(extremetech.com - Dr. Jan Vijg of the Albert Einstein College of Medicine has made a heavily qualified assertion that the maximum human lifespan is 115 years, plus or minus a bit. It’s a trend-based analysis, an examination of the global lifespan data as it stands. Since the data don’t show anyone living past about 115, with a very few notable exceptions, Vijg says that the data “strongly suggests” that 115 represents a hard limit to human longevity. He goes on to muse that human lifespan is “constrained by the myriad of genetic variants that collectively determine species-specific lifespan.” One hundred fifteen is a ceiling he doesn’t think we’ll break through.
I might be less bothered by Dr. Vijg’s claim if he had stuck with saying “Humans don’t live past 115,” rather than going on to imply that they can’t. Right up there with the inverse error and the availability heuristic, Vijg confuses correlation with causation, and in that way claims too much. Sure, we observe the trend that the shelf life of a human appears to top out at a century, plus or minus some depending on record-keeping. But that doesn’t mean we can say that genetics dictates humans can’t live longer than 115. We just don’t know why they don’t.
Vijg makes a classic logical error called cum hoc ergo propter hoc, just like the example of the relationship between ice cream sales and homicide rates. Ice cream sales and murder rates peak at about the same time each year. This means they’re correlated. But does ice cream actually have anything to do with murder? Not unless you get between me and my Cherry Garcia.
No, seriously, the reason is something else, a variable not accounted for when comparing only the two rates with respect by time. It’s awfully hot in the summer. Hot enough to get under your skin and make you uncomfortable, irritable, and sometimes downright irrational. Some people go buy ice cream. Some people go a-murderin’. Both rates hinge on how heat influences human behavior: a third, unseen factor, hiding in plain sight behind the date.
In this case, there appears to be at least one such unseen factor: DNA. Right now the human genome is “like a book elegantly bound, but in a language that you can’t read just yet.” There appear to be reasons in the human exome for the way we age, but they’re not programmed in; they’re more like the inevitable consequence of the way the system developed. Debris build up in cells over time until the cells die. Whenever DNA replicates, it appears to lose a bit of its end caps (telomeres) to the process. It’s called senescence. We don’t know how to stop it. We’re still fumbling our way through genomics, and while we’re zeroing in on telomeres to understand what they do and how they do it, we aren’t good enough at genomics yet to let our gene tech out in the wild. Gene therapy is still in its infancy, and telomeres aren’t a magic bullet for longevity either.
Ultimately, Dr. Vijg just doesn’t seem to be paying much attention to any of the recent research advances concerning human longevity, and he doesn’t attempt to present an explanation for the ceiling on longevity that he proposes — that is, beyond a hand-waving assertion that longevity is hard. What he says can be boiled down to “I see a trend in the data and have no explanation for why it’s there.” Again, this study is a trend-based analysis, which is more like what an umpire does — call the tableau as he sees it — than it is like any sort of prognostication or diagnosis. Speculation on why the trend is doing what it’s doing is just that: speculation.
Nevertheless, the study has a point.
The authors contend that the best way forward for our species, in terms of dignified and pleasant aging, is not necessarily to extend our life span. Vijg believes that extending the human health span is much more important. Instead of extending the human life span to 100 years and only having the first 65 or so being really good, the authors put forth the idea that the number of years is less important than how many of one’s years are healthy and enjoyable. There’s a valuable insight in the myth of Tithonus, who was granted immortality but not endless youth, and just withers away forever. It would be deeply unpleasant to just keep aging into a dessicated, Crypt Keeper-like husk, conscious and yet unable to participate. As the saying goes, it’s not about the years in your life; it’s about the life in your years.
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