Yuck. Stephen Meyer addressed me on Twitter — that site really has become a cesspool. Anyway, he claimed I hide my evilutionist views behind complexity, so I had to address that. Because it was so stupid.

Also, I’m really annoyed when they drag out deceased scientists who despised them and prop them up as arguments against evolution.

Hey friends!

Stephen Meyer has called me out on Twitter! Well not really Stephen Meyer — by his “staff”. I’ve always found it weird when someone has a “staff” that posts on Twitter under their name, but OK, you be you Mr Meyer. Also it’s not really about Meyer, since he’s just promoting an article by a guy named David Swift who is criticizing me. But sure, Stephen Meyer is poking me at about the third remove, so I’ll bite. He quotes this David Swift fellow saying

@pzmyers “simply uses “complexity” as a smoke screen to avoid facing up to the possible falsification of evolution.”

That’s a strange and ironic comment coming from the Intelligent Design camp, since complexity is their one argument. It comes from the Swift article, where I’m accused of contradicting myself and speaking out of both sides of my mouth, trying to claim evolution is both simple and complicated. Swift says

Can there be a better example of trying to argue that whatever the evidence, evolution is the answer? Where the evidence is consistent with common descent, then of course that is the explanation — it’s simple. And where the evidence is not consistent, common descent is still the explanation — but it’s complicated! Myers simply uses “complexity” as a smoke screen to avoid facing up to the possible falsification of evolution.

Caught me. Although I do have to mention that the evidence observed so far IS consistent with common descent — he’ll have to show where it isn’t. He doesn’t. He also hasn’t come up with a possible falsification of evolution.

In my defense, though, I will point out that biology is both simple and complicated. This has been an issue in natural history for centuries, at least. On the one hand, we observe all these similarities between organisms that link them. Tetrapods all have similar limb structures, homologous bones making up upper limb and lower limb. But tetrapods also have all these differences, and you’ll never confuse a bat’s forelimb with a whale’s front flipper. A comprehensive theory has to account for both the unity of body plans and the divergence between them, and scientists have worked to resolve that dilemma for a long, long time, and Darwinian evolution does a fine job of it.

To be charitable, the creationists have observed the existence of complexity as well. I don’t bring up complexity as a “smoke screen,” but as a fact, a known property of biology that has to be accounted for in any theory. We can go all the way back to William Paley in 1803, in his book Natural Theology, where he’s documenting all the complexities of, for instance, the human eye. Any biologist would agree, eyes are intricate and delicate and contain a great many indispensable details. The creationists at the Discovery Institute would also agree, life is so complicated that they have a whole category of phenomena that they call “specified complexity.”

Where we differ is in the explanation of the mechanism. Creationists, like William Paley or Stephen Meyer, want to argue that the origin of all that biological complexity lies in a complex creator, an intelligent being who created all the variations in life on earth with willful intent. Scientists, beginning with Charles Darwin, instead proposed that complexity can be generated from simple beginnings by means of relatively simple processes — common descent and heritable variation.

Complexity is the inescapable observation of biological reality. The part we disagree on is whether only complexity can create complexity, or whether simpler phenomena can create increasing complexity. Another thing we disagree on: creationists don’t have any evidence for their creator other than pointing at complexity and asserting that that, in itself is the evidence; evolutionary biologists can instead point at all the evidence from chemistry and biochemistry and molecular biology that our proposed mechanisms are valid, making the creationist assertion factually false.

So don’t claim I’m contradicting myself when I say we have both complexity and simplicity: complexity in outcomes derived from simpler rules compounded by chance and contingency.

Swift has some specific details he wants to address, and unfortunately, his whole argument is contaminated with dishonesty. His claim is that observations of early development in vertebrates contradict old ideas about development, therefore evolution is false. As evidence that biologists got everything wrong, he cites von Baer (who did not accept evolution!) who found that diverse embryos shared morphological similarities in the 1830s, and Haeckel (who was a fervent evolutionist) who proposed the Biogenetic Law in the 1860s, which had already been refuted by von Baer, and which was shortly afterwards discarded by biologists — but not by pop culture, unfortunately — as further evidence accumulated that it was false.

Swift tries to claim that we have ignored the evidence that contradicts our expectations, by lying about our expectations.

Does the early embryonic development of vertebrates support their common ancestry? On one hand, he says that of course the similarities of the vertebrate phylotypic stages are evidence of common ancestry. This used to make sense, because everyone agrees that where organisms have evolved from a common ancestor, we expect their early embryonic development to be similar.

Sneaky. “early development” and the “phylotypic stage” are not synonyms. The similarities at the phylotypic stage are most definitely evidence of a common origin — I’d say in common descent, he’d say in a god — but the variation at earlier stages is interesting and says something about evolutionary change. You don’t get to ignore it! We have all these differences between vertebrates at the gastrula stage, but somehow they all converge on similar forms at the later phylotypic stage. Why? How? What is the force that drives that similarity? Intelligent design creationism has nothing to say about it, nor any methodology to even approach it.

Swift says “everyone agrees that where organisms have evolved from a common ancestor, we expect their early embryonic development to be similar.” This isn’t true. Haeckel was discarded a century or more ago, and we don’t expect recapitulation. We know that every molecule and every stage of development is subject to change, limited by the ability of the change to produce viable organisms. And then he quotes Rudy Raff! Raff acknowledges all of that, but then Swift has to do a little quote mining and removal of context to change the meaning.

One might reason­ably expect mechanisms of early development to be especially resistant to modification because all subsequent development derives from early processes.

Exactly. We expect mechanisms of early development to be “RESISTANT to modification,” not impervious. Raff knew full well about variations that could modify early development. He was an expert in sea urchin development, and one of his classic papers is about two closely related species in which one developed indirectly, through a pluteus larva stage, like most echinoderms, and another that developed directly from a large yolky egg to the spiny adult, completely bypassing the larval feeding stage. He wrote about it in Developmental Biology, and was explicit about how species have acquired “radically altered ontogenies”.

Development in sea urchins typically involves the production of an elaborate feeding larva, the pluteus, within which the juvenile sea urchin grows. However, a significant fraction of sea urchins have completely or partially eliminated the pluteus, and instead undergo direct development from a large egg. Direct development is achieved primarily by heterochrony, that is, by the abbreviation or elimination of larval developmental processes and the acceleration of processes involved in development of adult features. Direct development has evolved independently several times, and in several ways. These radically altered ontogenies offer remarkable opportunities for the study of the mechanisms by which early development undergoes evolutionary modification.

This is a topic on which Raff is a known expert, who has written many papers on variation in early development, yet Swift is trying to marshal him as supporting his claim that “we expect their early embryonic development to be similar.” No, Raff most definitely did not. He actively denied it, as you’d see if you saw the whole quote Swift mangled.

A view of development from an evolutionary perspective is both more confounding and more interesting. Early development is highly evolvable, even among closely related species…embryos of two related species follow different early developmental trajectories, but converge on a similar phylotypic stage. It is important to note that the phylotypic stages of related organisms bear major features in common, but also have evolved significantly.

My general feeling is that creationists, like David Swift and Stephen Meyer, really ought to keep Rudy Raff’s name out of their mouths. I knew Rudy. We met several times at developmental biology meetings. He told me a few things: that he read my blog regularly, and agreed with my perspective on biology, and that he thought creationists were dishonest idiots.

He was right, as they keep on demonstrating.