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  Topic: immune system evolution, collecting references to recent articles< Next Oldest | Next Newest >  

Posts: 319
Joined: May 2002

(Permalink) Posted: July 25 2003,08:59   



Not moving the goalposts quite yet. From DBB:

In this chapter I have looked at three features of the immune system - clonal selection, antibody diversity, and the complement system - and demonstrated that each individually poses massive challenges to a putative step-by-step evolution. [Niic, for the sake of argument, I'll grant you this one]. But showing that the parts can't be built step by step only tells part of the story, because the parts interact with each animal that has a clonal selection system won't get much benefit out of it if there is no way to generate antibody diversity. A large repertoire of antibodies won't do much good if there is no system to kill invaders. A system to kill invaders won't do much good if there's no way to identify them. At each step we are stopped not only by local system problems, but also by requirements of the integrated system.
Um, jon_e, haven't you gathered (from this thread and from Inlay's FAQ), that Behe's three systems are in fact separable, because they are built on each other in a phylogenetic sequence?  To wit:

(1) Invertebrates (echinoderms, tunicates, etc.) and lower vertebrates (hagfish and lampreys) have just the complement system

(2) Cartilagenous fish have the complement system + rearranging antibody diversity

(3) Tetrapods (well, most of them) have the complement system + rearranging antibody diversity + clonal selection (IIRC)

So in fact you don't need all three systems together.  Rather, the systems were added one-by-one, each building on the previous.  Once again, Behe is contradicted by very basic immunological facts.

Moving on:


Now, let me move from Behe to one of your earlier sources, the recent (but out-of-date) collection of articles by a number of experts in the field, Origin and Evolution of the Vertebrate Immune System
(Current Topics in Microbiology and Immunology, 248). "New Approaches Towards an Understanding of Deuterostome Immunity" J. P. Rast et al


Both of these attributes, the tendency towards mechanistic novelty and a high rate of sequence evolution, may emerge from the dynamic nature of host-pathogen interactions and thus be a universal characteristic of immune systems.

Universal, Niic, universal.
Now, I'm not sure if Rast et al are talking about the same thing as Behe exactly, but it would seem to me that the points they are making are very similar. In order for an immune system of any type to work properly, several features need to be present all at once. Why else would the authors be proposing universality for "the tendency towards mechanistic novelty and a high rate of sequence evolution?"
Unfortunately, jon_e, you're reading something into the quote that just ain't there.  They're not talking about parts of a system reacting within an organism, they're talking about the diversity of one basic component, the receptor, and how natural selection favors receptor diversity in evolution.

What they are talking about is the fact that it is beneficial for the organism to have diverse antigen receptors, because then more kinds of potential invaders can be bound and destroyed.  Therefore, there is selection for duplication and diversification of receptor genes.  E.g., humans have many slightly different homologs of both non-rearranging and rearranging receptor genes.  The pattern of diversity is also found in organisms that only have non-rearranging receptors -- they apparently get all the diversity they need by encoding diversity in the germline.  The somatic rearrangement that occurs in vertebrates is simply an enhancement to this diversity.

It is, in fact, a classic case of positive selection:


Immunol Rev. 2002 Dec;190:161-8.

Natural selection and the diversification of vertebrate immune effectors.

Hughes AL.

The molecules of the vertebrate immune system provide some of the best documented examples of natural selection acting at the molecular level. The major histocompatibility complex (MHC) molecules are a family of highly polymorphic loci whose products present peptides to T cells. Four distinct lines of evidence support the hypothesis that the natural selection acts to maintain MHC polymorphism: (1) evidence from the unusual allelic frequency distribution seen at MHC loci; (2) evidence from the pattern of nucleotide substitution at MHC loci, which shows an enhanced rate of nonsynonymous (amino acid-altering) substitution in the codons encoding the peptide-binding region of the molecules; (3) the existence of long-lasting polymorphisms at certain MHC loci; and (4) the fact that introns at MHC loci are homogenized by recombination and subsequent genetic drift. Certain other immune system gene families provide evidence that natural selection has acted to create diversity among family members. Examples include molecules of the specific immune system (such as immunoglobulin V region genes) and molecules of the innate immune system (such as defensins).
Another reason for this diversity is that the invading pathogens are continually evolving *away* from being recognized by current receptors, so there is continual selection on the organism for new receptor genes to evolve to "track" the diseases.

So now we can see that your excited conclusion:


It's interesting to me that those few words seem to sum up a major hurdle for the standard Darwinistic explanation of things - if I understand them correctly, they are suggesting that every creature that has, or has ever had, an immune system, has the ability to respond very quickly to the presence of enemy organisms, creating new features or substances on-the-fly so to speak, and to generate a high rate of sequence evolution (are they refering to a high rate of somatic mutations?) in response to the threat.
...was based on a misconception.  The "response" "creating new features or substances" is an *evolutionary* response that occurs in populations, not individual organisms.  The exception is rearranging receptors+clonal selection, which *does* allow "within organism" evolution of a sort, but which is not found invertebrates etc.


As I keep saying over and over, "the immune system" as a whole is big and ill-defined.

Now, do you mean by this that features of the immune system are difficult to explain or describe?

[snip quote]

Or what? Your comment seems to contradict your basic claim that Dembski and Behe are all wet regarding current research and literature. What is it, exactly, that you mean by your comment?

Jon_e, look.  What I was trying to do was distinguish between one of Behe's specific IC system, receptor rearrangement, which is reasonably well-defined with three basic molecular components, vs. the whole immune system, which is not similarly well-defined.  You were continually confusing the rearranging receptors with the immune system as a whole, and I was trying to get you clear that these are not equivalent things.

I was also pointing out that in general "the immune system" doesn't fit the IC box very well at all.  Most of the vertebrate system is lacking in other animals, many of the "parts" have immunity and non-immunity-related functions, etc. You still haven't told me whether or not you think that skin is part of the immune system.  Various cells are definitely a part of the immune system, but cells are a long ways from Behe's "molecular machine" paradigm for defining a system.  We could add mucous membranes and a human prediliction for cleanliness if we wanted to.  And then we have organismal variations.  A sponge with just a few primitive non-rearranging receptors has an immune system of a sort.  This is the problem with defining "the" immune system.

But the definition of "immune system" is really a side-show, you're not going to find the salvation of Behe and Dembski there.


Or do you mean, It's difficult to cram the immune system into the restrictive, overly reductionistic and simplistic non-explanations of classical Darwinian theory?
You want a "non-explanation", here's one: "Poof".  That's all the IDists have.  We evolutionists, on the other hand, have oodles of literature.  My only beef at the moment is that Behe and Dembski are misleading you all by saying that this literature doesn't exist.

Based on what you've learned in this thread, jon_e, what do you think of Behe's statement from Darwin's Black Box, p. 138?

"We can look high or we can look low, in books or in journals, but the result is the same. The scientific literature has no answers to the question of the origin of the immune system."
Is this an accurate or misleading statement, jon_e?

  23 replies since Dec. 17 2002,18:45 < Next Oldest | Next Newest >  


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