We Don’t Know Everything About Electric Fish

There are six different lineages of so-called “electric fish,” each of which evolved its potential independently and convergently. The most famous of these is the electric eel, though speaking of convergent evolution that species is not actually an eel. The portion of the body that produces the electric field is called the “electric organ,” and appears to be derived from muscle cells, but are quite different from each other. A recent paper in Science – “Genomic basis for the convergent evolution of electric organs” (pdf, press release) – investigating representatives of four of six lineages determined that, despite their differences, the same underlying genetic and cellular processes have been leveraged (or hijacked) in each case.

Nathaniel Jeanson has an article up today about this paper called “Darwin’s ‘Special Difficulty’ Solved?” His conclusion is, if anything, unusually weak, and it’s difficult to know what to make of it. He begins by quote-mining Darwin, a common tactic but one which the ICR doesn’t seem to often resort:

In Darwin’s seminal work On the Origin of Species he identified numerous examples of biological structures that, at first pass, seem very difficult to evolve. He even wrote a chapter titled “Difficulties on Theory” which he began with this wry comment: “Long before having arrived at this part of my work, a crowd of difficulties will have occurred to the reader. Some of them are so grave that to this day I can never reflect on them without being staggered.”

The full quote of course reads:

Long before having arrived at this part of my work, a crowd of difficulties will have occurred to the reader. Some of them are so grave that to this day I can never reflect on them without being staggered; but, to the best of my judgment, the greater number are only apparent, and those that are real are not, I think, fatal to my theory.

(Emphasis added to further highlight omission; all Darwin quotes in this post are from chapter six of On the Origin of Species.) As is well known, Darwin tended to build up the case for the opposition and then knock it down; this allows today’s creationists to selectively quote only the former portion and pretend for a moment that their arguments are not vastly out of date, long since refuted.

Jeanson then says:

One organ in particular that has dodged evolutionary explanation for over 150 years is the electric organ—the organ in fishes that generates electricity under water. Evolving this organ in one single species would pose serious challenges to evolution. But the organ is present in several fish species which, under the ancestry constraints imposed by the evolutionary interpretation of the fossil record, implies that the electric organ would have had to evolve, not once, but multiple times, making the naturalistic origin of this structure all the more implausible.

This is also a common creationist tactic, and one more often used: evolving a feature is extremely difficult/impossible/unlikely (because they said so), and so evolving it multiple times must be even harder (because obviously). An interesting counterpoint to this comes from the cryptic potentiating mutations in Lenski’s famous experiment, which lead to the repeatable evolution of aerobic citrate metabolism in lineages that possess them – it’s almost as if evolving a feature multiple times isn’t that much “harder,” so to speak, than doing it once.

Next, Jeanson quotemines Darwin again:

Darwin recognized this challenge early in his work in 1859. He wrote, “The electric organs of fishes offer another case of special difficulty; it is impossible to conceive by what steps these wondrous organs have been produced.” Nevertheless, he hypothesized a theoretical way over this hurdle: “As Owen and others have remarked, their intimate structure closely resembles that of common muscle.”

In fact, both of those quotes are part of the same sentence, but there’s even more than Jeanson reproduces. The full paragraph reads: (emphasis as before)

One of the gravest is that of neuter insects, which are often very differently constructed from either the males or fertile females; but this case will be treated of in the next chapter. The electric organs of fishes offer another case of special difficulty; it is impossible to conceive by what steps these wondrous organs have been produced; but, as Owen and others have remarked, their intimate structure closely resembles that of common muscle; and as it has lately been shown that Rays have an organ closely analogous to the electric apparatus, and yet do not, as Matteuchi asserts, discharge any electricity, we must own that we are far too ignorant to argue that no transition of any kind is possible.

The observation of a muscle-like structure has been more than confirmed in the years since – the cells are also seen to arise from muscle cells. It seems that in Darwin’s time he could already see an inkling of how the problem might be solved, and he observed that what was known at the time was hardly enough to declare with confidence that it could not have happened. A century and a half later Jeanson is in a much worse position to make that same declaration, and he only half-tries:

Could electric organs have evolved from mere muscle tissue? Since wholesale evolutionary change must ultimately stem from genetic changes, the first step in answering this question is investigating whether the diversity of electric organs could be produced via a common genetic pathway. Since Darwin knew nothing of genetics, he didn’t realize how big this difficulty really is. His ideas—his visualizations—were overly simplistic.

Genetics need not be the “first step” in such an investigation, and in saying so Jeanson erases basically all work before the present. You may also observe that, had Jeanson actually provided the full quote from Darwin above, he might have inadvertently revealed to his readers that Darwin was aware of his ignorance even if he could not contemplate its true magnitude. That evolution has survived the genetic revolution is widely considered a testament to its accuracy, and Jeanson can’t let this be acknowledged.

But it’s important to remember that there are two parts to this story: how the organs evolved, and how it could be that they did so multiple times. Jeanson only wants to talk about the former, but it is the latter that is the focus of the paper. On this second part Darwin wrote:

The electric organs offer another and even more serious difficulty; for they occur in only about a dozen fishes, of which several are widely remote in their affinities. Generally when the same organ appears in several members of the same class, especially if in members having very different habits of life, we may attribute its presence to inheritance from a common ancestor; and its absence in some of the members to its loss through disuse or natural selection. But if the electric organs had been inherited from one ancient progenitor thus provided, we might have expected that all electric fishes would have been specially related to each other. Nor does geology at all lead to the belief that formerly most fishes had electric organs, which most of their modified descendants have lost. The presence of luminous organs in a few insects, belonging to different families and orders, offers a parallel case of difficulty. Other cases could be given; for instance in plants, the very curious contrivance of a mass of pollen-grains, borne on a foot-stalk with a sticky gland at the end, is the same in Orchis and Asclepias, genera almost as remote as possible amongst flowering plants. In all these cases of two very distinct species furnished with apparently the same anomalous organ, it should be observed that, although the general appearance and function of the organ may be the same, yet some fundamental difference can generally be detected. I am inclined to believe that in nearly the same way as two men have sometimes independently hit on the very same invention, so natural selection, working for the good of each being and taking advantage of analogous variations, has sometimes modified in very nearly the same manner two parts in two organic beings, which owe but little of their structure in common to inheritance from the same ancestor.

The recent results amount to a confirmation of this concept, and more. But instead of talking about this Jeanson… makes another quotemine, as it turns out:

Realistically, the question of whether these organs originated via evolution does not rest on the commonality or differences among the electric organs’ genetic programs. Darwin did not cite developmental similarity as the gold standard test of evolution. Instead, in his “Difficulties with Theory” chapter he said, “If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down.” As Michael Behe has pointed out, this test can be taken only at the molecular level. Conversely, as Behe also highlighted, evolution is a failure if an organ—such as the electric organ—relies on mutually interdependent (irreducibly complex) molecular parts for its function.

The full Darwin quote is, of course:

If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find out no such case. No doubt many organs exist of which we do not know the transitional grades, more especially if we look to much-isolated species, round which, according to my theory, there has been much extinction. Or again, if we look to an organ common to all the members of a large class, for in this latter case the organ must have been first formed at an extremely remote period, since which all the many members of the class have been developed; and in order to discover the early transitional grades through which the organ has passed, we should have to look to very ancient ancestral forms, long since become extinct.

The creationists – the “intelligent design proponents” especially – have conflated this with their “irreducible complexity,” a much less stringent designation. Indeed, Darwin begins his next paragraph by saying that “We should be extremely cautious in concluding that an organ could not have been formed by transitional gradations of some kind.” Jeanson has no basis in his own conclusion, but that’s not about to stop him.

He also declares that this is some kind of “gold standard test,” which apparently means that other considerations can be conveniently be discarded. In fact Darwin uses similar language to the above elsewhere:

If it could be proved that any part of the structure of any one species had been formed for the exclusive good of another species, it would annihilate my theory, for such could not have been produced through natural selection. Although many statements may be found in works on natural history to this effect, I cannot find even one which seems to me of any weight. It is admitted that the rattlesnake has a poison-fang for its own defence and for the destruction of its prey; but some authors suppose that at the same time this snake is furnished with a rattle for its own injury, namely, to warn its prey to escape. I would almost as soon believe that the cat curls the end of its tail when preparing to spring, in order to warn the doomed mouse. But I have not space here to enter on this and other such cases.

Creationists do point to altruism as evidence against evolution – though I’m yet to see a solid example that would apply here – but it’s quite clear that these tests do not have the status that Jeanson affords them. It may be that if some structure could be found that truly meets them evolution would be disproved, but that tells us nothing about how to prove evolution. That part Jeanson is ignoring, as it’s not going away – all he has is the long-shot possibility of a disproof.

With that in mind, he concludes:

To date, no one has comprehensively identified the relationships among the molecular components undergirding electric organ function. Until these relationships are elucidated, the plausibility of the evolutionary origin of these structures remains purely speculative and claims of evolutionary “fact” must be rejected because they are without scientific support.

In other words, because we don’t know everything about how these organs function Jeanson considers himself able to pretend that it didn’t happen. But remember what Darwin said (and Jeanson omitted): we certainly don’t have the evidence that would tell us that it didn’t evolve, quite the contrary. And anyway, as we learn more about the complexities of the process the ICR is only going to say that this means things are only more difficult, and that what was thought before was “overly simplistic.”

It is the creationist way.