googlef87758e9b6df9bec.html A Sure Word: How Unique Does It Have To Be?

Tuesday, May 15, 2012

How Unique Does It Have To Be?

One of the most cited articles published on TalkOrigins (TO) is their 29+ Evidences For Macroevolution. One evidence cited among the 29 is the much touted “nested hierarchy of species.” The so-called “nested hierarchy” is a sort of feather in the evolutionary cap. It is sometimes invoked as a sort of proof of evolution (of course, nothing is science can really ever be “proven”). If all species are descended from a common ancestor, they should be able to be arranged into a type of hierarchy. It's a prediction of the theory of evolution. TO believes the hierarchy is observed and thus the prediction is confirmed. From their article we read, Most existing species can be organized rather easily in a nested hierarchical classification. This is evident in the use of the Linnaean classification scheme. Based on shared derived characters, closely related organisms can be placed in one group (such as a genus), several genera can be grouped together into one family, several families can be grouped together into an order, etc.”

A good scientific theory should be falsifiable. TO knows this and so, with each prediction they make, they include a potential falsification. In the case of the nested hierarchy, TO admits that it would be problematic for evolution if “many species” were found that were difficult to group in the hierarchy. By saying “many species,” TO seems to hedge their bets against any single species being found that could potentially upset the whole theory. Yet in their article they say, “Keep in mind that about 1.5 million species are known currently, and that the majority of these species has been discovered since Darwin first stated his hypothesis of common ancestry. Even so, they all have fit the correct hierarchical pattern within the error of our methods. Furthermore, it is estimated that only 1 to 10% of all living species has even been catalogued, let alone studied in detail. New species discoveries pour in daily, and each one is a test of the theory of common descent [bold added]. TO would like to give the impression that even a single new species could disprove the whole theory. It's a bold move designed to imply that the theory is so robust that it stands unflinching every day while each new species discovered confirms evolution to be true.

So let me ask: how unique would a new species have to be in order to disprove the entire theory of common descent? Science Daily just published an article describing a new species which, after genetic analysis, is “not a fungus, alga, parasite, plant or animal.” That's curious. Exactly where does it fit in the nested hierarchy, then? The article says, “We have found an unknown branch of the tree of life [aka nested hierarchy] that lives in this lake. It is unique!”

Exactly how unique is this creature? From the article, we read, “We are surprised. Enormous quantities of environmental samples are taken all over the world. We have searched for the species in every existing DNA database, but have only found a partial match with a gene sequence in Tibet. So it is conceivable that only a few other species exist in this family branch of the tree of life.”

TO said that every new species discovered “is a test to the theory of common descent.” Since this creature cannot be placed on any existing branch of the “tree of life,” wouldn't it be the magic bullet which TO said would falsify the theory? Alas, no. Even though TO said their theory is tested with each new species discovered, they really don't mean to say that a single species – no matter how unique – would undo all those nested hierarchies they've spent all this time drawing. What they've done instead is simply draw a new branch on the tree of life from this species directly to the imagined common ancestor.

What we have is a vicious cycle of circular reasoning. Scientists are already convinced their theory is true and so their theory isn't tested by any new evidence. Instead, all new evidence is viewed in light of the theory. The nested hierarchy isn't at all threatened by the discovery of new species so long as scientists fearlessly draw new branches to accommodate them. What's laughable is that they use their theory to draw the “tree of life” and then have the nerve to hold up the “tree of life” as evidence for their theory!


Steven J. said...

A couple of points:

First, a "test" is not necessarily a falsifier (a reasonable analogy, I think: if you fail a pop quiz in a class, you don't necessarily fail the course, but your chances of passing it go down). Quine and Duhem argued, separately, decades ago that no "silver bullet" falsifier could exist for any theory, since you can't test hypotheses singly: every test is a test of multiple hypotheses (e.g. if I test the hypotheses "acid X will dissolve substance Y," I'm testing not only that hypothesis, but the hypothesis that the chemicals in front of me are in fact X and Y). Any theory can be rescued from an apparent falsification by appropriate auxiliary hypotheses.

Second, I do not see that it is an implication of the theory of evolution that we have uncovered every living branch of the tree of life. A centaur is a violation of the nested hierarchy, since it fits in in two separate places. So would, e.g. bats with feathers, birds with mammary glands, or snakes with one bone in the lower jaw and three in the middle ear. But a previously undiscovered single-celled eukaryote? It fits in on its own, previously undiscovered branch. Some branches are to all appearances extinct (e.g. sauropod dinosaurs, conodontophores, graptolites, etc.). Some branches perhaps were never very diverse. Some perhaps were once diverse but are now nearly extinct (that seems to be the best guess for this one).

It does fit in the nested hierarchy: it is a eukaryote (admittedly a very high-level branch of the tree of life, but still, it unambiguously groups with us and pine trees, not with bacteria or archae), and the quoted researchers believe it to be a primitive form resembling species at the root of the eukaryote (superkingdom) tree.

Oh, and the "tree of life" was first drawn up by Carolus Linnaeus, a creationist botanist, in the 18th century. It has been modified many times since then, but the basic tree pattern remains -- and can be derived without reference to the theory of evolution (see "pattern cladism"). It was not invented by evolutionists; its existence was one of the data that evolutionary theory was devised to explain.

RKBentley said...

Steven J,

It was TO that made the claim that each new species discovered “is a test of the theory of common descent.” Furthermore, they made the statement under the paragraph heading of, “Potential Falsification.” Now, I know there really is no satisfactory test that could possibly disprove evolution but if TO wants to pretend it's a robust theory that could potentially be falsified, then I'm going to press the issue with them.

You're right, of course, that understanding the theory of evolution doesn't automatically mean we can predict every branch on the tree of life. There could be many yet-to-be-discovered species that are completely unlike anything we've discovered before. Yet no matter how alien any new species might be, it's not really a test of evolution so I don't really take TO's “test” seriously. Think about this: even if we found a species THAT DID NOT POSSESS DNA, it still wouldn't falsify evolution for evolution does not demand that life arose only once on earth. There could be a second tree of life with a completely different root. Such a second tree might disprove “common descent” of all species but isn't proof against dino-to-bird or ape-to-man evolution.

I did read the article on Science Daily so I am aware the critter in question is a eukaryote. Still, I asked the question, “how unique does it have to be” before it becomes a true test of the theory? TO said that every new species discovered is a test of the theory of common descent. I would say any creature that possesses DNA could be put somewhere on the tree of life – even if scientists have to continuously draw new branches. So how rigorous is this test, really?

Finally, I am also aware that Linnaeus was a creationist. TO had used the term “nested hierarchy of species” (actually, many evos like to use the term “twin nested hierarchy”) and Science Daily used the term “tree of life.” I wanted to be sure people understood we're talking about the same thing. I'm pretty sure I have discussed on my blog before that a nested hierarchy is observed in nature but it's not “proof” of evolution.

I found this comment I made to The Paleobabbler, 11/10/2010: “The ability to group animals into a nested hierarchy could be explained by common ancestry but I'm puzzled why you think it's a problem for creationists. Did it occur to you that created things could also be grouped into nested hierarchies? If I had a bucket full of needles, pins, screws, staples, nails, and other assorted fasteners, all of various sizes, I suppose I could arrange them into nested hierarchy or draw some imagined family tree.” (You replied to that comment, BTW).

That species can be grouped into a hierarchy only proves that species can be grouped into a hierarchy. Linnaeus was able to identify the similarities between groups of creatures without assuming an evolutionary relatedness.

Thanks for visiting. God bless!!


Steven J. said...

Any suite of entities can be grouped into a hierarchy. Anyone who's ever outlined a topic for a school class has constructed a nested hierarchy; anyone who's shopped at a department store has seen a nested hierarchy set out in two (or three) dimensional space. The Dewey Decimal system is a nested hierarchy. Note, though, that there are books that can be filed under multiple numbers in the Dewey Decimal system (is a history of the great plague "epidemiology" or "history?" -- I've seen two copies of the same book filed in different sections of the same library). If you use different criteria for sorting, you get different hierarchies. The odd thing about biology is that you can use different criteria and get very, very similar trees (and the occasional differences can be chalked up to convergent evolution or genetic drift). Given that special creation ought to be able to, e.g. re-use feathers for all flying vertebrates or equip pandas with primate-style thumbs if they need thumbs, this calls for an explanation: "common descent with opportunistic modification" is an explanation; "divine whim" is a possibility but not an explanation, since it does not explain why things are this way rather than some other way.

Note that a single tree of life is implied by universal common descent. A form of life that didn't fit in anywhere in the tree of life would not, by itself, argue against evolution but against a single origin of existing life; it would mean at least two separate abiogenesis events (note that evolutionary theory doesn't automatically imply universal common descent, though thus far it appears that universal common descent is the case). The implied "test" provided by a new species is whether it fits into multiple places in the tree of life, or fits in in some ways but not in others. An example would be something that looked for all the world like a rodent or monkey, but had radically different biochemistry from mammals, or chordates in general (e.g. for all Star Trek's endorsement of evolution, Mr. Spock was a walking argument for special creation).

RKBentley said...

Steven J,

The thing that I've noticed about the tree of life, is that it's not as black and white as most evos would have us believe. How many times have I read that some new discovery “redraws the tree of life”? A few years back, I wrote a post about another Science Daily article that was headlined, “Huge Genome-scale Phylogenetic Study Of Birds Rewrites Evolutionary Tree-of-life.” So even though TO and others would have us believe the nested hierarchy practically writes itself, there are more than a few examples of species that have to be moved around.

Your example of Mr. Spock is very interesting. Did you think of that? It doesn't matter because it's very clever regardless. I would there are real world examples of the very thing you're talking about. Marsupial moles, for example, are astonishingly similar to placental moles. Wikipedia invokes “convergent evolution” to explain the similarities. If form follows function, then convergent evolution sounds plausible; but if that's so, then the Mr. Spock similarity could be just as easily explained. What you say is a “walking argument for special creation” could also be explained by convergent evolution. We might say it's the same evidence but different explanations. Wait... haven't I've heard that somewhere before?!

Thanks for your comments. God bless!!


Steven J. said...

As the Science Daily article notes, bird taxonomy is notoriously difficult, although the usual reason cited is less "explosive radiation" in the late Cretaceous as the severe constraints placed on bird anatomy by the need of most bird groups to fly: they all have to look a lot alike (and adaptions to predation, or life on the water, etc. impose their own demands atop these already stringent constraints). The study established unexpected connections between some bird orders. For example, finding that parrots were a sister group to perching birds was a surprise, but it overturned no previous assumptions, since there were very few ideas about how the various bird orders were related to one another, beyond all being birds. Finding that some orders had to be split up was a bigger shock (e.g. that falcons are not, in fact, raptors like eagles and hawks), but again, being a predatory flyer puts severe constraints on structure and makes convergent pressures greater.

As for Mr. Spock, he has, according to Star Trek, green blood and a strikingly different blood chemistry from humans (given that all vertebrates have red blood, this would imply that he is at least a different phylum from his crewmates); this makes his resemblance to us less like the resemblance of marsupial moles to placental moles (both, after are, are already mammals, and of course already synapsids, amniotes, tetrapods, etc. -- they have to build on the same underlying anatomy for the same basic lifestyle; the same of course applies with equal or greater force to convergences among bird groups -- but more as if we'd noticed that a species of octopus could be mistaken at first glance for a dolphin.