The Oldest Question
Every human society has dreamed of escaping death. Gilgamesh sought the secret of eternal life. Ponce de León allegedly searched for the fountain of youth. Alchemists promised elixirs of immortality. The religious afterlives of every major faith are, at their core, solutions to the problem of death.
For most of history, these were fantasies. Death was inevitable, and extending life beyond a few decades required nothing short of miracles.
Then modern medicine arrived. In a single century, life expectancy in developed countries roughly doubled—from around 40-50 years to over 80. Most of these gains came from reducing early death: cutting infant mortality, treating infections, preventing death from childbirth and injury. Medicine didn't slow aging; it just helped more people reach old age.
But now the question changes. Having conquered many causes of early death, humanity faces aging itself—the gradual accumulation of damage that degrades function and eventually kills. And for the first time, aging is being approached not as an immutable fact but as a biological process that might be understood, modified, and perhaps reversed.
This chapter asks: How long might humans live? What would it take to extend not just lifespan (years lived) but healthspan (years lived in good health)? And what would a world of dramatically extended lives look like?
2026 Snapshot — The Science of Aging
What Aging Is
Aging is not one thing but many—a collection of biological processes that interact and compound over time.
The hallmarks of aging, as identified by researchers, include:¹
- Genomic instability: DNA damage accumulates over time, leading to mutations and dysfunction
- Telomere attrition: Protective caps on chromosomes shorten with each cell division, eventually limiting replication
- Epigenetic alterations: Chemical marks that regulate gene expression change with age, disrupting normal cell function
- Loss of proteostasis: The system that maintains proper protein folding and clears damaged proteins degrades
- Deregulated nutrient sensing: Metabolic pathways that respond to nutrients become dysregulated
- Mitochondrial dysfunction: Cellular energy production becomes less efficient
- Cellular senescence: Damaged cells that stop dividing accumulate and secrete harmful factors
- Stem cell exhaustion: The reservoir of cells that regenerate tissues depletes
- Altered intercellular communication: Signaling between cells becomes disrupted, including chronic inflammation
These processes interact. Mitochondrial dysfunction creates reactive oxygen species that damage DNA. DNA damage can trigger cellular senescence. Senescent cells release inflammatory factors that damage surrounding tissue. And so on.
Current Interventions
Lifestyle: The interventions with the strongest evidence for extending healthspan are lifestyle-based: regular exercise, not smoking, moderate alcohol, healthy diet, maintaining social connections, adequate sleep. These are not glamorous, but they work.
Caloric restriction: Reducing calorie intake (without malnutrition) extends lifespan in many organisms, from yeast to primates. Whether it extends human lifespan is uncertain; trials are impractical. But the metabolic pathways involved (like those regulated by sirtuins and mTOR) are targets for drug development.²
Metformin: This diabetes drug has shown associations with reduced mortality and disease in diabetic patients. The TAME (Targeting Aging with Metformin) trial is testing whether it provides benefits in healthy older adults.³
Rapamycin: This immune suppressant extends lifespan in multiple animal models. Its side effects limit human use, but related compounds (rapalogs) are being developed with better safety profiles.⁴
NAD+ precursors: Nicotinamide adenine dinucleotide (NAD+) declines with age. Supplementation with precursors (NMN, NR) is being tested to restore levels. Evidence in humans is limited.
Senolytics: Drugs that selectively kill senescent cells. In animal models, removing senescent cells improves function and extends healthspan. Human trials are underway for specific conditions (e.g., idiopathic pulmonary fibrosis).⁵
The honest assessment: Interventions exist that clearly improve healthspan (lifestyle), interventions that show promise in animals but are unproven in humans (rapamycin, senolytics), and interventions where the evidence is preliminary at best (most supplements and anti-aging treatments currently marketed). No intervention has been proven to substantially extend maximum human lifespan.
The Longevity Industry
Funding has exploded: Billions of dollars have flowed into longevity research and companies. Altos Labs launched with $3 billion in funding.⁶ Calico (Google/Alphabet), Unity Biotechnology, Juvenescence, and dozens of others are pursuing various approaches.
The approaches:
- Cellular reprogramming (reversing aspects of aging at the cellular level)
- Senolytics (clearing senescent cells)
- Metabolic modulation (targeting pathways like mTOR, sirtuins, AMPK)
- Blood factors (searching for young blood components that rejuvenate old tissues)
- Organ replacement and regeneration (replacing aged organs, as discussed in Chapter 5)
- AI-driven drug discovery for novel aging targets
The question: Is this investment premature enthusiasm for a problem science doesn't yet know how to solve? Or is it the beginning of a transformation as fundamental as the antibiotic revolution?
Notable Players
Research Institutions
Buck Institute for Research on Aging is dedicated to understanding aging biology.
National Institute on Aging (NIH) funds the majority of aging research in the United States.
Max Planck Institute for Biology of Ageing in Germany leads European research.
SENS Research Foundation promotes the "damage repair" approach to aging.
Major university labs at Harvard (David Sinclair, George Church), Stanford, MIT, and others drive foundational research.
Companies
Altos Labs is pursuing cellular reprogramming with unprecedented funding and scientific talent (including Shinya Yamanaka, who won the Nobel Prize for discovering reprogramming factors).
Calico (Alphabet/Google) takes a long-term research approach to understanding aging biology.
Unity Biotechnology is developing senolytic drugs, with candidates in clinical trials.
Life Biosciences invests in multiple longevity companies across different mechanisms.
BioAge Labs uses machine learning to identify aging biomarkers and drug targets.
Retro Biosciences is focusing on cellular reprogramming and organ transplant technologies.
Loyal is developing longevity drugs for dogs—both as a market and as a faster path to proving lifespan extension concepts.
Investors and Advocates
Wealthy individuals including Jeff Bezos, Peter Thiel, Larry Ellison, and Sam Altman have invested heavily in longevity research.
Aubrey de Grey (despite controversies) popularized the idea of treating aging as an engineering problem.
Laura Deming founded the Longevity Fund, focused on longevity investing.
Healthspan vs. Lifespan
A crucial distinction: living longer versus living better.
The Problem of Extended Frailty
If lifespan is extended without extending healthspan, the result is simply more years of disability, disease, and dependency. A cure for cancer that lets someone live to 95 instead of 85—but those extra years are spent with dementia in a nursing home—is not obviously a success.
The goal is not just more years but more good years: physical capability, cognitive function, independence, and quality of life.
The Compression of Morbidity
The optimistic scenario: morbidity (the period of disease and disability before death) gets compressed into a shorter period at the end of life. You're healthy and functional until 95, decline briefly, and die at 97.
The pessimistic scenario: morbidity expands. You develop chronic diseases at 65, spend 30 years in declining health, and die at 95. More life years, but most of them impaired.
Current trends are mixed. Life expectancy has increased, but evidence on whether the added years are healthy or disabled is contested and varies by population.⁷
Targeting Healthspan
The most promising longevity interventions target healthspan directly—not just preventing death but maintaining function:
- Senolytics aim to reduce inflammation and improve tissue function
- Exercise maintains muscle mass, cardiovascular health, and cognitive function
- Metabolic interventions aim to preserve cellular function
- Cognitive interventions aim to maintain brain health
The measure of success should be not just years lived but functional years—and the tools to measure and optimize healthspan are still developing.
Interventions on the Horizon
Cellular Reprogramming
The discovery: In 2006, Shinya Yamanaka showed that adult cells could be reprogrammed to a pluripotent state (like embryonic stem cells) by expressing four transcription factors (Oct4, Sox2, Klf4, c-Myc—the "Yamanaka factors").⁸
The insight for aging: If cells can be reset to a younger state, perhaps aging itself is reversible—not by making old cells into stem cells, but by partially resetting their age-related changes while keeping their identity.
Partial reprogramming: Expressing Yamanaka factors briefly can reverse some signs of cellular aging without fully dedifferentiating cells. In animal studies, this has improved tissue function and extended lifespan.⁹
Challenges:
- Too much reprogramming causes tumors (full dedifferentiation creates cancer-like cells)
- Delivery to the whole body is difficult
- The right "dose" of reprogramming is unclear
- Long-term effects are unknown
The Altos Labs bet: With $3 billion and top scientists, Altos is pursuing reprogramming-based rejuvenation. If they succeed, the implications would be transformative. But success is not guaranteed.
Trajectory: Plausible for demonstrating meaningful rejuvenation effects in animals and potentially humans. Wild for full reversal of biological age in humans within a decade.
Senolytics at Scale
The case for senolytics: Senescent cells accumulate with age, don't divide, and secrete inflammatory factors that damage surrounding tissue. Removing them improves function in animal models.
Current drugs: Dasatinib + quercetin (D+Q), fisetin, and other combinations have shown senolytic activity. Unity Biotechnology's UBX1325 targets senescent cells in the eye for age-related macular degeneration.
Challenges:
- Identifying which senescent cells to target (some may be beneficial)
- Delivering drugs to specific tissues
- Understanding long-term effects of repeated senolytic treatment
- Demonstrating human efficacy
Trajectory: Near-term likely for approval of senolytics for specific diseases. Plausible for broader use as longevity interventions. Whether senolytics alone can dramatically extend lifespan is unknown.
Young Blood Factors
The observation: When old and young mice share a circulatory system (parabiosis), old mice show improved function—rejuvenation of multiple tissues.¹⁰
The implication: Something in young blood helps old tissues; something in old blood harms young tissues.
The search: Researchers are identifying specific factors: GDF11, oxytocin, and others have been proposed as rejuvenation factors. Conversely, "pro-aging factors" might be targeted for removal.
Clinical attempts: Ambrosia and other companies offered young blood transfusions to paying customers. The FDA issued warnings; the evidence for benefit was minimal.¹¹
Serious research: Academic labs and companies are pursuing specific factors rather than whole blood, which is more likely to work and less likely to cause harm.
Trajectory: Plausible that specific factors are identified and tested. Wild for "young blood" as a practical rejuvenation therapy.
AI-Accelerated Drug Discovery
The opportunity: Aging involves many targets. Traditional drug discovery explores them slowly. AI could accelerate dramatically.
Current applications:
- Identifying aging biomarkers through machine learning on large datasets
- Predicting which compounds might have senolytic or other anti-aging properties
- Simulating cellular aging processes to identify intervention points
- Designing molecules targeting novel aging mechanisms
Examples: BioAge Labs uses ML on large datasets to identify aging biomarkers. Insilico Medicine has applied its AI platform to aging targets. Various academic groups use AI for aging research.
The hope: AI dramatically compresses the timeline from target identification to clinical candidate. What would take decades of incremental research happens in years.
Trajectory: Near-term likely for AI accelerating longevity research. Whether this is enough to produce breakthroughs is uncertain.
Scenarios: How Long Might Humans Live?
Conservative Scenario: Incremental Extension
Healthspan extends modestly through better lifestyle adoption, disease prevention, and targeted treatments. Life expectancy at birth in developed countries rises from ~80 to ~90 over 30 years. Maximum lifespan changes little.
What this looks like:
- More people remain healthy into their 80s
- Deaths from heart disease and cancer decline
- Dementia remains a major challenge
- The fundamental biology of aging is not reversed
- Death from "old age" remains normal in the 90s
Probability: This is the most likely scenario based on historical trends. Progress continues but is not transformative.
Moderate Scenario: Meaningful Healthspan Extension
Effective interventions (senolytics, metabolic drugs, perhaps partial reprogramming) add 10-20 years of healthy life for those who access them. Maximum lifespan rises to 120-130.
What this looks like:
- A 70-year-old has the functional capacity of today's 50-year-old
- Retirement age shifts upward
- Multi-generational workplaces become normal
- Social institutions adapt to longer lives
- Inequality between those with access and without becomes stark
Probability: Plausible. Several interventions show promise. Whether they combine to produce this outcome is uncertain.
Optimistic Scenario: Longevity Escape Velocity
Aging becomes a solved engineering problem. Interventions arrive faster than aging progresses—each year of life gains more than a year of healthspan. Practical biological immortality for those who access treatment.
What this looks like:
- Death from aging becomes optional rather than inevitable
- Population dynamics transform
- Retirement as a concept may disappear
- Wealth and power could concentrate in the indefinitely living
- Social structures built around generational turnover must adapt or collapse
Probability: Wild speculation. No current evidence suggests humanity is close to this. But the possibility cannot be dismissed entirely.
Second-Order Effects: The World of Long Lives
If lifespan and healthspan extend dramatically, nearly everything changes.
Retirement and Pensions
Current retirement systems assume people work for ~40 years and receive support for ~15-20. If people live to 120 in good health, this math collapses.
Possible responses:
- Retirement age rises (working until 80, 90, or later)
- Multiple careers become normal (nobody works the same job for 60 years)
- Pension systems restructure fundamentally
- Personal savings must last much longer
- "Retirement" as a concept changes or disappears
Family Structure
Current family structures assume grandparents die within the lives of their grandchildren. With radical longevity:
- Four, five, or more living generations become normal
- Inheritance patterns change (waiting until your parents die at 130 means inheriting at 100)
- Marriage and long-term relationships face new pressures ('"til death do us part" means something different at 50 years vs. 150)
- Parenting might happen at any age
- Family resources spread across more generations
Political and Economic Power
Power currently turns over partially through generational change. Old leaders die; new leaders emerge. With radical longevity:
- Power could entrench—the same individuals stay in positions for centuries
- Wealth accumulates indefinitely rather than redistributing at death
- Political change slows as generational turnover diminishes
- New ideas might face more resistance from those with entrenched positions
- Or: experienced leaders might govern more wisely with longer time horizons
Population and Resources
If death rates drop dramatically while birth rates remain constant, population grows. With current birth rates, this could be sustainable for a while—but eventually presses against resource limits.
Possible responses:
- Birth rates decline as people have children later or fewer
- Resource efficiency improves (through technology)
- Space colonization expands available resources
- Or: population pressure creates conflict and suffering
The optimistic view: With longer time horizons, people invest more in the future. Environmental protection, infrastructure, and sustainable development become more appealing when you'll live to see the consequences.
The pessimistic view: Entrenched interests resist change even longer. The old consume resources the young need. Generational conflict intensifies.
Meaning and Purpose
Current life structures assume finite time. You're young, then adult, then old, then dead. This arc provides meaning—urgency, legacy, the passing of torches.
With radical longevity:
- The urgency of a limited life diminishes
- Legacy matters differently when you're still around
- Boredom, purposelessness, and psychological challenges may increase
- Or: freed from the rush toward death, people pursue meaning differently
No one knows how humans would adapt psychologically to indefinite life. There is no experience with it. It might be wonderful. It might be hellish. It might be both.
Risks and Guardrails
Inequality
If longevity treatments are expensive and limited, the rich live while the poor die. This is morally unacceptable to many and practically dangerous.
Mitigation approaches:
- Public investment to drive down costs
- Universal access as a political commitment
- Regulation to prevent extraction pricing
- International coordination to prevent longevity tourism creating inequality
Entrenchment and Stagnation
If the same people hold power indefinitely, societies might ossify. Innovation, cultural change, and political evolution often come from generational turnover.
Mitigation approaches:
- Term limits become more important
- Mandatory career breaks or sabbaticals
- Institutions designed to inject new perspectives
- Cultural norms that value stepping aside
Population Pressure
More people living longer means more people—unless birth rates decline proportionally. And they might not decline fast enough.
Mitigation approaches:
- Voluntary birth rate reduction through education and opportunity
- Resource efficiency through technology
- Space expansion (very long-term)
- Difficult conversations about population policy
The Risk of Failure
Pursuing longevity might fail—not just failing to extend life, but causing harm: cancer from reprogramming gone wrong, infections from immune suppression, unexpected effects from systemic interventions.
The precautionary approach: Extensive testing, rigorous trials, and caution before deploying interventions broadly.
The urgency approach: 100,000 people die every day from aging-related causes. Excessive caution has its own body count.
Balancing these is not straightforward.
The Path Forward
Near-term likely (5-7 years):
- Senolytics approved for specific age-related diseases
- Better understanding of aging biomarkers enabling intervention tracking
- Lifestyle interventions promoted with renewed emphasis
- AI accelerating identification of aging targets and drug candidates
- Continued investment and research without definitive breakthroughs
Plausible (7-15 years):
- Interventions demonstrably extending healthy lifespan by 5-10 years
- Partial reprogramming approaches entering human trials
- Combination therapies addressing multiple hallmarks of aging
- Social and economic structures beginning to adapt to longer lives
- Significant inequality in access becoming politically salient
Wild (speculative):
- Aging effectively "solved"—biological age reversal possible
- Indefinite healthspan for those with access
- Radical restructuring of society around very long lives
- The meaning of human existence fundamentally altered
The dream of extending life is ancient. The technology to make it reality may be arriving. But neither technical success nor social adaptation is guaranteed.
What is certain is that the effort is serious, the funding is substantial, and the next decades will reveal whether humanity can truly escape its oldest fate.
Endnotes — Chapter 8
- López-Otín et al., "The Hallmarks of Aging," Cell (2013) and updated "Hallmarks of aging: An expanding universe," Cell (2023) provide the foundational framework for understanding aging biology.
- Caloric restriction effects have been demonstrated in organisms from yeast to primates. The CALERIE trials tested moderate caloric restriction in humans with mixed results on aging biomarkers.
- The TAME (Targeting Aging with Metformin) trial, led by Nir Barzilai, aims to test whether metformin delays age-related diseases in healthy older adults.
- Rapamycin extends lifespan in multiple model organisms. Side effects (immunosuppression, metabolic effects) limit human use. Rapalogs with better safety profiles are in development.
- Unity Biotechnology has conducted trials of senolytic candidates for age-related macular degeneration and other conditions. Results have been mixed.
- Altos Labs launched in 2022 with over $3 billion in funding, including investments from Jeff Bezos, to pursue cellular reprogramming approaches to rejuvenation.
- Evidence on compression of morbidity is contested. Some studies show healthy life expectancy rising with life expectancy; others show disability years expanding.
- Yamanaka's 2006 Cell paper demonstrated reprogramming of adult cells to pluripotent state using four factors, for which he shared the 2012 Nobel Prize.
- Studies from multiple labs have shown that partial reprogramming (brief exposure to Yamanaka factors or subsets) can reverse some signs of aging in cells and animal models without full dedifferentiation.
- Parabiosis experiments connecting old and young mice were pioneered by Clive McCay in the 1950s and revived by Tom Rando, Amy Wagers, and others in the 2000s-2010s.
- Ambrosia offered young plasma infusions to paying customers starting in 2017. The FDA issued a warning in 2019 that there was no proven clinical benefit and potential risks.