other things. Besides, ten years on ID does not seem to have recovered from the big Kitzmiller decision, and lots of people more qualified than I have the creationism beat covered.
Recently, though, I’ve gotten interested again. I’ve slowly been working on my magnum opus about mathematical anti-evolutionism, and I’ve been perusing the most recent ID books to see what they have to say. In particular, I picked up a copy of Stephen Meyer’s book Darwin’s Doubt, from 2013, and plowed through it. Turns out I haven’t been missing out on anything. The book is quite long (over 400 pages!) but says very little.
The book is mostly about The Cambrian Explosion. “Cambrian” refers to the period in Earth’s history from about 541 million years ago to around 485 million years ago, which is to say it is among the most ancient periods from which rocks and fossils have survived to the present. “Explosion” refers to the fact that is from rocks of this period that we first find fossils of animals with features recognizable as belonging to modern phyla. It’s an explosion, you see, because the animals seem to appear fully formed, as it were, and do not appear to be result of a long period of prior evolution.
Creationists love the Cambrian explosion. They’ve been going on about it for years, presenting it as some sort of death blow to evolution. It looks like the animals just appeared out of nowhere! Meyer contributes a lot of spit and polish to the discussion (the young-Earthers must be drooling with envy that their stable does not include anyone who can write as well as Meyer), but little of substance. I’m no expert in paleontology, but I would think that a little common sense is enough to see that there’s nothing here.
Consider first that there are just a handful of places on Earth where rocks of Cambrian age exist. We have just a few fossils from a handful of locations to tell us about what sort of critters were around 500 million years ago. In other words, we know next to nothing about the biodiversity of the time. Our knowledge is even more fragmentary when it comes to Precambrian life. Drawing grand conclusions on so flimsy a base does not seem like a fruitful proposition.
Next, we are speaking of an “explosion” only in the geological sense. There is some debate among paleontologists about how long a period of time we’re talking about, but there’s no question that it is best measured in tens of millions of years. My impression is that the term “Cambrian explosion” has fallen out of favor with paleontologists, precisely because it suggests a much shorter period of time than is really under discussion. Meyer, for his part, insists on ten million years, which is at the very low end of what any paleontologist has suggested. It is crucial for his argument that the explosion be as rapid as possible, but I am happy to accept his figure. Ten million years is an awful lot of time for natural selection to do its thing. Evolution is a slow process, but not that slow.
Meyer writes:
[C]urrent studies in geochronology suggest that only 40-50 million years elapsed between the beginning of the Ediacaran radiation (570-565 million years ago) and the end of the Cambrian explosion (525-520 million years ago). To anyone unfamiliar with the equations of population genetics by which neo-Darwinian evolutionary biologists estimate how much morphological change is likely to occur in a given period of time, 40 to 50 million years may seem like an eternity. But empirically derived estimates of the rate at which mutations accumulate imply that 40 to 50 million years does not constitute anything like enough time to build the necessary anatomical novelties that arise in the Cambrian and Ediacaran periods. I will describe this problem in more detail in Chapter 12 (pp. 87-88).
I think you can include Meyer among the people unfamiliar with the equations of population genetics. Those equations typically have to do with modelling short-term gene flow, and not with drawing grand conclusions about the magnitude of morphological change that can occur in forty to fifty million years. I can’t imagine how Meyer intends to quantify the amount of morphological change that occurred during those fateful millions of years. Nor can I imagine how he is going to work out the values of the Cambrian allele frequencies, selection coefficients, mutation rates, or any of the other variables that tend to show up in the equations of population genetics.
And no, nothing in Chapter 12 does anything to suggest that Meyer knows what he’s talking about.
Then there’s the character of the critters themselves. We’re not talking about Cambrian rabbits, to use a famous example. We’re talking about little wormy things. Lot’s of variations on the “little wormy thing” body plan, but little wormy things nonetheless. Moreover, they are preceded in the fossil record by a handful of Precambrian fossils, which are simpler wormy things still. All of this seems entirely in accord with what evolution would lead you to expect. Then consider that at some point a critter is just too simple for it too fossilize, and it becomes inevitable that you are going to find some jumps in complexity.
So, forgive me, but what exactly is the problem here? Which part of this is supposed to make me think that evolution, which proves its worth in thousands of books and papers each year, and which makes sense of reams of data drawn from every branch of the physical and life sciences, is actually just a lot of nonsense? The little data we have about the Cambrian and Precambrian is entirely consistent with evolutionary expectations, which is probably why the paleontologists who study these fossils don’t seem to think they are seeing any fundamental challenge to evolution. The Cambrian explosion is a problem for scientists only in the sense that there are many possible explanations for it, but too little data for deciding among them.
Meyer goes on for page after page, desperately trying to argue that the Cambrian explosion is too a big problem, the simple and obvious considerations I’ve pointed out here notwithstanding. Experienced readers will notice a lot of standard ID rhetorical tricks in his arguments. Many paleontologists are quoted in ways that make it appear they are totally on board with Meyer’s interpretations, but these quotations are seldom more than a single sentence or even a fragment of a sentence. Why do I suspect that if I track down the articles from which these quotes came I would get a very different impression of what was being claimed?
Heck, the old Stephen Jay Gould quote–the one about the Neo-Darwinian synthesis being effectively dead–shows up twice, neither time in its proper context of course.
Meyer presents some equally dubious arguments about protein evolution, but it’s the same sort of thing. You hardly have to be an expert in molecular biology to be deeply suspicious of his assertions. But we’ll save that for another time.
Several times at this blog I have declared ID to be dead. There is nothing in this book to make me revise that assessment.
Source: http://scienceblogs.com/evolutionblog/2015/06/10/the-cambrian-explosion/
