Evolution Icon Evolution
Intelligent Design Icon Intelligent Design

A Critic Asks: Doesn’t Our C. elegans Video Commit the Post Hoc Ergo Propter Hoc Fallacy?

archer nelson.jpg

A few points relevant to the new release, “How to Build a Worm,” from Discovery Institute:

1. Does the video about C. elegans employ illicit “backwards” reasoning?

“How wise of the Creator,” a lady is said to have remarked to a philosopher in an apocryphal exchange, “to have designed all the major rivers of Europe to run through its main cities.” “And our noses were perfectly placed,” a friend of hers added, “to support our spectacles.”

Struck speechless by this double-barreled blast of blissful illogic, the philosopher could only manage a wan smile and shake his head.

A YouTube commenter, Vimal Ramachandran, argues that the video we just posted suffers from the same post hoc ergo propter hoc (“after this, therefore because of this”) fallacy. This merits a response. He wrote:

This is nonsense. Paul Nelson, you’re making the mistake of looking at the end result — a worm with muscle, nerves, germ cells, and intestine — and concluding that this was the only possible outcome. Therefore, everything should have been programmed upfront to produce this particular creature with this particular characteristic. You then liken this to human architects who plan ahead to work towards a pre-decided end result.

But this is wrong and you won’t understand evolution unless you free yourself from such teleological thinking. We know of even simpler animals that don’t have such well-differentiated tissues or developmental patterns — sponges, cnidarians, ctenophores, placozoans, all of which are evolutionarily even more ancient than C. elegans.

Thus, we can see that animals don’t have to have nerves and muscles to survive, they started out as mere colonies of daughter cells, gradually acquiring specializations through evolutionary time. Different mutations produced different animal lineages which went different ways. One lineage led to the ancestor of C. elegans and its cousins including us. Random chance events and adaptation can explain this because the way C. elegans ended up was just one among countless possible outcomes, out of which only one outcome stuck. This outcome stayed on because it was good enough to produce a creature that can survive enough to reproduce in its given environment.

Likewise, another outcome stayed on for placozoans and yet another outcome stuck for sponges. It is wrong to look at the end result and see teleology. Rather, you must appreciate the role of how chance and contingency can produce diverse patterns from a simple beginning. I’m worried about young students who will be misled by such wrong propaganda.

To which I can only add: of course.

Of course animals don’t need to have the anatomical features or the developmental pathways of C. elegans. Sponges don’t, nor do placozoans, nor do cnidarians, or ctenophores — and so on.

But that’s not the problem. C. elegans does need its specific features. And that IS the problem to be solved.

Let’s assume that all animal species, including C. elegans, share a common ancestor, which is what evolutionary theory claims. This geometry entails — necessarily requires — a sequence of intermediate forms leading to C. elegans from its unicellular eukaryotic ancestors. Now, whatever those intermediates happened to be, the lineage they constitute must arrive at C. elegans, with all of its developmental details and features, somehow. The target for explanation is thus provided by nature herself.

Saying this doesn’t invoke teleology or post hoc reasoning in the least. Rather it’s a straightforward deduction from the existence of C. elegans, given the theory of common descent. If C. elegans indeed evolved by an undirected historical process, the lineage leading to the species through space and time, from other different species, must have existed. And the target of interest, namely, C. elegans itself, is here today and requires explaining, whether we assume teleology or not.

So what evolutionary lineage constructed C. elegans?

2. Focusing on what’s relevant

Suppose your doorbell rings, and you open the front door to find me standing there. You live on the 37th floor of an apartment building, at the end of a long brick hallway with no other doors or windows. The building has one elevator reaching the 37th floor, a single stairwell, one public entrance with a security desk staffed at all hours, and is located in Manhattan.

These facts constrain the possible explanations that we can reasonably consider about how I came to be standing at your front door. To say, “But Paul could have gone to hundreds of other apartments in that building, or to another building altogether, or to Boston, or London,” is true, but strictly irrelevant. Those possibilities concern other outcomes — but not the explanatory target of interest. If we wish to explain why I am standing in your hallway, that’s the universe of relevant information. Likewise, if we wish to explain the origin of C. elegans, focusing on unrelated species only defers the task, or misdirects our attention to irrelevancies.

Vimal Ramachandran writes:

…animals don’t have to have nerves and muscles to survive, they started out as mere colonies of daughter cells, gradually acquiring specializations through evolutionary time. Different mutations produced different animal lineages which went different ways. One lineage led to the ancestor of C. elegans and its cousins including us.

Okay, let’s go with this hypothesis. Here are some questions that must be answered:

  • What colonial (or other) species were the ancestors of C. elegans?

  • How did cells in those species gradually acquire the specializations seen in C. elegans?

  • What mutations in those species produced the anatomical features or developmental pathways of C. elegans?

Nobody knows, including Vimal Ramachandran — which is why his explanation is so hopelessly vague and hand waving. Once one begins actually to grapple with the precise details of C. elegans development, for instance, “gradually acquiring specializations” immediately turns into a just-so story of zero value.

3. This problem won’t go away, and calling it teleology won’t make it go away

The point of the videos is to highlight what needs to be explained when we come to a well-understood system such as C. elegans. In particular, the origin of the developmental stages between fertilized egg and reproductively capable adult are hard (or impossible) to explain via natural selection. This problem was the topic of my poster at the 2014 annual meeting of the Society for Developmental Biology.

Vimal Ramachandran’s objections would be weightier if they had any genuine substance. I’ll stick with the evidence.