In Tolkein’s Lord of the Rings (LOTR) the elves are immortal in the sense that they do not die of old age. They can, of course, be killed by accidents or in battle, be murdered, etc. Man, by contrast, is “doomed to die”, the phrase that appears in the poem about the Nine Rings that opens the novel. Of course, JRRT had a Christian perspective, and viewed an inherent mortality as a planned condition that is part of a scheme to save humankind from a worst fate that would await him if death did not deliver him from the corrupting evils of a “fallen world”. It presumes a sort of “planned obsolescence” that would pave the way for a second life that would, presumably, be free from such spiritually corrupting influences.
Well, me, while I love the mystery and the strange ambiance of LOTR, I don’t know anything for certain about any such second lives. For one thing, I cannot imagine what reality such a second life might be like, and in particular how it might be free from the potential for evil. But this is a complicated issue, to say the least, and it is not what I want to dwell on at the moment. Rather, all this leads me to thinking: what is the scientific reason for the human body ageing and, on a time scale of-- for most of us--- “four score” (80 years), rather rapidly wearing out and dying of “old age”? (if something else doesn’t get us first, of course.)
I always look at such issues from the game theory perspective of evolutionary biology. And it seems to me that the situation of Tolkein’s elves suggests the reason for the body wearing out and the body’s processes grinding to a halt. Namely, there is some expectation value of elapsed time before an accident causes death, and nature does not want to waste any efforts in assuring that the body and mind will last much beyond that average time interval. By the way, by “accidental death” I mean to include all of the causes of death that are not associated with the total body simply wearing out. That is, everything except “dying of old age”.
It is often noted that once the organism has produced offspring, and has ceased being fertile, we can expect it to be on borrowed time for some interval after that. But this begs the question. Why is fertility of finite duration? I suspect that the answer is again, that there is little to be gained by engineering a body that can continue to reproduce for a time that greatly exceeds the temporal expectation value for accidental death.
The wikipedia page on fertility in both human males and females has, in this regard, an unsatisfactory section called “the cause of the decline”. But the title of this section is incorrect because it really just deals with the statistics on when fertility falls off. In other words, it does not address what the real cause of the decline is.
I want to add---perhaps unnecessarily—that when I speak of such things as “nature engineering something” I do not mean that I impute conscious design to any entity outside of nature, or to nature herself. I view this in a Smithsonian sense as being one of those phenomena under the control of an invisible hand, and consider genetic evolution to be a sort of computer that through natural selection reaches an optimal solution.
I look forward to looking into the popular evolutionary literature on what is thought to cause aging and death. The above comments are really intended to simply raise the issue, and I plan to revisit the topic after I have done a bit of research. I noted today a chapter in J. Diamond’s book “The Third Chimpanzee” that speculates about the issue of aging, and I plan to read that first.