Does your squeamishness decrease if, instead of cloning, we were able to use tissue engineering in vitro to directly grow all the relevant adult organs and the vasculature and connective tissues between them? Subjectively, mine does, even if this path seems more difficult to me.
Also, buying ourselves an extra century to solve the problem of the aging brain seems like a big deal, too.
I would have zero squeamishness in such a situation, it just seems like a far more difficult problem.
You completely ignored the biology of how much life extension you would actually get even if you solve all the technical challenges. Many old people do get Alzheimer's and other diseases of old age.
Relearning how to move a new body is a highly nontrivial task. If you have a gut nervous system that never interacted with an awake brain and you suddenly plug an adult brain to it, you should not assume that the process happens without any side effects.
I do discuss that briefly in the first section, and the footnote.
In short this question heavily revolves around how much a young body reduces risk of brain disease in an old brain. We have some reasons to think a reduction is likely, but absent empirical studies (very difficult without first solving the technical challenges), almost impossible to quantify by how much.
It depends on the how much the procedure of being wired to a body that's not the original body that the brain has learned to interact with and other surgery side effects as well.
You seem to just assume that those issues can all rounded down to zero, which isn't a sensible thing to do.
Great partial solution, but I don't know how practical it would be to get similar benefits to cloning the whole body.
Doesn't work because aging affects the brain as well and many deadly diseases originate in brain: insults, Alzheimer and brain cancers. Add risks of the transfer itself and the uncertainty when it should be done: too early for healthy aged person and and too late for one with cancer of any type (risks of metastases). All together it gives less than 10 years increase of of medium life expectancy.
Just checking: did you read this paragraph and disagree, or you didn't notice it?
The other is to transfer your brain from a decrepit dying body to a healthy young one, whenever your poor health starts to bother you. This won't cure brain disease, but will at least mean that even if you do get dementia, your bones won't be aching all the time. I also suspect a young body would drastically reduce e.g. alzheimers development by e.g reducing inflammation, improving oxygen and nutrient support, clearing out toxins etc.
So a full brain transfer might let us live to 150 in mostly good health, as opposed to our current situation of 80 years, health getting steadily worse throughout.
In response to your comment:
insults, Alzheimer and brain cancers
As discussed,having a young body likely significantly reduces the incidence and severity of Alzheimers, and because brain cancers are often caused by metastatic body cancers, which are far likelier in older bodies, brain cancer as well.
Add risks of the transfer itself and the uncertainty when it should be done: too early for healthy aged person and and too late for one with cancer of any type (risks of metastases). All together it gives less than 10 years increase of of medium life expectancy.
Assume we can get risk of serious injury down to 1% - this seems doable for what will become the most common surgery on earth. Then most people switch to a 20 year old clone whenever their body reaches 50. This avoids the body ever getting too old, reducing the chances of any diseases ever developing in the first place.
I've created the following sheet to play around with the data: https://docs.google.com/spreadsheets/d/120SUIMLKFeUEzfG8NydSXf9_rGf7ROHcehUKDmUJwkw/edit?usp=sharing
It uses the Gompertz law to estimate the death rate at a given age.
It's got 4 variables you can play around with.
According to this model, we would see life expectancy of around 120 if we switched at age 50. We get best life expectency by switching at age 70, but that's an artifact of the simplified model, where transferring at a higher age doesn't increase risk past that point.
The variable that causes the greatest impact on life expectancy is how much transferring to a younger body reduces risk.
Gompertz law is really brutal. Let's assume that brain diseases causes 25 per cent of all death. At age 70 doubling of mortality is 7 years, so brain transfer reduces two doublings and gives +14 yeas to life expectancy.
However, around 105 years old doubling time is 1 year, so brain transfer will give only 2 years of life expectancy. Even if we reduce brain disease share in aging-related deaths to 1 per cent, the brain-transfer will give only around +7-8 years for centenaries, so 110 years is absolute limit for such technology. We have to address Gompertz law instead.
I think there will be some reduction, but bit will not change the outcome significantly.
1 First, there will be opposite process - old brain will affect young body by different hormones and different behavioral habbits (like no running). Also, old brain may have some dormant cancer cells from previous body which will propagate through young body.
2 Beneficial impact of young body will not affect all types of brain aging. May be 50 per cent slower aging which gives only one doubling or 7 years, but they will be mostly compensated by damage described in points 1 and 3.
3 The transfer procedure, if not required nanotechnology, will include a period of some brain ishemia or cooling, which will damage brain to some extent. And if we have advance nanotech, we don't need new biological body at all - we can grow new one through old one.
BTW, we are starting soon an analog of LessWrong about life extension, may be you will be interested to share your post there: https://antimortality.org/.
Problem 1. Long Iteration Cycles in Cloning
The first real problem with transplantation onto a non-conscious clone is that each iteration of growing such a clone takes many years. A billion people could die while we complete a single iteration. Moreover, the proposed threshold of 11 years is debatable — the true minimum developmental age may be closer to 18 years.
Problem 2. The Immunity Problem in Allotransplantation
Allotransplantation solves the problem of the absence of a clone, but introduces the problem of immune rejection. This may potentially be addressed through bone marrow hybridization.
Problem 3. Poor Scalability of Allotransplantation
Allotransplantation does not scale well.
Problem 4. The Complexity of Brain Transplantation
Transplanting the brain itself is significantly more difficult than transplanting the head. The brain is extremely soft — almost like panna cotta. In addition, there is the question of the brainstem: there is no reason to assume it is not critically important. Rehabilitation after a brain transplant would also require a far greater degree of neural relearning and adaptation.
Solution 1
Head transplantation may be preferable because it preserves a larger portion of the spinal cord and simplifies rehabilitation. There are already studies on spinal cord fusion, and the research groups involved continue advancing this work. However, the immunity problem would still remain.
Solution 2
There are two ways to improve scalability:
Remaining Problem
The remaining issue is the cerebral vasculature and the health of the blood-brain barrier (BBB). The encouraging aspect is that aging becomes localized to essentially one organ, which is far easier to address than systemic aging. The downside is that cerebral blood vessels are not adapted to a new heart, and altered pulsation dynamics could accelerate vascular damage.
Brain transfers could get off the ground if they would be positioned as an almost full-proof (except for brain cancer) cancer cure. In a future in which almost everything else could be "cured" but cancer becomes the most common cause of death (a scenario which isn't at all unlikely), a lot of pressure could build for using brain transfers. Brain cancer would still be a problem, but it would probably remain as rare as it is today. Metastasis of cancer to the brain would probably become just as rare due to improvements in early cancer diagnosis.
The continued degeneration of the brain might be at least partially solved by gradual replacement of the old brain itself. A big problem with this replacement strategy is that episodic memory would also be gradually destroyed by replacement cycles which would be designed to eventually replace the entire brain. Potential solutions range from constantly replaying all your memories in order to try to strengthen and preserve them in parts of the brain that won't be replaced during a single replacement cycle or scanning and then 3D printing sections of brain tissue that would act as replacement tissue. If these solutions won't work, the choice will be between certain death and gradual episodic memory loss. This situation won't be ideal (and might somewhat decrease the enthusiasm for brain transfers), but I suspect that a lot of (or most?) people will choose gradual memory loss.
Please read Jack Scalzi's "Old Man's War" series for a hilarious take on cloning, mind transfer, war, and SETI.
I don't actually think the program described below is a good idea. Take it more as a plot setting for a hard science fiction world if you want.
I want to live forever. Failing that I want to live for longer than 80 years, and in good health till just before I die.
Lots of people want the same and, are trying to work out how to make our body stay healthy longer. This is difficult, because all of our various body parts start failing around the same time for different reasons. I hope they succeed, but I wouldn't want to put all my eggs in one basket.
So are there other options which avoid this issue?
One is uploading. From what little I've heard, I'm not hopeful they'll get there in time.
The other is to transfer your brain from a decrepit dying body to a healthy young one, whenever your poor health starts to bother you. This won't cure brain disease, but will at least mean that even if you do get dementia, your bones won't be aching all the time. I also suspect a young body would drastically reduce e.g. alzheimers development by e.g reducing inflammation, improving oxygen and nutrient support, clearing out toxins etc.
So a full brain transfer might let us live to 150 in mostly good health[1], as opposed to our current situation of 80 years, health getting steadily worse throughout.
Ok.
What would the process of a brain transfer look like?
First we'd need to clone unconscious versions of ourselves, and keep them alive and healthy till at least age 11 when the skull will be large enough for our adult brain, but ideally till 18 to avoid... issues.
Then we'd have to remove the brain from our current body, and attach it to the new body, keeping it alive the whole time.
What new technologies would we have to develop to solve this?
Human Cloning
While we haven't cloned humans yet, cloning is a well understood technology. There are specific barriers that make cloning primates more difficult than say sheep, but I would be surprised if these problems wouldn't be solved with a concerted effort. At this stage its an engineering problem more than a wide open hypothetical problem.
Keeping an unconscious human alive and healthy
We know how to make someone brain-dead. We also know how to make someone unconscious, both permanently and temporarily. There are people who have woken up after decades in a coma, and medically induced comas can last months if necessary.
However there are particular challenges here:
I have no idea if this is merely an engineering problem, requires new insights, or is fundamentally impossible. If anyone knows more, I'd love to hear.
Transferring the brain
We know a lot about organ transfers. We know how to keep an animal brain alive for hours even once removed from the head. The tricky bit is reattaching it afterwards.
We know how to reattach blood vessels and tissues. The difficult bit is nerves:
The brain has one spinal chord and 12 pairs of cranial nerves. All will need to be reattached to the new body.
We don't actually have a good way of repairing spinal cord injuries, however this is a highly active area of research. I expect this problem is reasonably likely to be solved in the next 30 years or so.
Some cranial nerves can already be repaired (sorta, we just encourage the body to grow new ones to replace the old one), but others can't and are also active areas of research.
Rejection will not be a problem, since the recipient is a clone. We've already tested this extensively with identical twins.
What would a society look like where this was normal?
We would have gigantic warehouses storing and keeping healthy ranks upon ranks of clones. Every 10 years or so we'd start a new clone from each person, so that there's always a clone of about the right age available. We'd dispose of the clones once they reach 40, so there'd be about 4 clones per person. At 5 square metres of floor space per clone, this would take up 20m of floor space per person. An average western city has about 50m of floor space per person, so the facilities to grow and handle these clones would take up about a third of our cities, and a huge percentage of our work force.
People would use their clones as surrogates, both for their actual children, and for their children's clones. They'd also likely use them for blood and organ transfers and medical testing.
Whenever someone suffers a grievous injury, or feels like their bodies getting too old and creaky they'd transfer into their clone who's between the ages of 18 and 28. In an emergency, when no such clone is available, they'd transfer into a younger or older clone. people would only die when their brain stopped working.
Rich people would have dozens of clones "just in case". Poor people might not have any, or the state provided health care system might guarantee a minimum of one clones every 30 years or so.
Is this ethical?
I'm usually a high decoupler. If nobody's hurt by this, why would it be bad?
In this case I remain a bit squeamish. Firstly we don't understand consciousness well enough to know if the clones are feeling anything. And there's be strong incentives to come up with BS arguments that they don't regardless of the truth.
Secondly I expect that even if we get there in the end, we'd have to make a lot of mistakes in the process, effectively torturing a lot of baby humans. A true omelas situation.
OTOH getting rid of old age is good. The question is, is it worth the cost?
Even if you think so, the majority of people are not high decouplers, and will be horrified when the program first starts. Any attempt to get this off the ground will likely lead to very bad things for societal cohesion, which is in and of itself a reason not to do this. Spend your weirdness points elsewhere.
I've created the following sheet to play around with estimating life expectancy from regular brain transfers: https://docs.google.com/spreadsheets/d/120SUIMLKFeUEzfG8NydSXf9_rGf7ROHcehUKDmUJwkw/edit?usp=sharing.
It uses the Gompertz law to estimate the death rate at a given age.
It's got 4 variables you can play around with (copy the sheet to edit them):
1. Body age at which you undergo the brain transfer.
2. Age of the clone
3. Risk of the procedure
4. Increased mortality rate post proc compared to the expected baseline for the clones age.
According to the numbers I plugged in, we would see life expectancy of around 120 if we switched at age 50. We get best life expectency by switching at age 70, but that's an artifact of the simplified model, where transferring at a higher age doesn't increase risk past that point.
The variable that causes the greatest impact on life expectancy is how much transferring to a younger body reduces risk. This is also the hardest question to answer unfortunately.