Zimmer on Antibodies

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Carl Zimmer has written another good post on his blog about the evolution of the immune system: The Whale and the Antibody.

You can find this same remarkable system in humans, albatrosses, rattlesnakes, bullfrogs, and all other land vertebrates. You can also find it in most fish, from salmon to hammerhead sharks to sea horses. There are some variations from species to species, but they’ve all got B cells, T cells, antibodies, thymuses, and the other essential components. But you won’t find it in beetles, earthworms, dragonflies, or any other invertebrate on land. Nor will you find it in starfish, squid, lobsters, or lampreys in the water. All these other animals rely instead on rudimentary immune systems that cannot learn.

For those who reject evolution, this sort of pattern tells them nothing. Like everything else in nature, they can only wave their hands and declare it the inscrutable work of a designer (lower case d or upper case D as they are so inclined on a given day). But immunologists and other scientists who actually want to learn something about the immune system find this view useless. Instead, they look at how animals with an antibody-based immune system are related to one another. And what they find is both straightforward and astonishing. All of the living animals with an antibody-based immune system descend from a common ancestor, and none of the descendants of that common ancestor lack it. That means that the antibody-based immune system evolved once, about 470 million years ago.

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Happy New Year, ID movement! (Evolutionary Immunology vs. ID, and predictions for 2005) Read More

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The Zimmer post is another example of why Carl Zimmer is quickly becoming everyone’s (well, almost everyone’s) favorite science writer. Great job Carl!

Gosh I would love to see Science or Nature do a special series on evolutionary immunology. With that GOD article in the lamprey that appeared a few months ago, it seems like a topic ripe for the picking.

Carl Zimmer Wrote:

For those who reject evolution, this sort of pattern tells them nothing. Like everything else in nature, they can only wave their hands and declare it the inscrutable work of a designer (lower case d or upper case D as they are so inclined on a given day)

And whatever the day, one can always count on them to use weasel words like “common design.” It’s as if they all know - and some surely do - that the specific conceivable alternatives, be it independent abiogenesis, saltation, or front-loading, are still the extraordinary claims without the requisite extraordinary evidence.

Wow, that article (“The descent of the antibody-based immune system by gradual evolution”) really sticks it to the ID movement’s “irreducibly complexity” movement.

Of course, even though the article does stick it to the ID movement, it does so unintentionally. The text actually completely ignores the ID movement (justifiably, as the ID movement itself completely ignores the massive amount of research on evolutionary immunology). It’s quite possible that the authors have never even heard of ID. Instead, Klein and Nikolaidis are going after the “big bang” model of the evolution of the immune system, which credited two whole-genome duplications with the rapid transition between an agnathan-grade system and a gnathostome (jawed-vertebrate)-grade:

Conclusion and Prospects

According to a currently popular view, the “big bang” hypothesis (10, 11), the AIS arose suddenly, within a relatively short time interval, in association with the postulated two rounds of genome-wide duplications (64). That a number of genes have duplicated during the transition period from agnathans to gnathostomes is undeniable. However, how extensive this genomic expansion was remains controversial (65). If the duplication rate did indeed increase in the agnathan–gnathostome transition interval, it might have contributed to the appearance of AIS by providing the necessary “raw material” for the final integration of the emerging AIS into the other immune systems. The evolution of the AIS itself, however, must have begun long before the divergence of agnathans and gnathostomes from their common ancestor. The evolution consisted initially of changes unrelated to immune response that were selected to serve other functions. The different functions may have been unrelated to one another, but ultimately, a combination of these functions arose by chance, which presented the potential for the development, in a not too large number of small steps, of a qualitatively new system. The actualization of the potential required integration of the different functions into one whole. The necessary steps for this integration were undertaken in the gnathostome lineage, whereas the agnathans evolved in a different direction (66). Once the critical steps were accomplished in the gnathostome lineage, the integration created the illusion of a sudden, explosive change, a big bang. However, in reality, the entire process was gradual, consisting of accumulation of small changes over an extended period (Fig. 2).

I actually find this kind of debate within evolutionary science a bit tenditious, because in actuality the descriptors “gradual” and “rapid” are not really opposed when the terms are used in their evolutionary senses. “Gradual” just means step-by-step (and viable molecular “steps” can be “larger” than steps at the morphological level – e.g., domain swapping between proteins). “Rapid” means “geologically rapid,” which, based on usage, can apparently be anything less than 100 million years (in the case of the “big bang” hypothesis for the immune system, I believe the interval between the agnathan-gnathostome divergence and the sharks-nonsharks divergence is supposed to be about 50 million years). You can fit an immense amount of gradual change into a “rapid” 50,000,000 years.

Let me get this straight.

We don’t know whether 100 million year old dinosaurs were warm or cold blooded but we’re claiming to know what kind of immune system cells were floating around the bloodstreams of creatures that preceded them by up to 400 million years?

Gimme a break. Until you have 100 million or 400 million year old blood to analyze you’re just guessing about it and asking people to have faith in your guesses.

I’m not buying it. I’m an agnostic and we don’t take things on faith from creationists OR evolutionists.

How many Google hits will it take to convince you, DaveScot?

DaveScot: Suppose there’s a tribe in Africa that claims, based on old legends, that they descended from Jews, despite the fact that they look entirely African, and not at all Jewish. If we could analyze the genome of the living members of the tribe, and found similarities to the genomes of living Jewish people (similarities that no other African tribe possessed), would you consider that evidence of their claim, even though we don’t have the DNA of the original population?

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This page contains a single entry by Reed A. Cartwright published on December 31, 2004 2:14 PM.

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