If all of a hydra's cells are replaced every four weeks, I would say that the hydra has a life span of about four weeks. Ship of Theseus and all that.
But even if you don't subscribe to that particular view of what constitutes a consistent identity, the issue is still fundamentally thermodynamic. It is not a task of just maintaining a particular dynamic system indefinitely, but maintaining one with memory. If the hydra is storing absolutely no information about its past states, then it isn't evolving, and it is completely at the mercy of its environment. This makes it more akin to fire or a piece of iron rusting than life: just a consumptive chemical process. This harmonizes exactly with your last paragraph, things need to store some amount of memory of past failure if they are to adapt. This storing process is exactly aging, but how it manifests in different organisms can obviously be very different. Landauer's principle, then, tells us that since information is thermodynamic, so too must be aging. However, I don't really think the author of the original article was arguing at that deep of a level. In humans, many of the processes that we consider to be the detrimental effects of aging do occur because the components that make us do have memory effects. One particular example would be the cross-linking of elastin, causing degradation of vascular system efficiency.
But aging truly is an inevitable consequence of thermodynamics, it's just that since everything is a consequence of thermodynamics, it's not a particularly illuminating argument.
> If all of a hydra's cells are replaced every four weeks, I would say that the hydra has a life span of about four weeks. Ship of Theseus and all that.
Most of our cells in our bodies are renewed in a few months or something. Yet people don't assimilate this to death.
Now, you may object that neurons don't follow this rule, so our subjective identity is not concerned by this. To this I will say that when people are concerned about ageing, they are indeed concerned about what happens to their brain (that is, neuro-degenerative diseases), but certainly not only that. The state of all the other tissues is at stake : the heart, the bones, the skin and so on. Yet all of these are renewed on a regular basis. That renewal is not perfect though, and it's that imperfection they blame on ageing.
But even if you don't subscribe to that particular view of what constitutes a consistent identity, the issue is still fundamentally thermodynamic. It is not a task of just maintaining a particular dynamic system indefinitely, but maintaining one with memory. If the hydra is storing absolutely no information about its past states, then it isn't evolving, and it is completely at the mercy of its environment. This makes it more akin to fire or a piece of iron rusting than life: just a consumptive chemical process. This harmonizes exactly with your last paragraph, things need to store some amount of memory of past failure if they are to adapt. This storing process is exactly aging, but how it manifests in different organisms can obviously be very different. Landauer's principle, then, tells us that since information is thermodynamic, so too must be aging. However, I don't really think the author of the original article was arguing at that deep of a level. In humans, many of the processes that we consider to be the detrimental effects of aging do occur because the components that make us do have memory effects. One particular example would be the cross-linking of elastin, causing degradation of vascular system efficiency.
But aging truly is an inevitable consequence of thermodynamics, it's just that since everything is a consequence of thermodynamics, it's not a particularly illuminating argument.