The reference library
Forty-five body systems, and what each one is missing
The research the book was built from, as in-depth reference topics. Each takes one system, states what it evolved to expect, what the modern environment supplies instead, and what the gap does, with its mismatch card, its graded recommendations and the case against it. Each entry links to the chapter of the book that covers it.
- Reference essay
The Staircase
In 1966, five healthy young men in Dallas spent three weeks in bed. When they got up, they had lost more aerobic fitness than the next three decades of aging would take from them.
- Reference essay
The View from Here
Climbing is the easy part. This book pictures human history as a spiral staircase that turns at fire, agriculture, industry and the digital world.
The Ground Floor
- Topic 1Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The 200-Million-Year Warm-Up
How mammal evolution still shapes the human body
- Expects.
- High energy costs paid for by effortful foraging; real darkness at night; changing temperatures; food judged by color and smell.
- Gets.
- Abundant calories, climate-controlled rooms, bright evenings, engineered food colors.
0 graded recommendations · 68 sources · In the book: Chapter 2
- Topic 2Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
Standing Up
Why humans became bipedal, and what standing up costs
- Expects.
- Kilometers of walking most days, some running, carrying and throwing, and warm air that sweat can cool.
- Gets.
- Chairs, cars and desks; nearly a third of adults worldwide below minimum activity.
4 graded recommendations · 69 sources · In the book: Chapter 3
- Topic 3Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Expensive Organ
Why human brains got so big, and what they need
- Expects.
- Cooked, varied food; sleep; a band of about 30 people inside a wider network; daily physical and mental challenge.
- Gets.
- Long hours seated (Chapter 6), isolation for some, and prices, deadlines and risks its defaults never met.
7 graded recommendations · 79 sources · In the book: Chapter 5
- Topic 4Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Last Ice Age and the Birth of Agriculture
Agriculture and human health: what farming did to the body
- Expects.
- A varied diet of wild plants and animals, daily walking and carrying, small mobile groups, seasonal variety.
- Gets.
- Cereals supplying 42% of the world's dietary energy, sedentary work, and dense settlements shared with animals and strangers.
0 graded recommendations · 83 sources · In the book: Chapter 2
- Topic 5
The Idea of Mismatch
Who proposed evolutionary mismatch? The idea and its history
0 graded recommendations · 42 sources · In the book: Chapter 2
The Body that Moves
- Topic 6Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Sitting Disease
Sitting too much: the health effects, and what actually helps
- Expects.
- Hours of walking and carrying, and rest in postures (squatting, kneeling, ground-sitting) that keep leg muscles working.
- Gets.
- About 7.7 sedentary hours a day for the average American, and too little activity for nearly a third of adults worldwide.
7 graded recommendations · 58 sources · In the book: Chapter 3
- Topic 7Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Foot That Forgot the Ground
Barefoot shoes and foot strength: what the evidence says
- Expects.
- Bare or thinly shod feet on varied ground, working the arch and toes daily.
- Gets.
- Cushioned, arch-supported, toe-sprung shoes on flat floors from early childhood.
5 graded recommendations · 50 sources · In the book: Chapter 3
- Topic 8Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Heart That Remembers the Savanna
Heart disease and evolution: why the heart needs movement
- Expects.
- Hours of light and moderate activity daily, little salt, plenty of potassium, a lean body and low LDL for life.
- Gets.
- Long sitting, about 11 g of salt a day on the global average, too little potassium, abundant food.
8 graded recommendations · 64 sources · In the book: Chapter 3
- Topic 9Evidence grade: Emerging. Early, small, animal-only, or actively contested.
The Invisible River
The lymphatic system: how it works, and what keeps lymph moving
- Expects.
- Kilometers of walking a day, shifting postures, regular nights of sleep.
- Gets.
- Unbroken sitting, long-haul seats, short nights and, for some, severe obesity.
6 graded recommendations · 55 sources · In the book: Chapter 3
- Topic 10Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Breath You Forgot How to Take
Nose breathing vs mouth breathing: what the evidence says
- Expects.
- An open nose at rest and in sleep, with the mouth joining in for hard effort.
- Gets.
- Noses often blocked by allergy, which pushes breathing to the mouth, and breathing hacks that outpace their trials.
6 graded recommendations · 49 sources · In the book: Chapter 13
The Body that Eats
- Topic 11Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Hijacked Reward System
Why we crave sugar: dopamine, reward and modern food
- Expects.
- Sugar that costs effort or comes wrapped in fruit, ethanol at a fraction of a percent, and food that takes time to chew.
- Gets.
- Ultra-processed food supplying 55% of American calories, and alcohol in concentrated drinks.
5 graded recommendations · 67 sources · In the book: Chapter 5
- Topic 12Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Gut That Expects Dirt
Gut microbiome health: fiber, dirt and what the evidence says
- Expects.
- Tens of grams of fiber a day from many plants, a seasonal menu, and microbes from soil and food.
- Gets.
- About 17 g of fiber a day (the US adult average), a narrow and refined diet, courses of antibiotics, and sanitized surroundings.
7 graded recommendations · 74 sources · In the book: Chapter 6
- Topic 13Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Thrifty Body
Appetite, fat storage and obesity: the thrifty body
- Expects.
- Food that takes work to get, lean seasons, fiber-rich plants and hours of physical work.
- Gets.
- Cheap, energy-dense, ultra-processed food all day, little physical work and short sleep.
7 graded recommendations · 89 sources · In the book: Chapter 5
- Topic 14Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Liver and the Chemical Century
Liver detox: what the liver actually does with modern chemicals
- Expects.
- Daily plant defense chemicals, occasional natural toxins such as aflatoxin, and food energy that took work to get.
- Gets.
- Surplus calories from sugary drinks and alcohol, and more than 350,000 registered chemicals and mixtures, a few of them, such as the long-lived PFAS, beyond its power to break down.
9 graded recommendations · 72 sources · In the book: Chapter 5
- Topic 15Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Tongue and the Nose
Loss of smell and taste: the chemical senses in a modern world
- Expects.
- Sugar wrapped in fiber, bitter and sour plants, and a nose used daily to find food and judge freshness.
- Gets.
- Sugar dissolved in drinks at all hours, debittered crops, sweeteners, polluted air, smoke, viruses and an underused nose.
6 graded recommendations · 62 sources · In the book: Chapter 5
- Topic 16Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Shrinking Face
Why are human jaws getting smaller? Crowded teeth explained
- Expects.
- Hard chewing from childhood, teeth that wear flat, a clear nose, little free sugar.
- Gets.
- Soft processed food, fork-cut mouthfuls, industrial flour and sugar, and more body weight pressing on the airway.
7 graded recommendations · 66 sources · In the book: Chapter 8
- Topic 17Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Water You Forgot to Drink
How much water should you drink a day? What thirst evolved for
- Expects.
- Wet food and drinking to thirst, in an ape that turns over 30% to 50% less water than its cousins, size for size.
- Gets.
- Taps, climate control, a 1945 allowance stripped of its caveats, and a market selling hydration.
8 graded recommendations · 42 sources · In the book: Chapter 5
The Body that Defends
- Topic 18Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Immune System's Education
The hygiene hypothesis: allergies, asthma and the immune system
- Expects.
- Early years full of microbes from siblings, animals, soil, water and food, and early tastes of lifelong foods.
- Gets.
- Small families, indoor lives, fewer animals and, until recently, advice to delay allergenic foods.
5 graded recommendations · 69 sources · In the book: Chapter 6
- Topic 19Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Largest Organ
Vitamin D from sun vs supplements, and what skin evolved for
- Expects.
- Sun matched to its pigment, changing gradually with the seasons, mostly outdoors and often in shade.
- Gets.
- Pale skin under subtropical sun, dark skin at high latitudes, indoor lives and sudden, burning doses.
7 graded recommendations · 79 sources · In the book: Chapter 7
- Topic 20Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Fever and the Old Enemies
Should you let a fever run its course? What fever is for
- Expects.
- Infection as the commonest threat, care from others while sick, and bands too small for crowd diseases.
- Gets.
- Crowd and herd diseases, fever treated as the enemy, work while sick, antibiotics overused and vaccines refused.
6 graded recommendations · 75 sources · In the book: Chapter 6
- Topic 21Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Pain You Were Not Supposed to Keep
Chronic pain and back pain: why pain persists
- Expects.
- Injury, then a return to use while still sore, among people who help.
- Gets.
- Rest, scans that find "damage" in pain-free people, fear and, for a time, freely prescribed opioids.
7 graded recommendations · 62 sources · In the book: Chapter 3
- Topic 22Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
Cancer in a New Environment
Why is cancer increasing in young adults? The evidence
- Expects.
- A body of ancestral size and lifespan; menarche in the mid-teens, many pregnancies, years of breastfeeding; no tobacco and little alcohol.
- Gets.
- Longer lives; earlier menarche, fewer and later births and shorter breastfeeding (three to four times the Dogon's menstrual cycles); excess body fat; tobacco and alcohol.
10 graded recommendations · 60 sources · In the book: Chapter 16
The Body that Reads Signals
- Topic 23Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
Sleep and the Dark You Have Lost
Light at night and sleep: blue light, darkness, body clock
- Expects.
- A bright day, a dark night, a falling evening temperature, and the same schedule tomorrow.
- Gets.
- Days under 100 lux indoors, evenings at 30 to 300 lux, a lit bedroom, a schedule that moves at weekends.
5 graded recommendations · 80 sources · In the book: Chapter 8
- Topic 24Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Indoor Eye
Myopia in children: causes, screen time and time outdoors
- Expects.
- A childhood of bright outdoor light, thousands of lux for hours a day, with things to look at near and far.
- Gets.
- Years of classrooms at a few hundred lux, and 87% of time spent inside a building.
5 graded recommendations · 57 sources · In the book: Chapter 7
- Topic 25Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Thermoneutral Trap
Cold exposure benefits and brown fat: what the evidence says
- Expects.
- A day and a year that leave the thermoneutral band: cold mornings, hot afternoons, cooling nights.
- Gets.
- 18°C to 25°C indoors, all year, for about 87% of the time.
4 graded recommendations · 62 sources · In the book: Chapter 9
- Topic 26Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Ear in the Silent Room
Noise exposure and hearing loss: the ear in a loud world
- Expects.
- Intermittent loud events against a quiet, information-rich natural background, plus music made in groups.
- Gets.
- Continuous mechanical noise, including at night, and music delivered privately through earbuds.
6 graded recommendations · 16 sources · In the book: Chapter 10
- Topic 27Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Green Prescription
Nature and mental health: what green space does to stress
- Expects.
- Daylight hours among plants, water and animals, with shade and people nearby.
- Gets.
- Most of life spent indoors, a view of a wall, and a city hotter and louder than the land it replaced.
8 graded recommendations · 44 sources · In the book: Chapter 10
The Social Animal
- Topic 28Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
Stress and the Hijacked Alarm
Chronic stress: cortisol, and why the alarm stays on
- Expects.
- Threats that arrive, get answered with the body, and end, among allies.
- Gets.
- Uncontrollable social evaluation without end, in steep hierarchies, carried into the night on short sleep and thin company.
7 graded recommendations · 67 sources · In the book: Chapter 13
- Topic 29Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Social Animal in Solitary Confinement
Loneliness and health: why social isolation harms the body
- Expects.
- Daily, face-to-face, reciprocal contact with a small stable band, inside a wider network of roughly 150 known people.
- Gets.
- Fewer confidants than a generation ago, most waking contact mediated by screens, and a follower count standing in for a circle.
4 graded recommendations · 16 sources · In the book: Chapter 11
- Topic 30Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Attention Economy and the Boredom Deficit
Phones, boredom and attention: what screens do to the brain
- Expects.
- Rewards that are earned, spaced and occasionally absent, separated by long intervals with nothing to attend to.
- Gets.
- A pocket device engineered for time on device, paying out on a variable schedule and filling every gap in the day.
4 graded recommendations · 14 sources · In the book: Chapter 12
- Topic 31Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Mind That Cannot Find Its Village
Why is anxiety on the rise? An evolutionary view of mood
- Expects.
- Threats that are physical, local and resolvable; problems a small group can help solve; a world where scanning and moving pay.
- Gets.
- Unresolvable threats delivered continuously, thin social support, and settings that reward long stillness and narrow focus.
5 graded recommendations · 17 sources · In the book: Chapter 13
The Life Course
- Topic 32Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Reproductive Paradox
Declining sperm counts and fertility: the reproductive mismatch
- Expects.
- Steady energy availability, first births while fertility is at its peak, kin nearby to subsidize weaned children, and a lifetime of relatively few ovulatory cycles (Chapter 22).
- Gets.
- Energy surplus or deficit rather than balance, a mean first birth at 27.5 in the United States, grandparents in other cities, and an industrial chemical environment nobody has fully characterized.
5 graded recommendations · 19 sources · In the book: Chapter 15
- Topic 33Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
Born Too Soon
Human birth and evolution: why babies are born so helpless
- Expects.
- A labor attended continuously, several pairs of hands afterwards, a founding microbial community from the birth canal, milk carrying sugars for the infant's bacteria, and sleep within reach of an adult.
- Gets.
- More than one birth in five by cesarean, staff who rotate, formula without the same sugars, a mother recovering largely alone, and in many homes an infant asleep behind a closed door.
4 graded recommendations · 11 sources · In the book: Chapter 11
- Topic 34Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Children's Mismatch
Children's health and outdoor play: the childhood mismatch
- Expects.
- Most of the daylight hours in unsupervised, mixed-age, child-directed play, outdoors, with graded doses of real risk.
- Gets.
- Adult-scheduled, age-segregated, refereed activity indoors, with risk engineered out and a screen in the gaps.
6 graded recommendations · 11 sources · In the book: Chapter 12
- Topic 35Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Hallmarks of Aging
The hallmarks of aging: all twelve, explained
- Expects.
- Muscles loaded most days, food that comes and goes, microbes, and stressors that end.
- Gets.
- Decades of low mechanical load, continuous food, and stress without resolution.
6 graded recommendations · 15 sources · In the book: Chapter 16
- Topic 36Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.
Why We Die the Way We Do
Leading causes of death, and how long people are ill first
- Expects.
- A body that moves, eats, defends, senses and socializes in the conditions of Parts Two to Seven, with death arriving mostly from outside (infection, accident, violence) after a modal age in the seventies.
- Gets.
- Those conditions removed one at a time, with medical treatment supplied for each resulting failure.
0 graded recommendations · 12 sources · In the book: Chapter 16
Finding the Handrail
- Topic 37Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.
The Individual Variable
Lactose intolerance and evolution: genes tuned to diet and place
- Expects.
- The diet, altitude, sunlight and pathogens of the place where your recent ancestors lived and reproduced.
- Gets.
- Global food supply, air travel, latitude changes within a single lifetime, and a consumer test that reports ancestry as if it reported physiology.
4 graded recommendations · 21 sources · In the book: Chapter 2
- Topic 38
The Case Against This Book
The case against evolutionary mismatch: critics and evidence
0 graded recommendations · 18 sources · In the book: Chapter 2
- Topic 39Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Unified Field of Mismatch
Chronic inflammation: the thread linking modern disease
- Expects.
- Inflammation as an emergency, switched on for an infection or a wound and switched off after.
- Gets.
- A standing low-grade version of the same signal, fed by inactivity, poor diet, disrupted sleep, chronic stress, pollutants and infection.
0 graded recommendations · 8 sources
- Topic 40Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Handrail I: Move, Eat, Drink
How to move, eat and drink for the body you evolved
- Expects.
- Several hours a day of unremarkable movement, occasional hard bursts, loads carried, food that spoils, and water when thirsty.
- Gets.
- About 5,100 steps, chairs, engines, food engineered to be eaten quickly, and a hydration industry.
11 graded recommendations · 22 sources · In the book: Chapter 1
- Topic 41Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Handrail II: Light, Sleep, Temperature, Nature
Light, sleep, temperature and nature: graded daily habits
- Expects.
- Thousands of lux by day, near-total darkness at night, a temperature that falls after sunset, occasional cold and heat, and daily hours outdoors.
- Gets.
- Under 1,000 lux of waking light in the week the campers spent at home, evenings in the 30 to 300 lux band the clock reads most steeply, a thermostat that never moves, and most of a life indoors.
9 graded recommendations · 25 sources · In the book: Chapter 1
- Topic 42Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Handrail III: People, Attention, Meaning
Connection, attention and purpose: advice for the social brain
- Expects.
- Daily presence among a small, stable group; touch as a routine event; effort before reward; a role the group depends on.
- Gets.
- A wide, thin network delivered through glass, touch made optional, reward decoupled from effort, and purpose left to arrange itself.
8 graded recommendations · 14 sources · In the book: Chapter 1
- Topic 43Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
The Mismatch Within the Mismatch
How to form habits that stick, and why willpower fails
- Expects.
- An environment that supplies the right behavior by default, so that eating, moving, sleeping and resting require no deliberation.
- Gets.
- An environment that supplies none of them, plus a $6.8 trillion market selling deliberation back as the remedy.
5 graded recommendations · 9 sources · In the book: Chapter 1
The Next Turn
- Topic 44Evidence grade: Emerging. Early, small, animal-only, or actively contested.
The Luxury Trap Accelerates
Cognitive offloading: what GPS, search and AI do to memory
- Expects.
- Daily problems that must be solved with the equipment inside the skull, in a world where nobody else holds the answer.
- Gets.
- An external store for every fact, a route for every journey and, lately, a competent draft of almost any piece of thinking, available before the effort starts.
5 graded recommendations · 14 sources · In the book: Chapter 12
- Topic 45Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.
Designing the Bridge
Designing healthier environments: changing the defaults
- Expects.
- A place whose ordinary defaults deliver load, daylight, darkness, heat, cold, microbes and company without anyone having to decide on them.
- Gets.
- Environments built around cars, screens, shelf life and margin, with the missing signals sold back as effort, subscription or supplement.
5 graded recommendations · 27 sources · In the book: Epilogue
- Topic
The View from Here
0 graded recommendations · 10 sources · In the book: Epilogue