Evolution Predicts that Humans Should Not Suffer Infirmities of Aging
When describing what makes a proposed theory a good theory, Stephen Hawking said "[a] theory is a good theory if it satisfies two requirements: It must accurately describe a large class of observations on the basis of a model that contains only a few arbitrary elements, and it must make definite predictions about the results of future observations." Other academicians have described the second of Hawking’s tests as perhaps the defining characteristic of all scientific knowledge -- the ability to make falsifiable or testable predictions.
The purpose of the scientific method is to create a conceptual framework, or theory, that explains not just what happens, but why it happens. That framework or theory can then be used to predict what will happen in the future. Take the apocryphal example of Newton developing the Theory of Gravitation based upon the observation that an apple falls from a tree. The Theory of Gravity explains why the apple falls rather than rises. Once we know why the apple falls, we can predict that all other apples will also fall. We’re not relying on the previous observations; we are relying on the Theory.
If the next apple doesn't fall, we call it an anomaly. An anomaly is an empirical result that is different from what the theory predicts. If we can’t come up with an adequate explanation for why the anomaly occurred, it means that the underlying theory is flawed.
As noted elsewhere in this website, all previously proposed theoretical explanations for why humans lose function with the passage of time are riddled with unexplainable anomalies. Thus there is no generally accepted theory of aging. All we have to rely upon are observations. Historically everyone loses function as they age; therefor scientists have concluded that losing function with age is inevitable. But in the absence of a theory, we don’t know why. And if we don’t know why, we can’t be certain that the next person won’t retain or improve functionality as he or she ages.
There is one very powerful life sciences theory that does address the issue of loss of function. That’s the Theory of Evolution. And it predicts that humans should not lose function as they age.
Natural selection works by selecting traits that enhance the probability of an organism surviving and reproducing. What trait could be more important for survival and reproduction than functionality? The progressive dysfunctionality that characterizes the infirmities of aging could not be a trait that would be favored by natural selection.
Evolutionary theorist George Williams wrote: "It is remarkable that after a seemingly miraculous feat of morphogenesis, a complex metazoan should be unable to perform the much simpler task of merely maintaining what is already formed." Similarly, biogerontologist Aubrey de Grey wrote that the aging process is paradoxical because “it seems obvious that the maintenance of a complex machine in a fully functional state is a vastly simpler problem than the construction of that machine, so evolution, having mastered the latter, should find the former a doddle.”
In order for natural selection to choose continuing functionality over progressive dysfunctionality, a maintenance process would have had to be a viable option. That’s why Williams and de Grey observe that a maintenance process would be simpler than the initial growth process. Humans also have immune systems and healing processes. Since a maintenance process would be no more difficult than any of these other processes, academicians generally concur that evolution could have given us a maintenance process that would prevent the infirmities of aging.
A process that maintains functionality as we age was an available trait. That means that evolution had a choice between maintaining functionality and losing functionality as we age. Everything we know about evolution tells us that maintaining functionality would have been the trait favored by natural selection. But all humans lose function as they age. That’s a pretty big anomaly. Either there is an acceptable explanation for the anomaly, or the Theory of Evolution is seriously flawed.
Efforts to explain the anomaly have focused on the later stages in human life. Some scientists look at aging as an aspect of death. Alternatively, there is the evolutionary neglect hypothesis, which posits that once a human has reached reproductive maturity there is no compelling evolutionary need for a genetic maintenance program. But there is a huge problem with these rationalizations.
The “aging process” is the accumulation of years of damage at the cellular level that commences in the typical human early in the third decade of life, i.e., in his or her 20s. Medical science may not take notice of such damage until it shows up as a major disorder decades later, but that’s not how the body works. The body doesn’t wait until a minor cut festers and turns into a life threatening infection before it activates the healing process. The body doesn’t wait until an invading microbe causes a life threatening disease before it activates the immune system response. The optimal time to address a threat is at inception. Thus, the Theory of Evolution doesn’t just predict that we would have a maintenance process, but that we would have one that would be active and repair damage that starts occurring when we are still in our 20s. Rationales that focus on the later stages of life cannot explain away the anomaly.
The proposition that natural selection would not have favored a maintenance process that would repair minor damage is so at odds with expectations that many academicians argue that the maintenance process could not have been an option. That school of thought also focuses on the later stages of life and whether or not it is possible to sustain life or health indefinitely. But this school of thought also ignores the fact that the "aging process" has nothing to do with the later stages of life. The damage commences when we are still quite young, and that's when the maintenance process would kick in. What may or may not be possible for someone in his or her 60s or 70s is irrelevant.
In this regard, it is important to understand that repairing damage is not necessarily an all or nothing proposition. The maintenance/growth process does take a lot of energy, and throughout evolutionary history, limited fuel has been a concern. So natural selection was confronted with choices. But the choice was not a choice between repairing all damage in old people and no process at all. The choice was between repairing cosmetic damage and damage that would ultimately lead to dysfunctionality in critical processes.
The Theory of Evolution predicts that humans should have a maintenance process that would prevent infirmities. All of our historical observations indicate that humans do not have such a process. There appears to be no satisfactory explanation for the anomaly. Does this mean that the Theory of Evolution is seriously flawed?
No. The problem is the unstated assumption. Everything in the foregoing discussion assumes that humans are exactly what we are genetically designed to be. The Theory of Evolution predicts genetic potential, not phenotype. As predicted by the Theory of Evolution, all humans are genetically endowed with a Growth Process (a process that is even more powerful than the maintenance process that the Theory of Evolution predicts). But that process must be activated. What we are – phenotype – is heavily influenced by environment. Human civilization has allowed us to vary our evolutionarily normal environment. Human adults are not compelled by the forces of nature to engage in the frequent intense exercise that activates the maintenance/Growth Process. The Theory can't be blamed for our failure to take advantage of the Growth Process.