The Developmental Hourglass Model

An Arabidopsis thaliana flowerWe’ve seen plenty of occasions where the science of embryology has been dragged into the creationism-evolution fight, usually relating to Haeckel’s infamous drawings. This topic of debate has tended to stay within the animal kingdom, but a recent paper in Nature gives an opportunity for Jeffrey Tomkins to expand it’s scope into the realm of botany. He writes: Plant Embryo Development Supports Creation. That seems to be a bit of a stretch.

Embryology confuses me, I must admit, but from what I can tell the point of the paper is to report that plants follow a “developmental hourglass” that has previously been observed in animals. They explain:

Animal and plant development starts with a constituting phase called embryogenesis, which evolved independently in both lineages. Comparative anatomy of vertebrate development—based on the Meckel-Serrès law and von Baer’s laws of embryology from the early nineteenth centuryshows that embryos from various taxa appear different in early stages, converge to a similar form during mid-embryogenesis, and again diverge in later stages. This morphogenetic series is known as the embryonic ‘hourglass’, and its bottleneck of high conservation in mid-embryogenesis is referred to as the phylotypic stage.

This is a little different to the straw man that Tomkins portrays when discussing the evolutionary take on the results. But we’re getting ahead of ourselves. Tomkins opens with the following:

A recent paper that was published in the journal Nature uniquely illustrates the Creator’s hand in plant development. This research clearly shows how suites of protein-coding genes are turned on and off during embryogenesis—the process of generating a plant embryo or seed. The genes are unique to that specific kind of organism and follow an expertly designed progression of gene expression that roundly refutes evolutionary presuppositions.

While this intro would suggest that he is merely making a complexity = design argument, I’ve already established for you that he isn’t. Before we get to it, however, he lays out his own definitions of some terms:

In the mind of an evolutionist, genes with similar DNA sequences across diverse types of organisms are called “highly conserved” and are thought to be ancient (derived from distant ancestors). In light of intelligent design principles, similar genes across diverse organisms serve as basic engineered units working in common core biochemical functions.

Further, evolutionists refer to genes that are very different between organisms as more “highly evolved” or “recently derived.” In a creation-based model, these genes are likely to represent the genetic uniqueness that God chose to characterize each created kind.

All you really need to know is that some genes are older than others, and that a) these genes are also the ones that appear in more organisms and b) creationists vehemently disagree about the ‘older’ part.

For this study, geneticists experimented on a small mustard-like plant that has been widely used in research. They examined two classes of protein-coding genes—”ancient” and “recent” (otherwise known as “core” and “unique”)—and tracked their levels of expression across the different stages of plant embryo development.

In a traditional Darwinian scenario, one would expect the “ancient genes” to predominate early in development and then generally faze to more evolutionarily advanced “young” genes. However, in this study, the “ancient genes” exhibited a fairly constant expression across the stages of development.

Here’s the straw man: Tomkins’ “traditional Darwinian scenario” seems to be his own, possibly Haeckel-inspired invention. The authors of the paper certainly didn’t think that, and he simply asserts it and expects us to agree.

In contrast, the “young genes” showed a burst of expression at the beginning of embryogenesis, right when the embryos should have reflected their most ancient evolutionary beginnings. They then slowed down towards the middle and dramatically increased again towards the end. The data indicated that the “young” (unique) genes, in particular, precisely specified each developmental stage in strong support of the creation model.

Now, how does that “support the creation model”? The “it’s complicated” argument seems to be back again, but I think his real point is to argue that God effectively starts with a template of base genes, which are then made to create diverse organisms by addition of other genes. That still doesn’t explain the observed hourglass however. The beginning and end are the places where it is easiest to incrementally modify the development process. God doesn’t have to worry about difficulty, however.

Skipping to the conclusion:

These unique discoveries refute evolutionary origins and strongly support creation. Plants and animals deploy just the right genes in just the right amounts and at just the right times, as though they were created after their kinds to develop according to their unique genetic blueprints.

That’s a pretty textbook creationist misinterpretation of a study there. I’ll leave the specific problems with this paragraph as an exercise to the reader.

3 thoughts on “The Developmental Hourglass Model

  1. Aha — it’s the old:

    1.Here’s how I imagine that evolution should act/

    2. Here’s a single example where my vague speculations don’t hold up.

    3. Ergo, evolution is disproved.

    Try getting that past scientific peer review

    • It can be worthwhile to put a response of your own to such things, as the creationists often reveal ways that the general public can misinterpret your research. But I’m glad you liked what I wrote.

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