The car analogy that shows up most often in my circles relates to repair and the biological damage of aging. We, like cars, are machines. We differ only in complexity, and the same methods arising from reliability theory can be used to model progressive dysfunction and systems failure over time in both vehicles and people. Given sufficient tools and resources a car can be maintained in good working condition indefinitely, a Ship of Theseus pattern progressing forward into the indefinite future. This is something we could achieve now for any model of car in the world, but for the most part choose not to. The only reason we cannot presently achieve the same result for people is that we lack the tools, the rejuvenation toolkit outlined in the SENS research proposals, ways to repair the known forms of damage that distinguish old tissue from young tissue. In principle we could all become Ships of Theseus once rejuvenation therapies exist, with the unit of replacement being individual cells where the precise details of structure and molecular arrangements matter (largely in the brain) and anything up to whole organs elsewhere in the body. This is entirely possible and plausible, and given sufficient funding could arrive soon enough to matter for most of us.
This is the car analogy for rejuvenation research supporters, used as a way to help convince uninformed audiences skeptical about the prospects for prevention and reversal of aging. We can maintain cars, therefore it is reasonable to work on ways to maintain people. Insofar as thinking about maintenance goes, people and cars are basically the same class of entity. The rejuvenation research crowd are not the only set of folk thinking about extending life, however, and they are (unfortunately) far from the most numerous at this time. The majority of people inside and outside the scientific community with an interest in enhanced longevity think in terms of slowing aging and altering the operation of metabolism: incremental, small advances towards better operation of the human machine. In comparison to rejuvenation research vast sums are directed towards that goal, though it is still a very small field in comparison to medicine as a whole. As long-time readers will know by now, I think little of slowing aging as a goal: it is the expensive road to a near-useless end result. What good is slowing aging for those who are already old? Metabolism is fantastically complex and the prospects for significant progress in altering it to extend life are remote, judging by the time and money expended and lack of results obtained to date, and this is generally acknowledged as true by scientists in the field.
Outside the scientific community, people are more enthusiastic about the prospects to extend life by incremental advances in drugs, supplements, and other things I'd consider a pointless waste of time in comparison to the more serious modern applications of biotechnology in SENS research. These folk have their own car analogy, which is sketched in the post quoted below. It is a helpful read if you're looking to understand the mindset that has people chasing the mythical ever-better combination of supplements and prospective new ways to manipulate metabolism to slow aspects of aging:
Can we expect to live longer and longer as the first part of this century rolls by? I think so, probably by a large amount. Will this extension of human lives be because of basic new scientific breakthroughs? Yes, but only in part. Collectively, such breakthroughs are likely to be important. Curiously though, I don't think that any single such breakthrough will make an immense difference. What will matter is a process issue, and whether and how such breakthroughs are applied is only one consideration.
So, how then will it happen? I argue here that extended longevity is likely to happen via a number of incremental steps,probably small ones at that. Most will involve improvements in lifestyle and diet. Others will involve selective application of stresses and consumption of health-producing phytosubstances and selected dietary supplements. I think you can move along the increasing longevity curve by pursuing a long string of incremental lifestyle and dietary modifications over time, each of which may seem to produce only modest results. Some steps may seem to be very tiny and insignificant, such as getting up from the computer and walking around a bit every hour.
Let's start by talking about, my grandmother's 1950 Chevy Bel Air, purchased new. . If you were middle class and lived in Detroit you were expected to turn your car in every year for a new car, or at least every 2-3 years. Most cars did not survive the junk heap for more than 4-5 years. A three-year-old car was a seriously old car and you could expect to put less than 50,000 miles on it before it died. [In contrast, consider] our 2005 Subaru Impreza which we purchased in 2004. Expected lifespan: 15-20 years, perhaps 200,000 miles. This 10 year old car is still healthy, vigorous and a reliable family workhorse with no known problems at 100,000 miles. No sign of rust.
What was the big scientific or technical breakthrough that made the difference in lifespan and performance between the earlier cars and our Subarus? Lifespan extension of a factor of at least four and MPG improvement by a factor of two? None! In fact, it wasn't any single big scientific or engineering breakthrough. The difference is because of thousands of incremental improvements made year after year in just about every component and system. Virtually everything has been improved to make cars more reliable, last longer and operate more economically.
To be clear, I think it is arrant nonsense to state, as the author does above, that we could incrementally move to doubling our life spans without the application of modern biotechnology, interventions that meaningfully and directly repair cellular damage. Not diet, not drugs, not random compounds dredged from the natural world because they turn out to do more good than harm, but designed applications of molecular machinery that achieve specific goals in our biochemistry, reverting most or all forms of low-level damage in and between our cells. This is a night and day difference in goals, ambition, and methodology. If you had a perfect diet and lifestyle, you'd still mostly likely die before age 90 in the environment of today's medical technology - because it is medical technology that overwhelmingly determines your life span, not your lifestyle.
Putting that aside, the rest of the article actually has little to do with specific implementation details and is more concerned with a vision of organized incremental improvement in life span. It is long and worth reading as a matter of interest.