This is the second volley of opinions on this topic between Dr. Kirkwood and myself. Please take a careful look at exactly what Kirkwood and I said in this exchange. Truth be told, my friend Tom needed to work hard to devise a line of reasoning to support the position he agreed to defend, but you don’t have to read between the lines to determine that in the final analysis, neither of us think that anyone alive today will live for 200 years.
So take heart, no one reading this needs to worry that anyone in their portfolio will experience radical life extension — the chances of this occurring are so remote that you’re more likely to get hit by a meteor. There will be medical advances to be sure, and therapeutic interventions that slow aging are on the horizon (I’ll talk more about that in a subsequent newsletter), but the timing of death is so consistent that overall it is now and will remain highly predictable for existing life settlement cohorts.
Keep in mind that in order for the life expectancy of a population to rise to 85 as we found plausible 31 years ago in our Science article, about half of the population must live beyond age 85, and a sizable proportion of each birth cohort must live into their 90s and even 100+. These people are called “super agers” — many of our clients have seen us mention this term during our reviews. Identifying who is most likely to fall into this long-lived subgroup of the population (we also call them right-tail survivors) is our specialty at Lapetus since several of us study Super Agers as part of our ongoing research apart from our work on Lapetus life settlements.
Dr. Tom Kirkwood
Dr. Olshansky asserts that there is no sound biological basis for suggesting that such a possibility is conceivable. I disagree. A basis surely exists in that longer-lived animals achieve their longevity through enhanced functioning of the molecular systems for cellular maintenance and repair. Further enhancement of these systems in humans is at least conceptually possible. I agree with Dr. Olshansky, however, regarding the near impossibility of doing it fast enough to answer the question raised here with a yes.
Being optimistic by nature, I expect significant improvements in healthy aging in the coming decades. Nevertheless, I see challenges that convince me that these improvements will not extend to 200-year lifespans any time soon.
The first challenge is the species problem. The lifespan modifications in other species have been made in animals much shorter lived than humans and which often manage their life cycles in different ways. We might hope that what works in them will work similarly in us, but until we have proved it, we should beware assumptions. Medical research uses animal models, of course, but many treatments that proved hopeful in other species have failed to work as well, or at all, in humans.
To date, there is no intervention with proven effects on the maximum length of human life. Since the proof of life extension potential will need demonstration in humans, the second challenge is of timescale. Imagine a clinical trial of a treatment believed to offer extension to 200 years. An anti-aging drug is most likely to be effective if taken before the aging process has wrought too much damage, say at age 50. The wait will be long.
Ethical and practical considerations also urge caution. We do not yet know what precise mechanisms we will need to target, but the likelihood is that they will involve fundamental processes of cellular maintenance. Modifying such processes is likely to cause side effects, raising at least the possibility of adverse reactions. Furthermore, this would be a treatment given to young, healthy adults, rather than those seeking alleviation of disease.
So, should we give up on the quest for longer lives? Absolutely not! We have every reason to expect the science to deliver real benefits. I believe, however, that we should not put lifespan itself so high in our wish list. The experience of seniors is that age is often not too bad, but that there is room for improvement. Let us work on that improvement, to make the most of the extra longevity we gained already.
Dr. S. Jay Olshansky
Lapetus Solutions and University of Illinois at Chicago
Dr. Kirkwood and I agree.
Without genetic programs for aging or death, therapeutic interventions that modify aging are possible.
Aging modification has already been accomplished in other species; it will likely be successful in humans.
Aging science is so promising that it should become a public health priority.
Investments in and funding for aging science have increased dramatically; they will accelerate.
It is not possible to test or prove an intervention purported to yield a human lifespan of 200 years.
A 200-year lifespan will not happen in these bodies, with current technology.
It’s true, other animals (e.g., the Greenland shark) and another mammal (e.g., the bowhead whale) live at least 200 years. This means evolution has already manufactured highly efficient cellular maintenance and repair mechanisms that scientists should be able to emulate as a therapeutic intervention. Would such interventions yield radical life extension in humans? I suggest the answer is no.
The problem is biological time. Mice live ~1,000 days, humans live ~29,000 days, and bowhead whales live ~76,000 days. A human-centric measure of time is applied to species that experience biological time at different rates than humans. A day in the life of a human is equivalent to a month in the life of a mouse; and a day in the life of a bowhead whale is equivalent to two days in the life of a human.
Benjamin Gompertz knew this in 1825 when he posited a universal “law of mortality”, and Raymond Pearl and other scientists controlled for biological time in experiments in the early 20th century using survival data from different species. When biological time is controlled for, length of life of different species is hypothesized to be equal.
In 1992 my colleague and I used survival data from humans, dogs, and mice, and found strong evidence that Gompertz and Pearl were right. We stretched clock time for life’s duration for a mouse and dog to resemble that of humans and found that developmental and biological milestones for all three species, including duration of life, overlapped. Evolution allocated different species roughly equivalent amounts of biological time!
This means that an intervention that extends life in a mouse should have a fractionally smaller impact on life extension in longer-lived humans. Dr. Kirkwood acknowledges that interventions that work in shorter-lived species do not have the same effect in humans. I believe variation in biological time is the reason why.
Without verifiable methods of achieving radical life extension and given that life expectancy has approached a point of diminishing gains, the time has arrived to declare victory in humanity’s quest for lifespan extension. I’m not suggesting we give up our quest for longer lives, especially given the presence of low hanging longevity fruit based on disparities and unhealthy lifestyle choices that can be reduced.
I do suggest that the focus of aging science and aging interventions should be on healthspan extension rather than radical lifespan extension; and speculating on a 200-year lifespan for humans is best left to science fiction.