It’s curious how adaptations that could have evolved by natural selection are nevertheless seen as evidence for Intelligent Design. Indeed, in the case of diarrhea and the appendix, as ID advocate David Klinghoffer maintains in the article below from Evolution News (click on screenshot), the evidence is not just an adaptation itself, evincing the wisdom of the creator, but supposed foresight: designing a feature in advance before it would be needed—something that natural selection couldn’t do. Unfortunately the article and associated video doesn’t show any such thing, nor does it show that ID is a more parsimonious explanation for diarrhea and the functionality of the appendix than is evolution.
Klinghoffer’s piece is about a recent book by Marcos Eberlin, a Brazilian chemist at the University of Campinas. (His Wikipedia entry states that “Eberlin is an advocate of intelligent design in Brazil, a pseudoscience on which he also lectures and he has signed the Dissent From Darwinism statement. He is a creationist also, and have said that evolution theory is a fallacy.”)
So here are both Klinghoffer and Eberlin implying that that the Great Designer solves problems before they come up. Klinghoffer’s blurb:
In his new book, Foresight, Dr. Eberlin develops a case for ID from the observation that so much in life and in nature appears to have been designed with a view to anticipating future problems and solving them ahead of time. Only minds can do that. Take the problem of eating adventurously and possibly consuming some bad food. The solution is diarrhea — the body’s “power wash” cycle, as he puts it. “It’s really nice,” he adds. “Diarrhea is a blessing.” You’ve probably never thought of it that way before.
But discomfort aside, the solution itself comes with a problem: it depletes the intestines of necessary microorganisms. The solution to that is the appendix, the supposedly useless, vestigial organ according to Darwinists, which in fact serves as a helpful reservoir of microorganisms.
And here’s Marcos Eberlin showing the creator’s marvelous foresight.
As for appendicitis, Eberlin claims that it’s only a problem in First World countries. I’m not sure if that’s true, and, if it is, why that’s so. Some hypothesize that in countries with less sanitation, the immune system gets used to challenges and there is thus less inflammation of this organ. But the issue is whether the precursor to the appendix was, in net, deleterious in our ancestors, and, if so, that was the reason it shrank.
Let’s see if there’s good evidence for design here. First of all, diarrhea may well be a body’s way of flushing out toxic substances and microbes from the gut. There’s no problem with that evolving by natural selection, and this has been recognized by advocates of Darwinian medicine for a long time, as in the article below by Randolph Nesse (click on screenshot). I’m not sure that we know that diarrhea is an adaptation rather than an unevolved reaction of the gut, but at least there’s no barrier to seeing how a body’s expulsion of noxious substances could have been adaptive.
It’s also possible that the appendix serves as a reservoir of healthy gut bacteria to repopulate the intestine if it’s purged of its normal microbiome by something like diarrhea. This, too, has been suggested before, as in this paper in mbio six years ago. That paper proposes that “normal” gut bacteria are protected from purging by residing in a biofilm in the appendix, and then can reinvade the gut with healthy bacteria.
So it’s possible, and maybe even likely, that in general having an appendix is actually adaptive: you can repopulate your gut more easily with good bacteria if you have an appendix. And the “downside” of having an appendix—inflammation and death before it was possible to surgically remove it—may not have been something our ancestors faced often.
The question remains, however, whether the appendix is a vestigial organ—whether it is the remnant of a caecal pouch for digestion found in some of our relatives (some herbivores have pouches rather than an appendix). The important thing here is that vestigial organs can assume a new function. Despite that function, organs like the appendix could still be reduced remnants of a feature that once had a different (and useful) function, and thus, despite their new function, still serve as evidence for evolution. (There are, of course, many vestigial features that have no known function at all, like the muscles in human ears that can move them about or the “snake limbs” pictured below.)
It is one of the most common misconceptions about evolutionary morphology that to be vestigial, an organ cannot have a function. That’s not true: all that is required is that an organ be a reduced or degenerated remnant of a feature in an ancestor and have lost the function the presumably prompted its original evolution. It can still assume a new function.
One example: the reduced legs of snakes, which were once larger legs in their lizardlike ancestors. The males use these to stroke and stimulate the female during mating. They are clearly vestigial, as we know from both morphological and fossil evidence, but they still have a function.
Here’s a leg from the female of a ball python (Python regius), showing that the external leg is relatively short. (That’s a standard dissecting kit needle probe.) As Greg Mayer said, who provided the picture, “what you’re seeing is a claw; there’s a femur and pelvis inside.” This is clearly a vestigial feature, but it’s functional in males.
We’re not sure whether the appendix is a vestigial organ in the sense I gave above; the jury is still out. But what is absolutely clear is that there is no need to invoke the existence of a Wise Designer to explain both diarrhea and a bacteria-harboring appendix.
It’s entirely possible, for instance, that features of the gut causing diarrhea evolved as an adaptive response to toxins and bad microbes. Under many circumstances, the gut could repopulate itself from natural sources like food or contact with other individuals. But there might then be an additional advantage to those individuals who were able to sequester some of their gut bacteria on a wormlike structure of the gut: the appendix. That would be subsequent evolution by natural selection—no designer needed here, either. The whole sequence: appendix reduction—> evolution of diarrhea response—> co-option of the appendix to serve as a reservoir for “good microbiota”, can evolve by natural selection. And we don’t even need the first step should the human appendix prove not to be vestigial. Regardless of the sequence, no evolutionary “foresight” is needed.
We may not know whether the appendix evolved as a way to enhance microbe repopulation, or was the remnant of a caecal pouch that assumed this function as an adaptive byproduct. Some day we may have to revise our notion that the appendix is a vestigial organ, though I’m not ready to do that. But what is certain is that IDers like Eberlin and Klinghoffer are suffering from an extreme failure of the imagination in saying that diarrhea evinces an Intelligence On High, and that the appendix was put in place in advance to help those individuals who developed diarrhea.