Sunday, January 29, 2012

Evolution of Horseshoe Crabs

 
The IDiots are at it again but this time they are aided and abetted by scientists who should know better. The subject is horseshoe crabs, famous as "living fossils" because species that look similar to the four living species were around millions of years ago.

The BBC (United Kingdom) is broadcasting a new television series called "Survivors"1 staring this month. The first episode is Horseshoe crabs are one of nature’s great survivors. The show is based on a book by Richard Fortey of the Natural History Museum in London, England.

Here's a quotation from the BBC press release where Fortey attempts to explain why horseshoe crabs haven't evolved.
A strange evolution?

Evolution not only brings about ‘improvements’ in body shapes and design that help a species adapt better to its surroundings. It also allows some species to remain basically the same.

‘These creatures tell us that evolution does not move inevitably forwards towards new morphology and new designs,' comments Fortey.

'Evidence for evolution is also found in past designs that endure to the present day. As long as the right habitat endures, then so will some of the creatures that inhabited the distant past.
Think about it for a moment. What Fortey is saying is that no change is "evidence" for evolution! I suppose he could be talking about negative selection and that's probably what he was thinking about in the context of the interview. It's still a silly thing to say and, just as you might have predicted, the creationists have jumped all over it.

First, there's Turning an Unevolved Horseshoe Crab Into a Darwin Showpiece.
Articles like this are more evidence that once the level of public credulity is sufficiently reduced by accurate information about the logical tricks of evolutionists, people will laugh Darwin off the stage of history and wonder how on earth so many smart people fell for his view of the world.

Let’s review what we were just told.

• Complex designs just popped into existence without ancestors.

• These designs were not only complex, they were better at surviving than more than 90% of other animals that followed.

• They endured virtually unchanged for 450 million years.

• Evolution improves body designs, but it also allows them to remain basically the same.

• A past design that endures to the present day constitutes evidence for evolution.

If you are sufficiently dumbfounded at these shenanigans committed in the name of science, stop taking it. Fight back. Demand logic. Demand integrity. Call a spade a spade. This spadeful of nonsense calls for a ultrasaurus-size pooper scooper.
Then there's Denyse O'Leary: Darwinist: Evolution and no evolution are the same thing, it turns out. She laps this stuff up without giving a second thought to the logical inconsistency of rejecting 99.9% of the fossil evidence while promoting the 0.1% of it that seems to cause a problem for "Darwinism." She thinks that's okay because any "problem" for evolution is evidence that God exists.

Here's the real problem. Evolution cannot be stopped no matter how hard you try. There are four species of horseshoe crabs alive today and scientists have no trouble telling them apart. Furthermore, scientists are quite capable of distinguishing the modern horseshoe crabs from the various fossil species. Thus, it is not true that the morphology of horseshoe crab species has not changed in millions of years.

But there's more. Sandwalk readers will know what's coming.

Evolution is not just adaptation and it's not just visible morphological change. It includes things like adaptation at the molecular level and also the fixation of nearly neutral alleles by random genetic drift. You cannot stop evolution unless you stop mutations from happening and you prevent drift. That's not possible so it's not possible that a "living fossil" hasn't evolved. The best you could say is that for some clades the rate of visible morphological change is slower than in some other lineages.

Checking PubMed reveals dozens of papers on the evolution of horseshoe crabs. The latest I could find is Kamaruzzaman et al. (2011). These authors are interested in the relationship between the extant species of horseshoe crab and their relationship to other arthropods. Here's their tree based on the cytochrome C oxidase I (COXI) gene.

Look at that! Not only are They are able to show that the four modern species evolved from a common ancestor several million years ago. they are also showing that horseshoe crabs are more closely related to insects than they are to common crabs. There's just as much evolution on the lineage leading to horseshoe crabs as on all the other lineages. And that's just what we expect, once we understand evolution.

Please, let's stop this silly myth that "living fossils" have not evolved for millions of years. It's totally inconsistent with everything we know about evolution and it's flatly contradicted by the evidence. We may not be able to correct the creationists but surely we can educate our fellow scientists so they don't make fools of themselves in public?




1. This is British. You can be sure that the pun/irony is intended.

Photo Credit: Horseshoe crab: Bronx Bohemian.

Kamaruzzaman, B.Y., Akbar John, B., Zaleha, K. and Jalal, K.C.A. (2011) Molecular Phylogeny of Horseshoe Crab. Asian Journal of Biotechnology, 3: 302-309. [doi: 10.3923/ajbkr.2011.302.309] [Science Alert]

16 comments:

  1. Jeez - I am just a lowly assistant professor at a community college and even I understand enough to have corrected students (and faculty) when they say that horseshoe crabs have not evolved.

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  2. Isn't the existence of a species who can maintain a relatively static appearance in the the face of slowly changing environmental pressures an argument *for* evolution? I mean, the species, while almost static, is not 100% static. If it were, any slight change in environmental conditions would have led to its disappearance. And for species as old as the Horseshoe Crab, that would imply that environmental conditions could not have changed at all over the 450 million years they have existed. That is simply too laughable a prediction of the ID position to be taken seriously.

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  3. I am not a biologist but I was almost shouting at the TV screen when I heard Prof Fortey making the comments illustrated by the press release.

    I assumed that in later episodes he will be explaining the genetics of how some species appear to retain the morphology of precursor species - or rather how their dna has evolved despite the contrary indications of a lazy and careless glance at the external morphology. We shall see.

    Creationists have always used the discovery of a living coelacanth to make the same argument.

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  4. Peripheral point, but I'm suspicious of one of the results you point out, that horseshoe crabs are closer to insects than to true crabs. There's a lot of data to suggest that this is not true, and that in fact insects are nested within crustaceans, but horseshoe crabs most certainly are not. I hope the publication didn't trumpet that result, which is supported at only 68% (bootstrap percentage, I suppose?). Most data show that the classical impression is correct, i.e. that horseshoe crabs are most closely related to scorpions, of the few taxa sampled. If I were looking for relationships, I wouldn't use COI or a tiny and apparently oddly biased sample of arthropod diversity. This tree nicely tests the relationships among horseshoe crabs, though.

    Still, your point, that horseshoe crabs certainly are not stationary when it comes to molecular evolution, remains.

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  5. That phylogeny from the Kamaruzzaman et al. paper looks wrong. Horseshoe crabs have always been considered to be chelicerates, more closely related to arachnids, and insects more closely related to crustaceans than to horseshoe crabs.

    Also, note:
    * The 1970 paper by Selander, Suh and Lewontin in Evolution where they asked whether there was less molecular variation in these "living fossils" than in other species -- there wasn't.
    * A study by Bruce Riska in 1981 in Evolution on the same issue measuring morphological variation.

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  6. But it's a tree of cytochrome C, not a tree of horseshoe crabs, insects, and crabs. It's a tree of a single tree, it can vary from our overall understanding of phylogeny and still be technically correct. It just shows that a single gene isn't super informative, no?

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    1. I think you are conflating two possibilities here:

      1. The tree is right for cytochrome c but not for the species. That can happen if polymorphisms are maintained over a long period or it there's horizontal transfer.

      2. The tree is wrong just because a short sequence can't be all that reliable as a guide to phylogeny.

      Either is possible. But given the probable lengths of time a polymorphism would have to be maintained to make 1 the answer, I'm suspecting that 2 explains the situation better. Mitochondria, in fact, have shorter expected durations for polymorphism than do nuclear autosomal genes.

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  7. Crevo - the website of disgraced JPL tech David Coppedge. Not to worry - he once wrote that phylogenetic analyses "have" Maximum Likelihood and that heuristic searches are "just guesses."

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  8. I think I could make a pretty good argument that dense o'leary is closely related to toxic sludge, and that neither she nor the rest of her IDiotic ilk have evolved and acquired any new, positive, intellectual traits for thousands of years. They're as brain-petrified as their primitive, superstitious ancestors. Living fossils may be a good term to describe IDiots.

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  9. Something I don'd understand at all: If one compares insects, malacostraca, scorpions and xiphosura, how can a branchiopod (Artemia franciscana) be used as "outgroup"? This thing should be closer to the insects than anything else in the study.

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  10. Just the abstract shows many bizarre features, and I don't just mean the broken English:

    "Abstract: An effort to assess the utility of 650 bp Cytochrome C oxidase subunit I (DNA barcode) gene in delineating the members horseshoe crabs (Family: xiphosura) with closely related sister taxa was made. A total of 33 sequences were extracted from National Center for Biotechnological Information (NCBI) which include horseshoe crabs (Class: Merostomata), beetles (Class: Insecta), common crabs (Class: Melacostraca) and scorpion (Class: Arachnida) sequences. Constructed phylogram through comprehensive dry lab methodology using advanced software predictive tools showed that beetles are closely related with horseshoe crabs than common crabs (Class: Melacostraca). It was interesting to note that terrestrial Scorpion (Class: Arachnida) were distantly related to horseshoe crabs (Class: Merostomata). Phylogram and observed Genetic Distance (GD) data were also revealed that Limulus polyphemus was distantly related to all the other horseshoe crab species. Tachypleus gigas was closely related with Carcinoscorpius rotundicauda than with Tachypleus tridentatus. The observed mean Genetic Distance (GD) value was higher in 3rd codon position in all the selected group of organisms. Among the horseshoe crabs high GC content was observed in L. polyphemus (38.32%) and lowest was observed in T. tridentatus (32.35%). We conclude that COI sequencing (barcoding) could be used in identifying and delineating evolutionary relatedness with closely related species."

    Comprehensive dry lab methodology with advanced software predictive tools? What? That turns out to mean "neighbor joining with Kimura 2-parameter distances". Urk. But at least the abstract makes no claims about anything other than the ability to determine relationships among horseshoe crabs. Nothing about crabs or scorpions there. Sadly, that does come up in the full publication, which suggests that horseshoe crabs evolved from aquatic insects!

    Larry, this could never have been published in a reputable journal. Bad citation.

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    1. I wasn't defending the phylogeny. I was only using this paper to point out that horseshoe crabs have evolved as evidenced by molecular data. It was just the latest on in the PubMed list.

      I assume you don't dispute the fact that horseshoe crabs are evolving at the same rate as every other species?

      I've modified the post to make this point more clear.

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    2. No, I understood your point, as should be clear. But you had also mentioned the deep relationships in the tree rather credulously, and those are bogus. I wouldn't say that horseshoe crabs are evolving at the same rate as every other species, since there is quite a bit of variation in rate among species and among loci within species. And we can't tell much about the rate from the tree you give, since the lengths of the deeper branches, especially, are likely to bear little resemblance to the true amount of CO1 evolution along them (even the ones that really exist). But your point was they aren't living genetic fossils. That's still there.

      I merely wanted to point out that the publication in question was amazingly bad and that nobody should believe anything in it, with the possible exception of the relationships among horseshoe crab species.

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  11. "These anomalous forms [that are similar to known fossils] may be called living fossils; they have endured to the present day, from having inhabited a confined area, and from having been exposed to less varied, and therefore less severe, competition." (Darwin, Origin, 6th edition). Darwin suggests that reduced change was due to reduced competition. Later on the same page he states that evolution by natural selection only acts "when there are places in the natural polity of a district [= ecological niches] which can be better occupied by the modification of some of its existing inhabitants." Thus, until population genetics got going, there was no need for biologists to expect that evolution would necessarily occur. It was contingent upon ecological opportunity. Since genetic drift was discovered by population geneticists in the 1930s and, more especially, the revelations of molecular biology in the 1950s, both drift and non-morphological adaptive evolution have become increasingly understood. Living fossils were from the beginning compatible with materialistic views of evolution, but they are not by themselves evidence for evolution. However, the molecular phylogenies of "living fossils" are evidence.

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  12. I simply do not see anywhere in Fortey's statement where he says that the horseshoe crab has not evolved. He is pointing out that they are "basically" the same in general body plan to the earlier forms, not that they are identical. His point is that they are relatively conservative and that morphological evolution does not necessarily involved major changes. That's all he is saying. And it is important to note that this happens, because evolutionists have been accused of treating evolution as a quasi-religious worship of the idea of progress. That his words were misused by IDiots is no reason to attack him.

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  13. He's talking about stabilizing selection on morphological phenotypes.
    You, as always, are focused on strictly molecular traits.

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