How a Darwinist Explains “Living Fossils”

first_imgDarwinism is a flexible concept that must embrace a wide variety of observations, from apparently fast-evolving plants (see 10/12/2004 item on maize) to organisms that seem to remain unevolved for eons.2  Darwin himself saw this flexibility as a strength for his unifying concept of common descent; others criticized it as rationalization (i.e., a concept that can explain anything explains nothing).  Take the case of so-called “living fossils,” organisms whose modern counterparts are virtually identical to fossils sometimes hundreds of millions of years old.  If a land animal could evolve into a whale in 50 million years, for instance, why would a horseshoe crab show no change at all for 10 times as long, 500 million years? (see 06/21/2002 headline).  How can the fluidity of constant evolutionary change over time be reconciled with observations that many different kinds of creatures – trees, salamanders, ostracods, reptiles, insects and fish – have apparently not evolved at all?    This subject was recently tackled by Lee Hsiang Liow of the Committee on Evolutionary Biology at the University of Chicago.  Examining fossil crinoids (branch-like echinoderms that attach to the seafloor, also called sea lilies and feather stars), Liow tested “Simpson’s Rule” of “the survival of the relatively unspecialized,” a rule George Gaylord Simpson proposed in 1944 as an explanation for living fossils and long-lived taxa.  Basically, it suggests that specialists evolve, but generalists persist.  Liow applied the rule to crinoids and published the results in American Naturalist.1  She studied 1,195 species, representing 752 genera, and concluded that long-lived crinoid genera seem relatively unspecialized, in accordance with Simpson’s Rule, but the reverse is true for higher taxa.  The conclusion seems to raise doubts about the utility of Darwinian explanations.Prolonged stasis in a world of change is a puzzling biological phenomenon.  Extremely long-lived or geologically long-ranging taxa have been a popular subject of discussion for paleontologists and neontologists alike ever since Darwin ([1859] 1964) coined the term “living fossils.”….Whether it is called bradytely, arrested evolution, morphological stasis, long-lived taxa or something else, or whether “living fossils” are dubbed paradoxical, relictual, primitive or specialized, the phenomenon of stasis has rarely been studied in a quantitative manner.  This Liow set out to correct, at least in the case of crinoid evolution.  The crinoid class is ideal for study because it span much of the geological column and contains many well-characterized examples, both fossil and living.  She compared samples and deduced a morphological average, then tried to determine if longevity was a function of “bizarreness.” Simpson implicitly took a comparative approach when he wrote about the “rule of the survival of the relatively unspecialized” (1944, p. 143).  He thought that unspecialized subgroups of a clade seem to persist for longer periods of geologic time but did not explicitly define “specialization.”  Here, I quantify specialization by comparing individual morphologies to a group mean; the closer a morphology is to a group mean, the less specialized it is.  I ask whether long-lived genera … in any given crinoid order occupy regions of morphospace that are random with respect to the mean morphology of that order.  Could survival be correlated with morphological bizarreness or a deviant morphology …?  Or would long-lived genera have morphologies close to the mean morphology…?The short answer is: Simpson seems to be right on one level.  “I find that the morphologies of long-lived crinoid genera are, in general, closer to mean morphologies than shorter-lived genera in the same order.”  But when higher taxonomic categories are examined, the rule fails:Similarly, but from a completely different conceptual perspective, I ask whether long-lived crinoid genera in any given crinoid higher taxon (e.g., suborder, order) occupy regions of morphospace that are random with respect to a basal morphology of that higher taxon.  I find that mean morphological distances of long-lived genera from basal morphologies are seldom distinct from those of their shorter-lived relatives.In other words, she found a contradiction in the trend between lower and higher taxonomic groups.  Part of the problem is the fuzziness of the evolutionary record:There is no available phylogenetic framework for comparing rates of character transformation in the global pool of fossil crinoids.  Likewise, there are no detailed samples of crinoid lineages in a stratigraphic column for investigating character reversals, convergence, or the lack thereof.Nevertheless, she found a way to compare features: “The morphological characters used here are not assumed to be strictly homologous but are assumed to reflect only general fossilizable morphology determined consistently within the crinoid bauplan [body plan].”  Also, the fossil history was determined from location in the geological column, both first and last appearance (see 05/21/2004 headline), and when dealing with fossils, the classification into genus and species is not always clear cut.  Geological history adds to the confusion:Just as in previous analyses when genera are grouped according to orders, genera in each period are mostly short lived.  However, rarefied samples of shorter-lived genera through each period inform us that the long-lived taxa can be more, less, or equally deviant compared with shorter-lived taxa of an equivalent sample size (table C2).    Genera that are extremely long lived within each order are also more likely … than other genera in the database to have passed through one or more mass extinctions even though passing through mass extinctions does not necessarily ensure persistence.I.e., the longer you live, the more dangers you have faced, but facing dangers doesn’t make you Supercrinoid.  She claims, nevertheless, that “the likelihood of the occurrence of ‘living fossils’ or long-lived taxa increases with time,” a truism given the evolutionary and geological-time assumptions.    Liow addresses more factors that confuse the picture and could bias the results, such as taxonomic lumping, limited range of some species, the tendency for long-lived species to swamp short-lived ones, “issues of stratigraphic resolution of age dating,” and disagreement over how to define a “long-lived” taxon.  This discussion seems intended to cushion the next paragraph, the conclusions.  Before opening the curtain, she cautions, “In summary, longevity is relative and dependent on taxonomic inclusiveness.  These important axioms are often neglected in articles that address extreme persistence or morphological conservatism.”    Conclusion time.  What can be claimed based on this detailed analysis of crinoids?“First, most taxa (genera and families) are short lived and ‘average”…. which implies that experiments in morphology are usually not long lived.”  This seems to suggest Mother Nature is a bumbling tinkerer.“Second, long-lived genera within orders are often less morphologically deviant or less specialized than expected when compared with rarefied samples of corresponding shorter-lived genera.”  This was apparently a big surprise.  “In other words, long-lived genera are not only not unusual, some are unusually average!” (exclamation in the original).“Third, patterns of morphological deviations from basal morphologies versus durations are unclear.”  Enough said.Fourth, there appears to be an increase in long-lived groups through time, but this appears to be an artifact of the assumptions of phylogeny and geologic ages.“Fifth, taxonomic ranks and inclusiveness of higher taxa are critical factors when discussing longevity because identities of long-lived taxa may dramatically change according to these factors.”  This suggests that previous investigators failed to see the big picture.“Last, identities of long-lived taxa may change with respect to which definitions of longevity are used.  This may or may not (as was the case for this article) change conclusions being drawn on long-lived taxa.”  This seems to say that conclusions are a function of definitions, not data.She lists a few suggestions that have been offered for why some species persist.  Maybe “extinctions are not biologically random,” for instance.  Overall, though, she is confident that “Based on the results of the current study, I rule out the idea that long-lived genera are morphologically deviant or unusual when compared within the realm of an order.”  This seems to say, “Simpson was wrong” at higher taxonomic levels.    What are more instructive in this paper are the zingers in the last paragraph:There are of course many unanswered questions.  This study focused on persistence, but there is no available information on actual rate of character evolution.  Do long-lived taxa experience rapid rates of character reversals or zig-zag evolution (Henningsmoen 1957), such that apparent persistence is only a sampling artifact, or does persistence necessarily mean slow change or cryptic change (Knowlton 2000)?  …. To remain similar enough to an ancestor so a lineage retains a single taxonomic identity requires whole chains of more or less identical events (Gingerich 2001), but what causes these identical developmental events to occur generation after generation?  What relative proportions do ecology, biogeography, morphology, and phylogenetic inertia contribute to longevity?  Patterns and statistical correlations do not imply causation; tests using techniques from fields ranging from paleontology and phylogenetics to molecular biology and genetics need to be designed to investigate the existence and workings of mechanisms that promote longevity.Go to the top of the paper.  Infinite loop.1Lee Hsiang Liow, “A Test of Simpson’s ‘Rule of the Survival of the Relatively Unspecialized’ Using Fossil Crinoids,” The American Naturalist 2004, Vol. 164, pp. 431-443, University of Chicago, 0003-0147/2004/16404-40222.2For examples, see previous headlines about coelacanth fish, pine trees, horseshoe crabs, tuatara reptiles, salamanders, bacteria, protozoa and termites, and butterflies.Every word of this long paper was scrutinized for a hint, somewhere, of an explanation for living fossils.  It was like taking a long, hard hike with a confused guide and at the end of the day finding yourself right back where you started, and on top of that, finding out that your destination was much farther off than you first expected.  Nothing in this paper was any help to the Darwinites.  Simpson’s Rule was tested and found wanting.  The number of variables outnumbered the constants, and the validity of any formula was questionable to begin with.  There is no reason to suspect that fragile little sea lilies would outlive dinosaurs through mass extinctions, and there was nothing within the known diversity of crinoid classes to predict why some would last long and others would disappear quickly.    This is not to pick on Dr. Liow.  After all, she meant well and tried to be scientifically rigorous, at least more so than predecessors who relied on comparative rather than quantitative methods.  She did her homework and referred to all the prior literature on this subject.  And she is, after all, an expert, being on the Committee on Evolutionary Biology at the University of Chicago.  But in the end, it didn’t matter; the doubts swamped the claims.  Just when we were about to give her credit for finding at least half a trend, she let loose with a barrage of major questions that cast doubt on the validity of any evolutionary explanation for living fossils.  Notice also that her subject was not a minor matter.  The debate about stasis is a major issue that bears on the very heart of evolutionary theory.  If the Darwin Party cannot explain how things change or how things stay the same, then they cannot explain anything.    Notice what she admitted in that last paragraph: there is no available information on actual rate of character evolution, she said, and she’s not restricting that statement to crinoids.  In lieu of explanations, she tosses out alternative plot lines and made-up concepts, like “zig-zag evolution” and “cryptic change” and other head-scratchers, then unloads a dump truck load of devastating statements that say, in effect, that Darwinists don’t know anything.  She just hopes that some day, somebody else will figure it out.  From our experience, this paper was not an isolated case.  The more in depth evolutionary theorists try to support their hunches with evidence, the more trouble they find.    Evolutionary explanations are like hot potatoes.  The Darwin Party brags about how many players are in the game and how many potatoes are being tossed around, but there is no potato anyone wants to hold onto and eat.  Dr. Liow held it long enough to decide that, “yes, it is hot,” then tossed it to someone else.  This game goes on and on in the literature while Eugenie Scott and the other Darwinite salespeople speak of this frenetic activity as if a healthy meal of science is being cooked up.  We’re tired of waiting.  When do we get served, and how do we know the spuds are even palatable?  The ones we have glimpsed so far are pretty gross.  No amount of heat will fix a rotten potato.(Visited 21 times, 1 visits today)FacebookTwitterPinterestSave分享0last_img

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