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The Deeper Issues of the Worm Video Debate: P.Z. Myers's Misdirection

Recently, both Jerry Coyne and P.Z. Myers posted criticisms of the new video from Discovery Institute, "How to Build a Worm." Quelle surprise, they didn't like it -- but the genuine surprise was the contribution of distinguished evolutionary biologist Ursula Goodenough of Washington University. Goodenough also commented on the video, and tried to solve the problem it raised. Her solution fails, but its failure is instructive, because it reinforces the main point of the video: whatever brought the process of animal development into existence must have been a cause with foresight.

We'll look at Goodenough's proposal another day. First, let's move the rubbish to the curb.

1. Clearing Away Errors and Irrelevancies

We can ignore Jerry Coyne's post, because he only fussed about the video for a handful of paragraphs, saying nothing of substance. For his part, P.Z. Myers wrote at length, but most of it was either wrong or irrelevant.

  • Myers needs to read the sources he cites.

Myers accused me of not knowing the history of cell-lineage research, and cited the classic work of E.G. Conklin on ascidian embryos as evidence. In the video, I said this:

For the first time in the history of biology, we were able to see and track the development of an animal from one cell to the adult. ... to have that in the detail, right down to the level of individual cells, that's incredible.

"Nope," writes Myers, "People have been tracking cell lineages in embryos for over a hundred years," and concludes that my understanding of the topic is "sloppy and shallow."

He needs to watch the worm video again, and actually read Conklin's 1905 monograph. I said -- note the emphasis -- "from one cell to the adult...right down to the level of individual cells." Conklin didn't do that, namely, trace the lineages in ascidians from the fertilized egg to the adult, cell by cell. No one did, in any animal group, until Sulston's groundbreaking thoroughness with C. elegans in the 1970s.

Conklin himself explains that he stopped tracking lineages at the 218-cell stage in ascidians:

Beyond this point I have not attempted to follow the lineage of each and every cell; this could be done successfully only by a most exacting study of serial sections in connection with whole preparations. With sufficient labor and material I believe that the lineage of every cell could be traced through to the tadpole stage, but I have lacked both the time and the material for such a study. (1905, p. 67)

The tadpole stages of ascidians such as Ciona or Halocynthia exhibit well over 2,500 cells, ten-fold in number past the point where Conklin quit. Reproductively capable adult ascidians, of course, possess many more cells than that.

Thus, Conklin's work, while beautiful, doesn't contradict what I said in the video. My reading of the historical significance of the C. elegans research breakthrough, by the way, isn't controversial in the least: "The introduction of Nomarski DIC optics in the 1960s made it possible for the first time to trace all cells and their divisions in live embryos."

  • The remarkably wide range of developmental architectures within the phylum Nematoda only complicates, but does not solve, the problem of the origin of the specific C. elegans mode.

Myers cites a review paper by Bob Goldstein on the diversity of modes of development within the phylum Nematoda, and says that this diversity shows that "when you look at all of the possibilities, that there are many other alternative ways of achieving similar results, the odds begin to go down and down and down, often reaching the point of absolute certainty."

It looks like Myers didn't read Goldstein's paper either. The inference Myers draws of "absolute certainty" isn't even remotely close to Goldstein's point.

Rather, Goldstein summarizes just how little is known about the evolution of nematode development, observing (for instance) that apparent similarities between C. elegans loss-of-function mutants, and developmental modes in other nematode species, may not be illuminating, "particularly since many of these mutations are lethal in C. elegans" (2001, p. 1523). Basic questions such as the ancestral mode of development within Nematoda -- which must be described if one is going to explain the origin of the specific features of C. elegans development -- cannot be answered, Goldstein says, "with any degree of certainty" (2001, p. 1524). And so on. Nor is the situation any clearer with more recent publications.

In a follow-up post, Myers repeated that the diversity of nematode developmental pathways showed that (in effect) "many roads lead to Rome," giving undirected evolution a high probability of success at producing the specific features of C. elegans development:

A functional end result was selected for, just like in a game of poker, where a winning hand is "selected" -- however it got to that point...there are multiple ways for development to produce a working worm, and I cited a paper that discussed the taxonomic variation present in various nematode species and genera.

But if the differences seen in other nematode groups told us anything about how C. elegans itself evolved, then Myers could tell us where to look in those other groups to find the intermediate stages. Yet he doesn't. Bob Goldstein himself doesn't know -- and he (Goldstein) compiled the data.

Thus the net yield in explanatory insight is nil.

2. The issue isn't the sheer complexity of development; rather, it's the underlying goal-directed logic of the process.

Myers says that I focused on C. elegans because, like ID theorists generally, I'm bewitched by sheer complexity and cannot imagine how it could have evolved via an undirected evolutionary process.

But the poverty of my imagination isn't the issue. If one looks in the biological literature to find the step-by-step evolutionary pathways for the origin of any metazoan (animal) developmental architecture, including those within Nematoda, one will come away empty-handed. Try looking yourself.

Presumably, if detailed accounts were available, Myers or Coyne or Goodenough would have cited them. But -- nothing. Paul Nelson didn't fail to imagine those detailed accounts. Evolutionary biologists themselves failed to do so, which -- if natural selection or other undirected processes are as powerful as claimed -- should strike the reader as exceedingly odd.

Rather, we chose C. elegans for a short video because the system is so well understood as an example of how animal development works -- the nuts and bolts of its functional logic. A much simpler system, however, if one were available, would do as well. So Myers's many paragraphs about my supposed obsession with complexity are entirely beside the point. Complexity is a red herring.

The central problem to be solved, and the only relevant one, is the origin of the end-directed character of animal development, whether complex or simple, via evolutionary processes lacking foresight. Now, while Myers agrees that evolution possesses no foresight, he overlooks the key logical point that natural selection operates only downstream of successful (i.e., functional) novel variations.

Thus, Myers writes:

... the unit of selection is the viable individual capable of reproduction; all selection sees is whether this organism manages to replicate itself. There is selection against individuals that fail to produce testes or a gut, and of course there can be selection for individuals who can produce elaborations of their form that enhance the reliability of replication.

True -- but if "the viable individual capable of reproduction" is a developing animal like C. elegans, the embryo must first evolve, and somehow cross the time and space represented by cell division and differentiation, when it cannot yet reproduce itself. Given that reproduction is a necessary condition of natural selection, however, selection is powerless to act until reproductive capability comes online. Randomly arising mutations must therefore construct novel developmental pathways "on their own" -- with crash-and-burn of the whole system as the most likely result.

Ursula Goodenough's proposal to solve the problem shows this unmistakably, as we'll see in a follow-up post.

References:

Conklin, E.G. 1905. The Organization and Cell-Lineage of the Ascidian Egg. Journal of the Academy of Natural Sciences of Philadelphia, 2nd Series, Volume XIII.

Goldstein, Bob. 2001. On the evolution of early development in the Nematoda. Phil. Trans. R. Soc. Lond. B (2001) 356, 1521-1531.