Today’s open access commentary is intended to provoke discussion on the topic of how aging is thought about and presented, particularly at the intersection between the scientific community and the rest of the world, or between scientific disciplines, or between scientists and funding institutions. It is an interesting read, as such commentaries often are.
Aging, of course, exists. It is a useful word that is applied as a bucket to hold a very complicated, ever-changing, and still comparatively poorly defined set of degenerative processes and the consequences of those processes. We age, we decline. That much is evident and right in front of our eyes. So a term will be invented and applied to it; we humans are nothing if not ruthless taxonomists.
In another sense, however, there is no such thing as aging. Aging is a fiction, like all abstractions, and it is frequently counterproductive to try to deal with the bucket rather than the inconveniently complex contents of the bucket. Focusing on an abstraction will lead one astray and distance one from the reality of the situation. That may well have been fine and possibly even helpful in the past, but it could be harmful at a time in which it is becoming possible to address the mechanisms that make up aging, to slow and reverse the consequences of those mechanisms.
Some years ago, it was argued that aging is not a biological phenomenon. The argument – that there are not necessarily common mechanisms underlying the major aging-related chronic diseases, such as cancer, but rather a suite of individual disease processes synchronized via natural selection – would surely find little favor today. Common mechanisms, including inflammaging, mitochondrial dysfunction, and cellular senescence, are now thought to be well established. In retrospect, the argument seems ignorant of aging mechanisms. Here, we argue that this apparently ignorant view is right, but for the wrong reasons: that our more detailed knowledge of aging mechanisms is increasingly showing that there is no unitary phenomenon usefully summarized with the word aging.
What is aging? This question, at the heart of our field, has received a great deal of attention, and many definitions, implicit or explicit, have been proposed. (Here, we use the term “aging,” though all our arguments equally apply to the term “senescence,” which is favored by some). A coherent definition is even essential for the field: there are intensive efforts to measure aging, to slow aging, and to treat aging, and it will be impossible to know if they are succeeding without a clear definition of the subject of our research. Is it accumulation of molecular damage? Is it loss of function with increasing age? Is it increases in mortality (or decreases in reproductive rate) with age? Underlying the discussion to date is an assumption so basic it goes unnoticed: that there is an underlying biological phenomenon of aging.
We have a word for aging, and therefore we assume that science will accommodate us, providing a phenomenon to match our word. And in a colloquial sense this is certainly the case: no one can doubt that we see ourselves, our relatives, and our friends age. But is this colloquial usage scientifically justified? Is there really a “thing” or a phenomenon we can call aging? We argue here that our understanding of the biology is now sufficient to say definitively that this is not the case, that from a scientific perspective there is no such thing as aging, but rather a collection of disparate phenomena and mechanisms – sometimes interacting with each other – that relate in one way or another to our colloquial sense of the word. Accordingly, our desire to find a single reality of aging has created a great deal of confusion in the field.
We are well aware that not all researchers in our field will like our thesis here: our identity as “aging researchers” is tightly wrapped around the notion that there is a phenomenon of aging. However, we do not believe there is a need to feel any existential threat from this idea, which is in some sense a natural extension of the multi-factorial hallmarks of aging or pillars of aging framework. Rather, we think that being more careful about our underlying assumptions, and how they do or do not conform to biological reality, can only make us better researchers. The field of aging research can still exist, but with a more nuanced understanding that we are not studying a single biological phenomenon, but an assortment of loosely related processes that we find convenient to lump together.