Why We Get Old & How We Can Stop It - Dr Andrew Steele - #265

Why '35-Year-Old Cavemen' Is a Statistical Illusion

Life expectancy figures like '35 years old for hunter-gatherers' or '40 in 18th-century UK' are heavily skewed by staggering infant and childhood mortality, not because adults dropped dead at 35. Steele notes hunter-gatherer children had roughly a coin-flip's chance of making it to adulthood.

• Average life expectancy ~20-30,000 years ago was around 35, and only 40 in the UK 200 years ago
• These averages are distorted by massive infant mortality, not short adult lifespans
• Roughly 60% chance of surviving to age 18-20 in deep prehistory
• Framed as 'basically tossing a coin to see if you'll make your 21st'

'Survival of the Fittest' Is the Wrong Phrase — It's Reproduction of the Fittest

Steele explains that aging exists because evolution optimizes for reproduction, not longevity or strength. An organism that spends energy on immortality (immune surveillance, cellular maintenance) has less energy for reproduction, so short-lived organisms that reproduce more can out-compete longer-lived ones evolutionarily.

• Popular phrase 'survival of the fittest' is misleading — it should be 'reproduction of the fittest'
• Surviving without reproducing means your traits vanish from the gene pool regardless
• Building an immortal body costs energy (cancer surveillance, maintenance) that could instead go to more offspring
• Longevity is just one of many traits evolution trades off against — sometimes the short-lived organism wins

No, Your Cells Don't All Replace Themselves Every 7 Years

Steele debunks the popular claim (often seen on social media) that every cell in your body is replaced every 7 years. Turnover rate varies wildly by tissue: gut cells turn over in days, red blood cells in months, but many neurons and heart cells are with you for life, protected by things like the blood-brain barrier.

• Gut lining cells turn over every few days; red blood cells last 3-4 months; bones roughly 7-10 years
• Some neurons and heart cells are never replaced — you're born and die with the same ones
• The blood-brain barrier keeps the brain's environment safe enough that most neurons don't need replacing
• Exception: olfactory (smell) neurons are exposed to the outside world and do turn over rapidly

Why Mouse Fasting Studies Might Be Measuring the Wrong Thing

Steele reveals a major confound in decades of dietary-restriction mouse research: because mice are nocturnal and the PhD students feeding them are not, calorie-restricted mice actually devour all their food in one sitting and then fast for 23 hours — accidentally combining calorie restriction with intermittent fasting. Only recently have researchers started using automated feeders to separate the two variables properly.

• Mice fed once at end of a human workday eat all their ration immediately, then go ~23 hours without food
• This means most 'calorie restriction' mouse studies were unintentionally also testing intermittent fasting
• Automated pet feeders (available for decades) have only recently been used to properly separate DR from IF in experiments
• Highlights a surprisingly basic methodological gap in a heavily-studied area of biology

Why Curing Aging Could Be Easier Than Curing Cancer

Steele argues that chasing aging as a root cause could be simpler than fighting cancer, heart disease, stroke, and dementia separately, since all of these diseases are driven by the same underlying biological processes and rise with age in the same exponential pattern. The alternative — treating thousands of individual disease codes — is described as an approach 'doomed to failure.'

• Cancer, heart disease, stroke, and dementia are overwhelmingly diseases of old age, driven by shared biological processes
• The International Classification of Diseases lists ~11,000 conditions — a large fraction are effectively downstream of aging
• Modern medicine typically treats symptoms several steps removed from the root cause
• Even curing cancer would leave 'an old body' still primed for heart disease and dementia

Why AI, Not a Single Pill, Will Be the Real Cure for Aging

Steele argues a genuine cure for aging will be far more complex than fixing the known hallmarks — it will require AI systems capable of interpreting biological data (genomes, proteins, 40 trillion interacting cells) at a scale no human can process, citing DeepMind's protein-folding breakthrough as an early sign of what's coming.

• A true 'cure' for aging will be more complicated than addressing the known hallmarks individually
• AI may be needed to interpret the sheer volume of biological data humans can't parse manually
• DeepMind's AI protein-folding breakthrough is cited as evidence rapid progress is possible
• Even a 50-years-away timeline could still arrive in time for people alive today, especially with health gains compounding

The Best Anti-Aging 'Hack' Isn't Diet — It's Political Pressure

After admitting he couldn't find a definitive optimal diet despite exhaustive research, Steele argues the single most impactful thing an individual can do for their own longevity is campaign for more aging research funding — because progress in aging biology will outweigh any personal lifestyle tweak.

• Standard health advice (don't smoke, exercise, avoid obesity) works because it slows the aging process, not just disease-specific risk
• A pack-a-day smoker is effectively ~10 years biologically older than their chronological age
• Steele concluded aging will likely be cured before scientists ever pin down the 'optimal diet' given the sheer number of variables
• His top recommendation: contact political representatives and push for aging research funding, since that will matter more than diet optimization

Why Steele Would Rather Extend His Biology Than Upload His Mind

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What Aging Actually Means: Two Scientific Definitions

Andrew Steele gives two ways scientists define aging: a statistical definition (how your risk of death changes with time) and a biological definition (the hallmarks of aging — measurable molecular changes that drive disease). Human mortality risk doubles roughly every 8 years, while giant tortoises show almost no increase in death risk with age at all.

• Statistical definition: aging = how much your risk of death rises with time
• Human risk of death doubles every ~8 years (the 'mortality rate doubling time')
• At 30, annual death risk is ~1 in 1,000; at 80 it's ~5% — a 200x increase
• Giant tortoises are 'negligibly senescent' — their death risk barely changes with age
• Biological definition: the 2013 'Hallmarks of Aging' paper lists 9 molecular changes that accelerate or slow aging when manipulated

Why We Age: The Evolutionary Energy Trade-Off

Aging happens because bodies stop investing as much energy into self-maintenance as we get older, redirecting it toward reproduction instead. Steele explains this as an evolutionary compromise: an individual who has more kids earlier will out-number the descendants of one who lives slightly longer but reproduces less.

• Bodies decide, in evolutionary terms, not to keep investing maximal energy into maintenance as we age
• More kids now compounds across generations and outweighs a small individual lifespan advantage
• In a world where death by accident/predation/infection is common, the numbers game favors early reproduction over longevity
• This trade-off is why aging exists as a byproduct of evolution rather than a deliberate program

Senescent Cells: The 'Zombie Cells' Behind Aging — and Drugs That Kill Them

Steele explains the discovery of senescent ('zombie') cells by Leonard Hayflick in the 1960s, and the landmark 2011 Mayo Clinic experiment where genetically modified mice could selectively kill their own senescent cells with a drug. The result: mice lived longer, got cancer and cataracts later, and behaved more like young mice — one of the most promising fronts in anti-aging research.

• Senescent cells were first identified by Leonard Hayflick in the 1960s — cells that stop dividing after ~50 divisions and look visibly abnormal
• In 2011, Mayo Clinic scientists engineered mice with a 'suicide switch' gene that killed only senescent cells when triggered by a drug
• Senolytic treatment made mice healthier, live longer, get cancer/cataracts later, and behave more curious/youthful in maze tests
• Senolytics are imperfect — they don't kill all senescent cells — yet still produced strong benefits in mice

Two Monkey Studies, Two Opposite Answers on Dietary Restriction

Steele unpacks why two major primate studies on calorie restriction reached different conclusions: the University of Wisconsin study (junk-food-style pellet diet for controls) showed longer lifespan from restriction, while the NIA study (more natural, varied diet) showed better health but no lifespan increase — suggesting restriction mainly helps when your baseline diet is already unhealthy.

• University of Wisconsin monkeys ate 'fast food'-style sugary/fatty pellets ad libitum as controls; restriction extended their lives
• NIA monkeys ate a more natural, varied diet; restriction improved health but did not extend lifespan
• Suggests dietary restriction may only help significantly if your baseline diet is already poor
• Both studies agreed restriction improves health even where it didn't extend lifespan
• Steele's overall bet: DR likely improves health but doesn't dramatically extend human lifespan

The Immortal Cheetah Thought Experiment: Why Death Might Help Evolution

Steele uses a hypothetical of immortal cheetahs on the savanna to explain why death may serve a purpose for evolution even if aging itself doesn't. Because evolution only happens between generations via new DNA combinations, a species that never died couldn't adapt if its environment changed — such as a sudden famine wiping out its food source.

• Evolution requires new gene combinations from reproduction — an individual's DNA is fixed for life
• Immortal cheetahs facing a prey collapse couldn't adapt their fixed traits (teeth, running speed, diet) fast enough
• Only through births across generations can a species gradually shift traits to survive environmental change
• It's an open scientific question how important this effect really is, but a literally immortal species could be evolutionarily doomed by a changing environment

The Greenland Shark, the 4,850-Year-Old Tree, and the Immortal-ish Hydra

Steele runs through nature's longevity extremes: a 400-year-old Greenland shark (the longest-lived vertebrate), a 4,850-year-old bristlecone pine in California that predates the pyramids, and Hydra — tiny freshwater creatures that can regenerate from a chopped-up fragment and may see 10% of a population still alive after 1,000 years.

• The Greenland shark is the longest-lived vertebrate, estimated at ~400 years old via chemical analysis
• A bristlecone pine in California's White Mountains is ~4,850 years old — its location is kept secret to prevent vandalism
• Hydra can be chopped into pieces and each piece regenerates into a new Hydra
• Extrapolated death rates suggest 10% of Hydra could still be alive after 1,000 years
• Tardigrades are noted as famously extreme survivors, though good longevity data on them doesn't exist

The 1930s Rat Study That Discovered Calorie Restriction Extends Life

Steele recounts the first formal aging experiment, run by Clive McCay in the 1930s, which found rats fed roughly half the calories of control rats lived about 80% longer — and looked just as healthy at death as rats that died far earlier. The effect has since been replicated across yeast, flies, mice, dogs, and more, but remains unproven in humans.

• Clive McCay's 1930s rat study cut caloric intake roughly in half while keeping nutrients adequate
• Calorie-restricted rats lived ~80% longer and appeared healthy, not frail, at time of death
• The effect has been replicated in yeast, flies, mice, dogs, and other species
• Human effectiveness remains unproven — monkey studies show healthier but not necessarily longer lives

A Real Gene-Therapy Breakthrough: Curing Sickle Cell Anemia

Steele shares a then-fresh news story about the first successful gene therapy trial for sickle cell anemia — extracting bone marrow stem cells, reactivating a dormant fetal hemoglobin gene, wiping out the old blood stem cells with chemotherapy, and reinserting the modified cells to restore normal blood function.

• Sickle cell anemia causes C-shaped blood cells that carry less oxygen and jam small blood vessels, causing severe pain
• The gene persists in African populations because one copy protects against malaria by disrupting mosquito feeding
• Scientists extracted bone marrow stem cells, reactivated the dormant fetal hemoglobin gene, and reinserted them after chemotherapy wiped out old stem cells
• Called one of the first real-world proofs of the cell/gene therapy techniques Steele covers in his book

He Started 16:8 Fasting — Then a Study Said It Does Nothing

Steele shares the irony of starting a 16:8 intermittent fasting regimen with his wife, only for a randomized controlled trial to be published that same week showing no measurable difference in weight, inflammatory markers, or cholesterol between 16:8 dieters and controls — leading the study's own author to abandon the practice immediately.

• Steele and his wife began 16:8 time-restricted eating (skip breakfast, eat between 12pm-8pm)
• A randomized trial (in slightly overweight white participants) found no difference in weight, inflammation, or cholesterol vs controls
• The study's lead scientist reportedly said he was convinced by 16:8 fasting until the trial, and stopped practicing it immediately after
• Illustrates how quickly promising lifestyle interventions can be undercut by rigorous trial data

The Bizarre 1920s Fad of Monkey Testicle Transplants

A lighthearted historical aside: in the 1920s there was a genuine trend of people attempting monkey testicle transplants in pursuit of rejuvenation and longevity, a claim both hosts find baffling and can't fully explain the logic behind.

• In the 1920s there was a documented movement around monkey testicle transplants for anti-aging purposes
• Neither host could clearly explain the scientific rationale behind the practice
• Framed as an example of how far anti-aging quackery has come from historical fads to modern cell/gene therapy

NMN, Resveratrol, Metformin: Are Any Longevity Supplements Worth Taking?

Asked directly about NMN, NAD, resveratrol, metformin, baby aspirin and the 'David Sinclair stack,' Steele says he personally takes none of them due to insufficient human trial evidence, but flags metformin — an existing diabetes drug — as the most promising near-term candidate given a major trial underway and suggestive data that diabetics on it may outlive non-diabetics.

• Steele personally takes none of the popular longevity supplements (NMN, NAD, resveratrol, etc.) due to lack of human trial evidence
• He's more excited by epigenetic reprogramming (which fixes underlying biology) than by supplements
• Metformin, an existing diabetes drug, has suggestive evidence that diabetics taking it can outlive non-diabetics despite worse baseline health
• A major US metformin-aging trial in healthy 60-somethings was underway (delayed by COVID) with results expected within ~5 years
• His advice: young people can afford to wait for trial data; older people face more of a Pascal's-wager calculus

Would Living to 200 Actually Change How We Live Day to Day?

Asked whether dramatically extending lifespan (80 to 160-200 years) would change how we find meaning in life, Steele argues it probably wouldn't change much personally, since most people already don't plan or live with their eventual death as a driving motivator — but he does think it could make society far more risk-averse about accidents and warfare.

• Steele argues people rarely act day-to-day based on awareness of eventual death as a motivator
• He predicts he'd still live 'day-to-day and week-to-week' even with a 160+ year lifespan
• Longer lifespans could make society much more risk-averse about accidents, since more life-years are at stake
• Could also make war culturally less acceptable, since the 'cost' in lost future life years would be far higher

Strength Training: The Most Underrated Anti-Aging Intervention

Steele highlights strength training as an area he personally neglected, noting muscle mass and strength decline slowly from the mid-30s and then fall off a cliff in the 60s and 70s — but this decline is largely optional. A study on nonagenarians given strength training showed improved walking speed and lifting capacity, proving it's never too late to start.

• Muscle mass/strength decline starts in the mid-30s and accelerates sharply in the 60s-70s
• This decline is largely optional — resistance training can ward off frailty at any age
• A study gave strength training to people in their 90s (nonagenarians), improving walking speed and lifting strength
• Take-away: it's never too late to start strength training for quality of life