Something to think about for today: SENS, the Strategies for Engineered Negligible Senescence is not put forward as a theory of aging, but it is a theory of aging, one that pulls from many other partial attempts to explain aging. It purports to describe, as best we know, the detailed mechanisms that lie at the root of degenerative aging - but is presented (and currently running) as a program of research and development to reverse aging. That is the testable part of the theory, if you like: implement SENS and we should see rejuvenation. If this comes to pass, then it is true that SENS as laid out at present does describe all forms of fundamental damage that cause aging. If not, then SENS is either wrong or, more likely, incomplete - there is some other form of damage that is important and unconnected to those already discovered.
(No new form of fundamental change or damage related to aging has been identified in the past 25 years, across a time of raging progress in biotechnology, which should gives us some confidence that there are no others. There is always room to argue, however, and science is anything but static).
There are, it has to be said, a great many theories of aging. Following this line of thinking, it occurs to me that we can classify most theories of aging according to where they stand with respect to the hole we find ourselves in - that hole being the inconvenient fact that we're all aging to death, and progressively increasing suffering and pain lies in each of our personal futures.
I see three broad buckets for this hole-based taxonomy:
- How did we get into this hole?
- What is going on in here?
- How do we get out of this hole?
How did we get into this hole?
Evolutionary theories of aging seek to explain how we came to age the way we do. Here the proposed mechanisms of aging inform the discussion and modeling of plausible evolutionary processes that would produce them - as well as the staggering variety in lifespan and pace of aging that exists in the natural world. I see this as scientific dispassion at its finest: "Look at the interesting way in which we're all dying! Fascinating, no? We should take some time to think about how this came to pass."
What is going on in here?
Other theories of aging focus on modeling how aging happens: what are the exact mechanisms? Many different approaches to these theories exist. Consider, for example, those that describe aging at the high level, such as in the use of reliability theory to frame aging in the form of a systems failure model. At the other end of the room we have things like the mitochondrial free radical theory of aging, which proposes detailed and particular mechanisms in cells and cellular components that lead to damage and then the larger-scale manifestations of aging.
How do we get out of this hole?
So here we return to SENS, a meta-theory of aging that pulls from many of the mechanism-focused theories of aging proposed over the past century. Until the advent of SENS there really wasn't any sort of contingent in the scientific community whose members presented a theory of aging as something more like a theory on how to defeat aging - to prevent and treat aging with therapies, reverse frailty in the old by removing its root causes, and stop the young from becoming aged.
So we are in a hole, no arguing that. Getting out does require some understanding of the hole in order to best direct efforts - but the scientific community is far and away past the point at which we could be effectively working our way out. Spending all our time gathering more knowledge is no longer good strategy. We in fact don't need to know all that much about how we got here, nor exactly how fundamental causes of aging spiral outward to create the thousand and one causes of death we observe in old people. What SENS tells us is that we just need to know what those root causes are and how to fix them. Additional information is useful, and will probably improve efficiency, but it is not absolutely necessary and nowhere near as important as just forging ahead to get the job done. The test of SENS as a theory aging is for the research community to get out there and actually fix the problems that are killing us.