A creationist writes in espousing the Argument from Incredulity

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I’m no ID supporter, but when I read replies like this to tough challenges (like complex symbiotic relationships) that exist, my response is that this feels like a “Response from Incredulity”… I know that is not an actual thing, but why would this response, which lacks specific data to support it, be any more viable than the initial challenge, which is admittedly an argument from incredulity?

In the case of the wasp, all that is required is that different larvae have different propensities to eat the organs of the spider. How could this happen? Well, presumably the different organs of a spider can be perceived differently by the larval wasp, either by their location or, more plausibly, by the fact that they “taste” different. If different wasps prefer different “tastes” (or internal locations), and some of that variation is based on variation in genes, then the problem is solved. That’s because those wasps with a taste for the vital organs, or for indiscriminate eating, will kill their hosts early and stand less of a chance of surviving (edit: DUH…) (if you kill your spider host too early, it decays and will not constitute good, fresh food, so that you may die or be malnourished). On the other hand, those larvae having less of a taste for the vital bits of the spider host, and thus which eat those bits last, will be the ones most likely to survive and leave offspring. Over time, this results in the evolution of a behavior in which all wasps eat the nonessential organs first, only finishing up with the vital ones when they’re about to pupate. Note that there is no conscious “knowing” here: all that’s required is variation in how you eat your host, and you need no cognition for that—only an attraction to eating some organs more than others. And this is not implausible.

Agreed, it is not implausible. But without data to support this claim, it is still as equally implausible as the argument from incredulity. At best, it is certainly no defense against the original question. Granted, one asked “how could this happen” and another answered, “here’s how.” But the response is still a guess without data. Find a gene that switches the “spider organ taste preference” from one organ to another and you have a viable response to the challenge.

@Mercer @Patrick @John_Harshman This seems like opposing views of what makes sense. First for a creationist, and next for a biologist. Am I wrong about this? If so, can you explain how? I’m asking this sincerely, because these are the kinds of questions that creationists and other laypersons have. If the responses are not satisfying, the layperson will feel as though their challenge stands.

The ID argument, in effect, is: “This is implausible; therefore intelligent design is more likely.”

In response, the evolutionist only needs to demonstrate plausibility.

All history is based on sparse evidence, and natural history is not an exception to that. If the only evidence we had was the sparse evidence from natural history, the ID proponents would have a point. But we have strong evidence of ongoing processes of biological change. And the evidence from natural history is consistent with what we see in those processes.


I see, that makes sense.

So then, if one were to have made a different argument, plausibility would not be the threshold, right? What if I were to say this:

Symbiotic relationships such as that of the wasp and spider, wherein the larval wasp engages in eating specific organs of a host spider so as to allow the host to survive–but not to cause it to die prematurely–are described by evolutionary biologists as being plausible. A case can be made for certain larvae possessing a genetic disposition to prefer the organs of the host that are most advantageous to its survival, but is there any evidence to suggest that this organ preference is a malleable trait that changed over time?

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Why does the gene have to be for taste preference w.r.t. spider organs?

We know that there are genes that affect taste preferences, such as the human TAS2R38 gene that causes differing responses to chemicals found in some varieties of Brassica. Given the known existence of that gene, and the known ability for organs to produce diifferent chemicals (e.g. bile and urea produced in livers, but not in brains) any implausibility is reduced from
are there genes that affect taste preferences for spider organs
do insects have similar genes

This is not equally implausible.

Brussel sprout preference in humans is a malleable trait that can change over time. Organ preference in wasp larvae could be too.


I don’t know, but this is how the original article described the process as being plausible.

This is a very good example. I think that this kind of explanation adds value that can be comprehended by the layperson, who would be prone to putting forth this kind of challenge. That said, having data that could explain this specific plausible scenario and using it as an example would be much more effective.

These kinds of questions are significant obstacles for laypeople like me. The more effective the response is in providing a plausible pathway, the better.

I think so. I think you mistake an argument for plausibility, as in the wasp, for an argument from incredulity, as in creationism. The argument for plausibility presents a possible pathway to explain the existence of some feature. The argument from incredulity says that there is no plausible pathway, therefore God did it. They seem polar opposites to me. The argument from incredulity is much weaker, perhaps self-contradictory: we don’t know how this happened, therefore we know how it happened.


Thanks John, that makes good sense. There are so many incredible examples of symbiosis in nature. I’m wondering if there’s an “icon” (pun intended) for symbiosis that can be presented as an example. A case could be made that the plausible pathway is simply implausible, absent data that supports such an explanation.

I don’t believe that’s true. These cases rest on the general observation that there is genetic variation in just about every trait we see, so it’s not a great leap to infer that there should be genetic variation in, for example, larval feeding behavior. I don’t immediately think of an icon of symbiosis, but what may be relevant here is the general trend for diseases to become less quickly fatal over time.

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As a suggestion from the gallery, this would be the kind of data/information that would really help those who have substantial questions like this one. Plausibility is rather subjective, as we know.

Indeed. We are all guilty of hypocrisy at some point or at some level, but it does get a little deep in these types of creationist screeds. What the creationist is asking us to accept is that a supernatural deity created these species, fully formed, and expects us to accept this explanation with no evidence to support it. Therefore, it is a bit rich when creationists demand evidence for a very specific natural pathway when they don’t require any evidence for the explanation they already accept. This is where an argument from incredulity morphs into an argument lacking credibility.

Plausibility arguments are very specifically responses to the argument from incredulity. If there’s a plausible pathway, the argument from incredulity is defeated.

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I respect what you are saying here, but I think that you are missing my point, entirely. The point is that symbiosis presents a legitimate challenge in the eyes of every layperson. I’m not trying to measure the validity of one response vs. the other. I’m merely saying this:

  1. Suggesting an explanation for the wasp / spider sympbiosis as Jerry Coyne does in the article linked above is no more satisfying to the layperson than the creationist objection is to the evolutionary biologist.
  2. If scientists can identify one example that is backed by data that can serve as an “icon for symbiosis”, the explanation will carry more weight.

No one is demanding anything. Having an example that is backed by evidence would absolutely bring the conversation to an end. If an example doesn’t exist, so be it. If it does, it would go a long way toward ending this type of objection.

In the vast majority of cases, I think it is only viewed as a challenge in the eyes of people who already reject evolution. It doesn’t take much time to figure out why symbiosis would be selected for.

That’s doubtful. Look at all the transitional fossils that have been found. We still hear creationists claiming that they refuse to accept evolution because there are no transitional fossils. When the objections aren’t based on logic or facts then no amount of logic or facts will change their mind. At best, we can provide a light for people who aren’t already dogmatically committed to creationism.


How can you possibly know that? Some laypersons, certainly.

Who is this collective “the layperson”? I think you may be overgeneralizing from your own views.

Might I suggest that the example doesn’t have to be about symbiosis? All that’s necessary is an example of selectable genetic variation for any trait. Traits involved in symbiosis are not in any way unique or special.

Because those offering such responses are willing to test such hypotheses.

Not if we’re discussing plausibility. Also, for virtually every trait that has been studied in biology, individuals vary and some of that variability is heritable. That’s real evidence that the creationist ignores, often quite deliberately.

Strictly speaking, it would be an allele of a gene, not a gene. Even more likely, it would be a complex epistatic phenomenon produced by alleles of multiple genes that yields a far more simple distribution of preferences.

Am I a layperson? (On the one hand my degree is in Physics, worked as a computer programmer, and have no formal qualifications in Biology, not even at high school level. On the other hand I am an amateur botanist and my name is mentioned a few score times in the botanical literature.)

You could be a semi-layperson if you want.

Some days I wonder why in the world I ever suggest anything at all here. This being one of them.

You are correct. I do not know all laypersons.

Yes, I was purposefully overgeneralizing.

Certainly, do it that way. I suppose that every layperson (I know all except for the semi-laypersons like @Robert, below ) who knows so little about biology that they continually make arguments from incredulity would make the leap from symbiosis to any old genetic variant.

As John Harshman would say, “How can you possibly know that?”

Many people who have misunderstandings in this regard are able to come here to read about and see the many examples of transitional fossils that have been provided here, in the comments regarding these topics. Do you think that they have no effect?

Another common misunderstanding is regarding the Cambrian “explosion.” Recent findings articulated here and elsewhere do a great service in clearing up this misconception. Another waste of time?

Symbiosis is one of those icons of evolution that is easy to understand. I merely pointed out that it would be better understood by all if the purported evolutionary pathway was backed up by data. Silly me.

What sort of data would back it up? That isn’t clear to me.