We have a short list of systems we like to call “optimizers” — the market, natural selection, human design, superintelligence. I think we ought to hold the immune system in comparable regard; I’m essentially ignorant of immunobiology beyond a few YouTube videos (perhaps a really fantastic LW sequence exists of which I am unaware), but here’s why I am thinking this.
The immune system is the archetypal anti-optimizer: it defends a big multicellular organism from rapidly evolving microbiota. The key asymmetry:
Specified once by the genome. It cannot rewrite its own source code between generations. Its adversaries evolve orders of magnitude faster.
Resource asymmetry as counterbalance. Whole organs are devoted to the adaptive immune response. A microbe is one cell; the immune system is a civilization.
This extends to cancer. The immune system typically out-adapts malignant cells despite selection acting far more rapidly on them. Immunosurveillance fails not because it is weak but because cancers occasionally evolve to exploit its specific tolerance mechanisms.
In short: the immune system embodies enough amortized optimization power to defend against online adversarial attacks by natural selection, because these attacks are constrained by the comparative simplicity of the attackers. One optimizer constrains another, faster and more adaptive optimizer, by having more resources.
What makes this especially interesting is that the immune system has no discernible volition. It is complex — probably far more so than I appreciate — but intuitively much more like a thermostat than a scheming eldritch god. It optimizes powerfully, within bounds that feel legible and non-agential.
I will not be so crass as to say “big if true for alignment”, but you are permitted to infer this if it please you. I just think it’s neat. Consider the mere phrase “semiotic immune system” (from, if I recall correctly, Charles Stross’s Accelerando) — suggests a lot at once, eh?
One nitpick is that the a part of the immune system (your population of B-cells) can rewrite its source code between generations, and surprisingly rapidly! In fact, because their goal is to produce antibodies which grab on to pathogens, B-cells will actually mutate the genes encoding for these antibodies at an extraordinary rate. And, they’ll reproduce more the more their antibodies are shown to work (that is, to bind to a piece of a pathogen!) This allows your body to run evolution far faster than a lot of microbes, which have selfish genes that “want” to be passed on without mutation.
Now, your main thesis still remains. The adaptive immune system, which includes all B-cells, is only found in vertebrates. The majority of the animal kingdom does have an immune system which is specified once, and they get by just fine. However, it’s also worth noting that the largest and most complex animals are ~all vertebrates, and this might have something to do with the immune system, among other things.
re point 2 - you say “A microbe is one cell”, but the immune system has to battle against a constant onslaught or widely different invaders. I’m not sure the asymmetry is accurate. Researchers found that frail people over 60 had a low Colony Forming Unit per Gram (CFU/g) score of under 10⁴ CFU/g. At the very least people will eat one of two types of food-microial content: lactic acid bacteria, yeast molds, but there are others. This says nothing about viruses or non-dietary contact. Sauerkraut alone contains: Leuconostoc mesenteroides, Lactobacillus plantarum, Pediococcus pentosaceus, Lactobacillus brevis, Leuconostoc citreum, Leuconostoc argentinum, Lactobacillus paraplantarum, Lactobacillus coryniformis, and Weissella spp. Kimchi contains the bacteria Leuconostoc spp., Weissella spp., and Lactobacillus spp according to Wikipedia.
Yup I definitely agree there’s no special role for unicellular attackers—I was eliding the complexity for brevity. I think the asymmetry still broadly holds meaningfully—e.g. multicellular parasites are very complex attackers but have much longer generation-times (I assume?), so they too trade off online vs offline optimization bits. Nonetheless the host organism still has more complexity to draw on for most things with which the immune system is concerned.
Interesting to think about the pareto frontier of offline vs online optimization. The multicellular parasites and unicellular microbes would be paradigm examples. But the microbiome gives lie to this idea—it is complex and organized but highly adaptive still because selection can act on the lower level. Perhaps being ~commensal/mutual instead of adversarial is related? I don’t know.
The Immune System as Anti-Optimizer
We have a short list of systems we like to call “optimizers” — the market, natural selection, human design, superintelligence. I think we ought to hold the immune system in comparable regard; I’m essentially ignorant of immunobiology beyond a few YouTube videos (perhaps a really fantastic LW sequence exists of which I am unaware), but here’s why I am thinking this.
The immune system is the archetypal anti-optimizer: it defends a big multicellular organism from rapidly evolving microbiota. The key asymmetry:
Specified once by the genome. It cannot rewrite its own source code between generations. Its adversaries evolve orders of magnitude faster.
Resource asymmetry as counterbalance. Whole organs are devoted to the adaptive immune response. A microbe is one cell; the immune system is a civilization.
This extends to cancer. The immune system typically out-adapts malignant cells despite selection acting far more rapidly on them. Immunosurveillance fails not because it is weak but because cancers occasionally evolve to exploit its specific tolerance mechanisms.
In short: the immune system embodies enough amortized optimization power to defend against online adversarial attacks by natural selection, because these attacks are constrained by the comparative simplicity of the attackers. One optimizer constrains another, faster and more adaptive optimizer, by having more resources.
What makes this especially interesting is that the immune system has no discernible volition. It is complex — probably far more so than I appreciate — but intuitively much more like a thermostat than a scheming eldritch god. It optimizes powerfully, within bounds that feel legible and non-agential.
I will not be so crass as to say “big if true for alignment”, but you are permitted to infer this if it please you. I just think it’s neat. Consider the mere phrase “semiotic immune system” (from, if I recall correctly, Charles Stross’s Accelerando) — suggests a lot at once, eh?
I asked Claude to prepare the following tutorial—which I have not yet read (longa est vita, si uti bene scias...) - developing this theme: https://claude.ai/share/67bb8de3-b73c-4a21-916b-70affba0da43
*Written with slight corrections for conciseness from Opus4.6. Ironically, the em-dashes are mine.
One nitpick is that the a part of the immune system (your population of B-cells) can rewrite its source code between generations, and surprisingly rapidly! In fact, because their goal is to produce antibodies which grab on to pathogens, B-cells will actually mutate the genes encoding for these antibodies at an extraordinary rate. And, they’ll reproduce more the more their antibodies are shown to work (that is, to bind to a piece of a pathogen!) This allows your body to run evolution far faster than a lot of microbes, which have selfish genes that “want” to be passed on without mutation.
Now, your main thesis still remains. The adaptive immune system, which includes all B-cells, is only found in vertebrates. The majority of the animal kingdom does have an immune system which is specified once, and they get by just fine. However, it’s also worth noting that the largest and most complex animals are ~all vertebrates, and this might have something to do with the immune system, among other things.
re point 2 - you say “A microbe is one cell”, but the immune system has to battle against a constant onslaught or widely different invaders. I’m not sure the asymmetry is accurate. Researchers found that frail people over 60 had a low Colony Forming Unit per Gram (CFU/g) score of under 10⁴ CFU/g. At the very least people will eat one of two types of food-microial content: lactic acid bacteria, yeast molds, but there are others. This says nothing about viruses or non-dietary contact. Sauerkraut alone contains: Leuconostoc mesenteroides, Lactobacillus plantarum, Pediococcus pentosaceus, Lactobacillus brevis, Leuconostoc citreum, Leuconostoc argentinum, Lactobacillus paraplantarum, Lactobacillus coryniformis, and Weissella spp. Kimchi contains the bacteria Leuconostoc spp., Weissella spp., and Lactobacillus spp according to Wikipedia.
Yup I definitely agree there’s no special role for unicellular attackers—I was eliding the complexity for brevity. I think the asymmetry still broadly holds meaningfully—e.g. multicellular parasites are very complex attackers but have much longer generation-times (I assume?), so they too trade off online vs offline optimization bits. Nonetheless the host organism still has more complexity to draw on for most things with which the immune system is concerned.
Interesting to think about the pareto frontier of offline vs online optimization. The multicellular parasites and unicellular microbes would be paradigm examples. But the microbiome gives lie to this idea—it is complex and organized but highly adaptive still because selection can act on the lower level. Perhaps being ~commensal/mutual instead of adversarial is related? I don’t know.
Note: Skimming, Claude hallucinates what Alon’s ‘periodic table of diseases’ is. He has a pretty good youtube video on it you can watch instead. https://www.youtube.com/watch?v=ZMz_C778WMY&pp=ygUeYWxvbiBwZXJpb2RpYyB0YWJsZSBvZiBkaXNlYXNl
The linked Claude conversation doesn’t share the markdown file unfortunately. Apologies. Here is a gdrive link https://drive.google.com/file/d/1wpPGI7poP04ZMDoPU_lEh8D1CI8kOtic/view?usp=sharing I read it and it was a good introduction but it did a mediocre job of reframing things ‘as an optimizer’ or even ‘as a control system’.