Many people new to healthy life extension look at the projected future of regenerative medicine, stem cell research and tissue engineering and say "hey - why do we need all the rest of this science and hard work yet to be done? Why can't we just get all the way to rejuvenation with ever-improving stem cell medicine and parts replacement as needed?" An example of this sort of thought process showed up as a reprint at the LEF News recently:
The search for the fountain of youth is an old one, but it looks like scientists may just have found the real deal, at the tip of a syringe.
No, we don't mean plastic surgery - that's just looking like you'll live forever. What we're talking about is space-age regeneration, and they do it with stem cells.
Unless you live under a rock, you already know that scientists think stem-cell research will provide treatments for cancer, Parkinson's disease and spinal-cord injuries. But here's where you really start to care: It also has the potential to reverse the aging process.
Hypothetically, yes, pretty much everything except your brain is open to replacement just as soon as scientists can figure out how to build and install those replacements in a useful manner. That's a high bar, however. Your body isn't easily divided into piecemeal components; it's an overlapping bundle of interlinked, complex components - age-related damage to one system may make many related replacements useless or even counterproductive. Developing the technology base for safe replacement of the entire aging body is a long term project - not impossible, but certainly not something that you'll be seeing any time soon.
What will come in the next two decades are commonplace, affordable (for suitable definitions of "affordable") replacements for commonly failing organs and tissue types - new heart muscle, new liver cells, new dopamine neurons, and so forth. Many people will benefit and live modestly longer as a result, but while this first step into the world of replacement parts is underway, your biological systems will still be aging. Your immune system will still be becoming ever more frail, your telomeres shortening, free radicals spreading their damage, chemical junk building up within and between your cells, risk of cancer increasing - and most importantly, wear and tear growing in your brain.
What, then, will be the causes of age-related death 30 years from now? The body is an exceedingly complex machine; blocking off one failure mode, or preventing a single mode of death that results from a class of accumulated damage will leave many other possibilities. Behind the neurodegenerative diseases we know lie a hundred, a thousand ever more subtle and devilish ways in which age-related cellular damage can kill us. You can plug as many holes as you like, but eventually you're going to run out of fingers.
We can plausibly look forward to sidestepping this problem of ongoing damage by replacing an old heart with a young, tissue engineered heart lacking age-related damage. We are within a decade or two of being able to do the same for any other organ or system within the body ... but not the brain.
This prospect of unending discovery of new failure modes - and the long development of a cure, all too late to save those unlucky enough to be at the head of the queue - is one of the reasons that an engineering approach to fixing age-related disease is so attractive. Rather than play catch-up and research with ever more complex consequences of age-related cellular damage, let's identify, repair and prevent that damage. Strike at the root, in other words, by taking the path of greater effectiveness and least complexity. If we can do that, there would be no need to determine and decipher the fatal neurodegenerative conditions that follow Alzheimer's - no-one will ever accumulate the damage required to suffer from these presently unknown killers.
Your great-grandchildren may well live in a world in which bodies are like cars: built well, and discarded with regret when they have passed their prime, exchanged for new models. If we are to live to see that world, however, we have to take smaller first steps in the fight to defeat aging. The stem cell technologies of the next few decades are but one part of the technology base needed to repair the aging human body and brain.