The Evolution (through natural selection) of the Immune System

[mooeypoo]

Hey guys,

 

Anyone following the Dover case could see Dr Behe's rediculous approach to the dozens of books explaining the evolution of the immune system through natural selection.

 

I find the subject of evolution in general fascinating, but most of the resources I found online about the evolution of the Immune system were *waaaaay* beyond my level.

 

I am not sure if I was just unable to find any good 'lay men' resources or if it's just a dificult subject, but I was wondering if anyone could perhaps give me a brief layman explanation on how the immune system evolved.. where does it come from?

 

Or.. well.. resources would be fine too.

 

Thanks!

 

~moo

[iNow]

I am not sure if I was just unable to find any good 'lay men' resources or if it's just a dificult subject, but I was wondering if anyone could perhaps give me a brief layman explanation on how the immune system evolved.. where does it come from?

 

Those who had no defense against attack on the body tended to die before reproducing

 

Those who had a physiological response which mitigated attack on the body tended to reproduce.

 

Those who had a physiological response which mitigated attack on the body tended to reproduce more than those which did not.

 

Badda bing. Evolution of the immune system.

 

 

 

The organisms that had better defenses had better reproductive success than those which did not. Hence, the trait was selected.

 

 

Too elementary?

[CharonY]

A very interesting if complex topic. One problem with a short answer is the overwhelming complexity of mammalian immune response, which is very multi-faceted. Regarding specifically the adaptive immune system, are you familiar with the transposon hypothesis?

[iNow]

Regarding specifically the adaptive immune system, are you familiar with the transposon hypothesis?

 

What's that?

[Mr Skeptic]

How does the whole immunization thing work? Does the immune system actively learn how to make proteins with specific properties (ie, antibodies)? Seems like that would be a very useful research tool if we could "tame" it.

[mooeypoo]

Those who had no defense against attack on the body tended to die before reproducing

 

Those who had a physiological response which mitigated attack on the body tended to reproduce.

 

Those who had a physiological response which mitigated attack on the body tended to reproduce more than those which did not.

 

Badda bing. Evolution of the immune system.

 

 

 

The organisms that had better defenses had better reproductive success than those which did not. Hence, the trait was selected.

 

 

Too elementary?

 

Hehe that's a BIT too elementary, yeah. I understand the logic behind it (btw, I can't imagine why creationists used this as an 'irreducible complexity' when it's so intuitive to explain...) but the actual level -- we're talking, technically, (or.. well, almost.. i think..) about a symbiotic relationship between us and a set of rather complex organisms that protect us. Furthermore, I think I read somewhere that it's not just the immune system in the blood, but also our symbiosis with "good" bacteria that protects us.

 

So .. yeah.. something a BIT more elaborate, please

 

or.. resources to one. whichever

 

thanks!

 

~moo

[CharonY]

we're talking, technically, (or.. well, almost.. i think..) about a symbiotic relationship between us and a set of rather complex organisms that protect us

 

I am not sure what you mean by that, to be honest. If one talks about immune response one usually refers to one of the many defense system an organism employs to combat other invading organisms. As such it cannot be viewed as symbiosis (which requires at least two different species).

 

Regarding the transposon hypothesis: it refers to the adaptive immune response which specifically recognizes antigens and thus triggers specific immune reactions. The fascinating thing about it is that it can recognize an almost unlimited amount of antigens, despite the fact that there are only a limited number of genes, coding for antibodies. The trick is that the genes are shuffled to modify the antigen binding sites and thus generate the observable variance.

The genes responsible for this shuffling are the so-called RAG (recombination activating genes) genes. The transposon hypothesis states that (based on sequence similarities) that the Rags were once transposase genes. A transposase is an enzyme, responsible for the transposition of certain mobile genetic elements, the transposases.

So the theory states that initially early vertebrates possessed an innate immune system with non-recombining receptors for antigens. Then a transposon moved into the respective gene(s) and then was cut out again. However the second excision was imperfect (e.g. part of the receptor was also cut out), resulting in a modification of the receptor in question. This mutated receptor was then able to better recognize new or modified antigens and natural selection would favour the spread of this variant.

Eventually this mechanism would evolve into the adaptive immune system known in jawed vertebrates.

Other aspects of the immune response are far older, btw.

[jorge1907]

Capabilities (immunity) do not evolve - beings do.

[iNow]

Capabilities (immunity) do not evolve - beings do.

 

This is a rhetorical interesting comment, but I fear it is far from accurate.

[CharonY]

This is a rhetorical interesting comment, but I fear it is far from accurate.

 

Indeed, especially in the light of modern genomic analyses. It is now (actually for a while) clear that for instance:

- protein coding sequences are often phylogenetically older than the species bearing them (in other words, phylogeny of coding sequences does not necessarily correlate with that of the organism)

- genomic DNA might arise from proliferation of DNA that have evolved to proliferate within genomes instead of benefiting the organism bearing them

 

It is also clear that some of the implicit and explicit assumptions of the modern synthesis, including the assumption that the durable unit of evolution are in fact species, have been refuted.

[vampares]

Forget the immune system, try his Irreducible Complexity.

 

It's like this:

I have a Lincoln Towncar, and I show this Towncar to a native.

 

If the Towncar doesn't start, it sucks.

 

If the Towncar's rearview mirror falls off when the native is putting on warpaint, it sucks.

 

If the window won't go up because a bunch of little native babies took the stereo, it sucks.

 

If it drips oil on the natives driveway, it sucks.

 

But when your riding shotgun in a full boat while running over the neighboring tribes mailbox, then it kicks ass. And that feeling right there, when the one side of the car is up on the sidewalk, that is Irreducibly Complex.

[Dak]

I find the subject of evolution in general fascinating, but most of the resources I found online about the evolution of the Immune system were *waaaaay* beyond my level.

 

I am not sure if I was just unable to find any good 'lay men' resources or if it's just a dificult subject, but I was wondering if anyone could perhaps give me a brief layman explanation on how the immune system evolved.. where does it come from?

 

the immune system is quite complicated. just getting a veigue overview was quite a shoker in my BSc...

 

having said that, i think i remember that lectins are present in simpler immune-systems, and act kinda like 'static' antibodies, so it's thought that at least that branch of our immune system is a hang-on from older, simpler immune systems. that might be one place to start?

 

lectins, btw, are sugars that bind to certain common components of bacteria, and can cross-link them to form 'clumps' of bacteria. being clumped inhibits bacterias actions (crossing intestinal walls, infecting cells, etc). also, iirc macrophages have lectin-receptors, and when enough of them are triggered the macrophage will start eating (hence: in higher chordates, once something has been clumped by lectins it gets eaten by macrophages, thus getting rid of it and bringing it to the attention of the adaptive immune system).