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Sean Carroll has doubts on nanotech:
Living organisms … can, in a wide variety of circumstances, repair themselves. … Which brings up something that has always worried me about nanotechnology … tiny machines that have been heroically constructed … just seem so darn fragile. … surely one has to worry about the little buggers breaking down. … So what you really want is microscopic machinery that is robust enough to repair itself. Fortunately, this problem has already been solved at least once: it’s called “life.” … This is why my utterly underinformed opinion is that the biggest advances will come not from nanotechnology, but from synthetic biology. (more)
There are four ways to deal with system damage: 1) reliability, 2) redundancy, 3) repair, and 4) replacement. Some designs are less prone to damage; with redundant parts all must fail for a system to fail; sometimes damage can be undone; and the faster a system is replaced the less robust it needs to be. Both artificial and natural systems use all four approaches. Artificial systems often have especially reliable parts, and so rely less on repair. And since they can coordinate better with outside systems, when they do repair they rely more on outside assistance – they have less need for self-repair. So I don’t see artificial systems as failing especially at self-repair.
Nevertheless, Carroll’s basic concern has merit. It can be hard for new approaches to compete with complex tightly integrated approaches that have been adapted over a long time. We humans have succeeded in displacing natural systems with artificial systems in many situations, but in other cases we do better to inherit and adapt natural systems than to try to redesign from scratch. For example, if you hear a song you like, it usually makes more sense to just copy it, and perhaps adapt it to your preferred instruments or style, than to design a whole new song like it. I’ve argued that we are not up to the task of designing cities from scratch, and that the first human-level artificial intelligences will use better parts but mostly copy structure from biological brains.
So what determines when we can successfully redesign from scratch, and when we are better off copying and adapting existing systems? Redesign makes more sense when we have access to far better parts, and when system designs are relatively simple, making system architecture especially important, especially if we can design better architecture. In contrast, it makes more sense to inherit and adapt existing systems when a few key architectural choices matter less, compared to system “content” (i.e., all the rest). As with songs, cities, and minds. I don’t have a strong opinion about which case applies best for nanotech.
Adapt Or Start Over?
The problem is that essentially all systems that are tolerant to some faults generate different faults.
This is the major cause of the diseases of modern civilization, including degenerative diseases such as Alzheimer's.
When an organism enters the “fight or flight” state, (as when running from a bear), where to be caught is certain death, being “fault tolerant” in that case means turning off repair so as to divert resources to immediate consumption. A few extra molecules of ATP are wasted if used for healing if the bear catches you, but if healing is turned off, that ATP can be diverted to the legs and used for a few more steps and potential escape.
The brain (and all tissue compartments) exhibit what is called “ischemic preconditioning”, where several brief exposures to ischemia induce a state where the tissue compartment is much more resistant to prolonged ischemia than without the preconditioning. My interpretation of this universally observed behavior, is that brief periods of ischemia induce physiology to change state to a state where ATP consumption is lower, and so the loss of ATP producing substrates (blood and O2) is better tolerated. Resources are diverted from long term needs (maintaining DNA error free for example) to short term needs (staying alive for the next few minutes). During an ATP “crisis” (where there is not enough ATP to do everything that the organism would like to do), ATP consuming pathways that take longer than the duration of the crisis can safely be turned off and any ATP they would have used can be diverted to surviving the short term crisis.
Can the ischemic preconditioned state be maintained long term? Pretty obviously it cannot, otherwise organisms would have evolved to be in that state continuously (so more resources could be devoted to reproduction), and so would not exhibit ischemic preconditioning.
There has to be a hierarchy of physiology which prioritizes survival over repair of organs, and repair of organs over repair of DNA. Once the DNA starts to pick up errors, it is a one-way street to degeneration and death.
The problem is that in evolved organisms, these different pathways are all self-regulating and they are regulated to the priority hierarchy that evolved, which only prioritized survival leading to reproduction.
It should be possible (in principle), to design an organism from scratch, but the stress responses that program the ATP hierarchies are from such deep evolutionary time that a non-aging organism would really need to be designed from scratch. Even bacteria prioritize survival over maintaining DNA fidelity. An organism that prioritized long term survival over short term voluntary activity would have to be pretty clunky. If you spend 10x more on maintenance and repair, you can probably get a multiple of lifespan. But that increased maintenance has to be done for the whole lifespan, not just the increment. That is mostly what basal metabolism is now. You can't increase that by 10x, you have to reduce the part that is not devoted to repair.
The firefly is capable of producing a "cold light" with a wavelength from 0.00051 to 0.00067 millimeters, pale greenish-yellowish with a light efficiency of 96%. The ordinary incandescent light has an efficiency of roughly 10%, most of the energy being wasted as heat.
The firefly goes all he way from chemical energy to light at 96% efficiency if we could approach that it would be amazing. I think all animal must be able to go from chemical energy to electricity at better than 96% efficiency wow.