AGING IN OTHER SPECIES

“Discovery consists of looking at the same thing as everyone else and thinking something different.”

Albert Szent-gyorgyi

A foundational misconception of the aging paradigm is the presumption that biological aging is a unitary phenomenon that has the same root cause in all organisms. The Institute acknowledges that the primary symptom of biological aging – the accumulation of intrinsic damage causing physiological deterioration that results in progressive dysfunctionality of all organs and systems – is the same in all mammals. Where the position of the Institute differs from conventional wisdom is that it posits that the accumulation of damage in humans has a different root cause than the age-associated accumulation of damage in other mammals.

Defining Terms

One of the recurring themes of this website is that much of the confusion surrounding aging is the failure to develop clear definitions of critical terms. The use of the term “aging” to describe the physiological deterioration experienced by both humans and other mammals makes the effort to distinguish between the two traits almost impossible. To avoid this problem, the Institute introduces different terminology. When referring to the declines in physiological performance suffered by all mammals as they approach the end of life, this website uses the term Natural Progressive Decline (“NPD”). When referring to the progressive declines in physiological performance suffered by a typical human commencing relatively early in life, this website uses the term Functional Decline Syndrome (“FDS”).

“Lifespan” means the period of time that, on average, the members of a species actually live. “Longevity” is the period of time that a member of a species is expected to live in the absence of aging-independent causes of death such as predators, starvation and non age-associated disease. This website introduces the term “natural lifespan” of a species to mean the period of time before substantially all members of that species necessarily die from aging-independent causes of death in the evolutionary environment.

Animal Longevity

The naked mole rat can live for more than three decades.

Aging theorists have long noted the fact that the longevity of otherwise similar species can vary remarkably. An obvious example would be rodents. Even under ideal conditions, the lab rat will rarely survive for more than a few years; by contrast, the longevity of the naked mole rat is estimated to be more than three decades. All mammals (including humans) were descended from a common ancestor. The only explanation for the extreme variances in longevity is that longevity is genetically determined and developed through an evolutionary process in a way similar to the one that determines other species-specific traits.

How high can a bird fly? The answer varies dramatically depending on the species of bird. Where the ability to fly at great heights conferred a substantial evolutionary advantage, mutations that led to that result (at a cost to other traits) were passed down to subsequent generations. Each species of bird has different capabilities with respect to the ability to fly. All such capabilities are determined by the physiological makeup of the species, which is determined by natural selection.

PA proponents argue that the only physiological process that could have evolved to explain the variance in longevity among species would be their hypothetical aging mechanism. Per the PA argument, all organisms must possess complex evolved mechanisms that exist for the purpose of pro-actively limiting the organism’s lifespan beyond a species-specific age.¹

The Institute agrees with PA proponents that the only way to explain longevity variances among species is through the evolution of a physiological system that determines longevity. Where the Institute disagrees with the PA proponents is in identifying the maintenance system as being the critical physiological system. A core hypothesis derived from the New Paradigm is that the longevity of any species is a function of the capabilities of that species’ maintenance system. Like all other physiological systems, maintenance systems evolved in very different ways in different species.

In Their Evolutionary Environment, Animals Don’t Age

In their evolutionary environment, all mammals die from aging-independent causes of death before they show any signs of NPD.² NPD occurs in animals only because human interference allows them to outlive the effectiveness of their maintenance systems.

Substantially all domesticated animals have for many generations been the subject of human-designed breeding programs. As a result, in addition to not being exposed to evolutionary environment, domesticated animals have, for generations, not been subject to the forces of natural selection.

Recent studies have found evidence of aging/progressive physiological deterioration in certain species in the wild. But the evolutionary environment is not the same as “the wild.” The effect of humans on the planet has been so pervasive that the current environment, even in the wild, is a far cry from the evolutionary environment. Human activities (e.g., hunting, pesticides such as DDT, etc.) have had a disproportionately adverse effect on predator populations. In the evolutionary environment, there would be a robust predator species for all other species. Animals tend to flock together not because they are going to protect one another (other than offspring), but rather to ensure that the least fit gets taken by predators.

The evolutionary environment is one in which each individual member of the species must acquire its own food and avoid/defend itself from a robust predator population. In an environment where predators are ubiquitous, and competing for sufficient food is a life or death challenge, symptoms of FDS – i.e., diminution in functionality – would likely prove to be fatal within a relatively short period of time. Human interference has altered the evolutionary environment by killing off a disproportionate number of predators, and domesticating and feeding many species. As a result, NPD appears to be a quite common phenomenon – domesticated animals typically outlive the natural lifespans of their species. Thus it’s not surprising to that the conventional belief is that NPD and FDS are the same phenomenon.

NPD in Mammals Is Consistent with the Theory of Evolution

A mammal that is protected from all aging-independent causes of death will nonetheless have a genetically mandated chronological limitation on longevity. Regardless of environmental factors, after some number of years, accumulating damage will cause progressive declines in physiological performance, and those declines will ultimately result in death. Those progressive declines are the genetically mandated natural phenomena that the New Paradigm labels NPD.

Longevity is a function of the capabilities of an organism’s maintenance system. Maintenance systems are no different than other physiological systems – each species has different capabilities resulting from millions of mutations over the eons. Maintenance processes require resources. Processes that operate at the tissue or organ level require far more resources than those that operate at lower levels of biological organization. All organisms have finite resources that must be allocated among competing traits. Since allocating additional resources to the maintenance system detracts from other survival traits, natural selection had to make choices. There is no evolutionary benefit conferred by an organism’s maintenance system functioning effectively beyond the natural lifespan of that species. Thus, the capabilities of the maintenance system of each mammalian species has a genetically established chronological limitation that is a function of the natural lifespan of that species. When an animal outlives its natural lifespan (and thus the chronological limitation on the effectiveness of its maintenance system), it begins to show age-related diminutions in functionality.

The common lab rat provides a simple example. In its evolutionary environment, over 95% of the members of the species die from non-age-related causes within the first year of existence. The number that survive even a second year is infinitesimally small. An enhancement of the rat’s maintenance system (e.g., an organ level maintenance process) that would extend its longevity beyond a few years would be of no value, because in the evolutionary environment, the rat would inevitably die from an aging-independent cause before the trait became relevant. There would be no selective pressure to retain those genes. So the natural lifespan of the species is about two years. However, if protected from predators and provided with food, a lab rat will outlive its natural lifespan. A lab rat will show no diminution in functionality during its first couple years of life. But, having outlived its natural lifespan (and thus the chronological limitation on the effectiveness of its maintenance system), it starts showing progressive diminishment in functionality after its second year.

Contrast the lab rat with the naked mole rat. The naked mole rat is notable for having a lifespan that can exceed three decades. The naked mole rat evolved in an environmental niche that was protected from predators. Thus life-extending mutations to its maintenance system did confer evolutionary advantages; those traits were favored by natural selection and became part of the naked mole rat genome.

Chronological limitations on the effectiveness of their maintenance systems may appear to be detrimental to lab rats or other domesticated animals. However, if those limits are never reached in the evolutionary environment, then allocating finite resources to physiological systems other than the maintenance system is a choice that benefits the organism. Thus it is consistent with the theory of natural selection that when removed from the evolutionary environment, once an organism survives beyond the natural lifespan of its species, its maintenance system is no longer effective. That ineffectiveness allows for the accumulation of intrinsic damage, which results in NPD and ultimately in death.

Distinguishing NPD from FDS

The Institute acknowledges that the primary symptoms of mammalian NPD and human FDS – physiological deterioration caused by the accumulation of intrinsic damage – are identical. It is also true that in both cases the accumulation of intrinsic damage is caused by the ineffectiveness of the pertinent maintenance system. However, the Institute is of the view that NPD and FDS are not the same phenomenon because they have different root causes. NPD is a natural consequence of chronological aging: FDS is not. For these purposes, the term “natural” means genetically mandated regardless of environmental factors.

The root cause of NPD is a natural chronological limitation on the effectiveness of mammalian maintenance processes. The root cause of the FDS suffered by most humans at a relatively young age is that an environmental agent is preventing the human maintenance system from performing up to its capabilities.

The fact that in the evolutionary environment, no mammal shows any signs of diminished physiological performance is compelling evidence that all mammals have maintenance systems that remain effective (with “effective” meaning preventing any diminishment in physiological performance) throughout the natural lifespan of the organism. That result is exactly what is predicted by the principles of natural selection. Since diminished functionality would prove to be fatal in the evolutionary environment, any enhancement to an organism’s maintenance system that would ensure optimal functionality during the natural lifespan of the species would be selected. But enhancements that would improve effectiveness beyond the organism’s natural lifespan would confer no evolutionary advantage and would be rejected.

Thus, no human should manifest any symptoms of FDS until the subject has exceeded its natural lifespan. That raises the question – what is the natural lifespan of a human? If the natural lifespan of a human were only 19 years, then, as is conventionally assumed, FDS and NPD would be the same phenomenon. If, on the other hand, the natural lifespan of the human species is, as the Institute posits, in excess of 70 years, then FDS is a disorder of monstrous proportions. The “natural lifespan” of a species is the period of time before substantially all members of the species necessarily die from non-aging related causes in the evolutionary environment. In the modern environment, there is no time certain when all members of the human species would necessarily die from non-aging related causes. But what about the evolutionary environment?

In other words, in order for FDS to be a manifestation of NPD, the natural lifespan of a human would have to be about 20 years. But in a typical human, the maintenance system continues to function (albeit at a suboptimal level) for more than 50 years after physiological impairments of FDS become noticeable. That fact is compelling evidence that the natural lifespan of humans is significantly more than 20 years.

The preconception that NPD and FDS are the same phenomenon is so pervasive that empirical evidence relating to both are (mis)interpreted in a manner that accommodates that assumption. The aging paradigm frequently utilizes an empirical model that assumes that all young humans are healthy and strong. Old people are unhealthy and weak. A human grows until she reaches a physiological peak at about the age of 20. The body remains at that physiological peak for some number of years or decades. But inevitably it begins to age, perhaps commencing in the fifth decade. The aging process is assumed to encompass all of the physiological changes that occur thereafter. Those changes involve a steady, irreversible decline in all physiological functions, ultimately resulting in death.

If that empirical model were accurate, then FDS would be quite similar to NPD. Once a domesticated animal outlives the chronological limitations of its maintenance system, it does experience a steady, irreversible decline in all physiological functions, ultimately resulting in death. But the aging paradigm’s empirical model does not represent reality for humans. The accumulation of intrinsic damage that results in FDS doesn’t just happen to old people; it’s noticeable while humans are in their early 20s. In fact, diminished physiological performance is so pronounced in younger humans that the onset of aging (i.e., diminished physiological performance) in humans is frequently correlated to “reproductive maturity” (about the age of 19) rather than “later in life.”

But in order for FDS and NPD to be the same phenomenon, then all mammals would also manifest symptoms of FDS soon after they were initially able to reproduce. That’s simply not true. The reality is, as discussed above, in the evolutionary environment, mammals never exhibit any signs of FDS. We do see older domesticated animals that are suffering the infirmities of aging. But those signs do not appear within a short period of time after they are initially capable of reproduction. Those infirmities begin to appear only after those animals have exceeded their natural lifespans.

Another distinction between FDS and NPD is that NPD is a trait that is shared by 100% of the members of a given species regardless of environmental conditions. Once any member of a particular species has exceeded the natural lifespan of that species, it will start to show symptoms of NPD. But FDS does not begin to appear in some humans until very late in life. Many people who are now in their 50s and 60s are healthier and stronger than they, themselves, were decades earlier. The only way an older human can avoid the accumulation of damage that would otherwise result in a diminution in physiological performance is by having a fully effective maintenance system. But the effectiveness of the maintenance system of any mammalian species is limited by the natural lifespan of that species, and no individual member of the species can exceed that limit. Thus, the existence of humans in their 50s and 60s who have effective maintenance systems is compelling evidence that the natural lifespan of humans is far greater than 20 years.

Conclusion

Longevity variations between similar species must be the result of the evolution of physiological systems. In order to validate the preconception that all species have specific aging mechanisms, PA proponents argue that that aging mechanism is the only possible candidate for such a system. But in order to do that, the PA paradigm (as does the NPA paradigm) simply assumes that maintenance systems are either non-existent or inherently ineffective. But even if an aging mechanism did exist, PA proponents cannot explain why different species age at different rates. By acknowledging the existence and significance of maintenance systems, the New Paradigm provides a far better conceptual framework for explaining that anomaly than does the PA paradigm.

Goldsmith TC, On the programmed/non-programmed aging controversy, Biochemistry (2012).
Finch C.E., Longevity, Senescence and the Genome, Chicago University Press, (1990); Lack D, The Natural Regulation of Animal Numbers, Clarendon Press, (1954); Medawar P.B.,An Unsolved Problem of Biology, Lewis (1952). See also, Hayflick L, Entropy explains aging, genetic determinism explains longevity, and undefined terminology explains misunderstanding both. PLoS Genetics (2007).

This is the last essay in the section entitled “The Case for Paradigm Shift.” The next section is “The New Paradigm.”