but I don’t think it would extend lifespan indefinitely.
I think the big question about head transplants for me is how it interacts with the process of aging, given that body systems are heavily intercorrelated and damage in one system will damage other systems (and vice versa with healing).
Intuitively, I would expect it to work statistically in one of two ways. In the pessimistic case, the brain keeps aging on the normal Gompertz schedule, and even a perfect head transplant can never buy you more than a decade or two before any of your head-located diseases kill you; it corresponds to shifting the aging mortality spike down somewhat, but it is still going to spike soon. (In this scenario, the trauma and cost of a head transplant might rule it out for a lot of elderly people: you might die on the operating table or afterwards, and it doesn’t buy you much time.) In the optimistic case, the near-reset of the body to the pink of youth will eliminate all of the aging acceleration from the rest of the aging body and heal the brain and by changing the exponent, potentially buy you drastic increases in lifespan by flattening the spike, and 50 or 100 years might suddenly be statistically plausible. At which point you might as well consider it an indefinite lifespan extension because who knows where medical technology will be in 100+ years?
I think the big question about head transplants for me is how it interacts with the process of aging, given that body systems are heavily intercorrelated and damage in one system will damage other systems (and vice versa with healing).
Intuitively, I would expect it to work statistically in one of two ways. In the pessimistic case, the brain keeps aging on the normal Gompertz schedule, and even a perfect head transplant can never buy you more than a decade or two before any of your head-located diseases kill you; it corresponds to shifting the aging mortality spike down somewhat, but it is still going to spike soon. (In this scenario, the trauma and cost of a head transplant might rule it out for a lot of elderly people: you might die on the operating table or afterwards, and it doesn’t buy you much time.) In the optimistic case, the near-reset of the body to the pink of youth will eliminate all of the aging acceleration from the rest of the aging body and heal the brain and by changing the exponent, potentially buy you drastic increases in lifespan by flattening the spike, and 50 or 100 years might suddenly be statistically plausible. At which point you might as well consider it an indefinite lifespan extension because who knows where medical technology will be in 100+ years?