The idea, and its limits
Evolutionary mismatch
The gap between the world a body evolved in and the world it lives in now. This page gives the definition, examples in humans, where the idea came from, the three tests a mismatch claim has to pass, and the places where the idea is routinely overclaimed.
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What is evolutionary mismatch?
Evolutionary mismatch is the gap between the world a body evolved in and the one it lives in now. Your body reads signals from its surroundings, movement, light and darkness, microbes, heat and cold, food, other people, and was built for the versions its ancestors knew. Modern life gives it too much of some, too little of others and much that is new. In that gap, researchers suspect, lie many chronic diseases (Topic 5).
The idea sits inside a larger question. Randolph Nesse and George Williams, the founders of what they called Darwinian medicine, concluded that diseases do not have evolutionary explanations. What has an evolutionary explanation is the vulnerability: the aspects of a body that leave it open to disease. Mismatch is one of six such explanations, and the one this book follows above all, because it is the kind an environment can change.
The book states the whole argument in five words: the environment is the intervention. In 1966, five healthy young men in Dallas spent three weeks in bed, and lost more aerobic fitness than the next three decades of aging would take from them. Nothing had been done to them. Something had been taken away.
Examples of evolutionary mismatch in humans
Six of the book's mismatch cards, in its own words. Each chapter states one.
Chapter 3: The Body That Walks
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.The walking body: leg muscles and joints, heart and blood vessels, lymph, back and feet.
- Expects
- Hours on foot most days, rest in squats and on the ground, little salt and plenty of potassium, and use of a sore body while it heals.
- Gets
- Nearly eight sedentary hours a day and about 5,100 steps for the average American, about 11 g of salt a day worldwide, and rest, scans and fear after injury.
Chapter 4: Load, Strength and Bone
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Skeletal muscle and bone, which calibrate their strength to the loads they carry.
- Expects
- Daily walking, carrying and lifting, often heavy, across a whole life.
- Gets
- Chairs, wheels and machines; little that is heavy; and, for women, a menopausal transition that speeds bone loss with no extra load to answer it.
Chapter 5: Eat
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.Appetite and fuel: the gut, liver, muscle and fat, and the reward circuits that steer eating.
- Expects
- Food that took work to get and time to chew, sugar wrapped in fiber, alcohol at a fraction of a percent, and water when thirsty.
- Gets
- More than half its calories from ultra-processed food, sugar and alcohol in concentrated drinks, and little physical work.
Chapter 6: The Gut That Expects Dirt
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.The gut's microbes and the immune system's learned tolerance.
- Expects
- Tens of grams of fiber a day from many plants; microbes from siblings, animals, soil and food; early tastes of lifelong foods; fever and care while sick.
- Gets
- About 17 g of fiber a day (the US adult average), small families and indoor lives, needless antibiotics, delayed allergenic foods until recently, and fear of the thermometer.
Chapter 7: Light and Dark
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.The circadian clock, set through melanopsin in the eye; skin pigment and vitamin D; the growing eye.
- Expects
- Bright days, truly dark nights, sun matched to skin and changing with the seasons, and a childhood spent largely outdoors.
- Gets
- Days mostly indoors under room light far dimmer than any sky, evenings lit brightly enough to hold the clock back, lit bedrooms, pale skin under sudden holiday sun and dark skin in indoor lives, and classrooms instead of fields.
Chapter 8: Sleep
ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.The circadian clock and the sleep it schedules, tuned by light, temperature and routine.
- Expects
- A bright day, a dark night that cools, and the same timing tomorrow; enough sleep, with room for naps.
- Gets
- Dim days, lit evenings, a bedroom at one temperature with a phone in it, a schedule that lurches at weekends, afternoon caffeine, and for some, work through the night.
What are mismatch diseases?
Many chronic diseases are suspected mismatches, graded chapter by chapter; local genetic tuning means the gap differs from person to person.
Book, Chapter 2: What Your Body Expects, and How to Trust This Book, mismatch card
The authors conclude that chronic low back pain is not a mismatch disease (one born of the gap between evolved bodies and modern lives) limited to post-industrial populations (Topic 21).
Lieberman's own table of about 50 conditions, from acne to flat feet, lists "suspected" mismatch diseases.
Dysevolution: Daniel Lieberman's term for the loop in which medicine treats the symptoms of mismatch diseases while the environments causing them are passed on.
Where the idea came from
- 1962, the question mark. The geneticist James Neel published Diabetes mellitus: a "thrifty" genotype rendered detrimental by "progress"? Genes that raise diabetes risk, he proposed, may once have been an advantage. The thrifty-gene hypothesis itself has fared badly (Topic 13). The thought behind it has not.
- 1985, the hypothesis. S. Boyd Eaton, a radiologist at Emory, and Melvin Konner, an anthropologist who had lived with the !Kung San of Botswana, published Paleolithic Nutrition, later called by its authors the first publication of the evolutionary discordance hypothesis.
- 1988, the word. With Marjorie Shostak, the pair published Stone Agers in the Fast Lane, which found the term for the whole idea: people today are "Stone Age hunter-gatherers displaced through time to a world that differs from that for which our genetic constitution was selected," and "the resulting mismatch fosters ‘diseases of civilization.’"
- The framework. Nesse and Williams turned the question around: not why a disease exists, but why selection left the body open to it. Daniel Lieberman later popularised mismatch for general readers.
The first edition of this book credited the idea to Lieberman alone. That attribution was wrong and is listed among the corrections.
The three tests
An idea this flexible can explain nearly anything, so the field has worked to make it testable. In 2023 a large team set out three conditions a mismatch claim should meet (Topic 5):
- 1
More common in the new world
The condition must be more common or severe in the new environment than in the old.
- 2
Tied to a specific factor
It must be tied to a specific environmental factor that differs between the two.
- 3
With a mechanism
There must be a mechanism, ideally a gene variant with a history of selection that helps in the old setting and harms in the new.
The same team added a caution that most popular writing ignores: today's subsistence peoples "are not themselves ‘ancestral’ populations." Knee osteoarthritis passes the first test cleanly. In skeletons of older Americans it was 2.1 times as common after industrialisation as before, adjusting for age and body mass, and prehistoric hunter-gatherers and early farmers had low rates too. Skeletons cannot say which modern factor did it, so tests two and three remain open (Topic 5).
Mismatch is one of six reasons a body stays vulnerable
Nesse lists six: "mismatch, coevolution, tradeoffs, constraints, reproductive advantage at the expense of the individual, and defenses that are aversive but useful." Treating every complaint as mismatch is the commonest way the idea gets misused (Topic 5).
- Mismatch
- Environments changed faster than genes could follow.
- Coevolution
- A race against pathogens that evolve far faster than we can.
- Constraints
- Selection can only modify what already exists, which is why the eye is wired inside out.
- Trade-offs
- Making one trait better makes another worse. Sickle-cell trait guards against malaria at a cost.
- Reproduction, not health
- Selection maximises reproduction. A gene that helps early can spread even if it harms decades later.
- Useful defences
- Fever, pain, cough and anxiety feel like illness but can protect you, and are tuned to raise false alarms.
The four turns of the staircase
Each great turn of human history is a turn of the staircase. Fire came first, with the earliest secure traces of burning at a human site about a million years old. Farming came within the last 12,000 years; industry over roughly the last two centuries; and the digital world, as smartphone ownership among American adults rose from 35% in 2011 to 91% in 2025. Each turn improved the view. Each also made the way back down harder, as more people, buildings and habits came to rest on the new level.
Each turn improved the view, and made the way back down harder. Most chapters of the book count what one turn cost a particular system.
- Topic 3
Fire was the first turn, and cooking was its dividend.
- Topic 7
Shoes came late on that climb, and padding only at the industrial turn.
- Topic 8
The Tsimane are climbing, in a few decades, a turn that took industrialized nations generations.
- Topic 10
The recent turns may be making blocked noses more common.
- Topic 13
Maycoba now began to climb a turn that Arizona had climbed a century before.
- Topic 14
Its lower turns were never chemically quiet, and neither is your plate.
- Topic 18
Hay fever arrived with the industrial turn.
- Topic 19
If the authors are right, pale European skin is partly a product of the agricultural turn.
- Topic 20
The agricultural turn brought grain and cities, and with them the crowd diseases, such as measles (Chapter 4).
- Topic 21
The industrial turn did not invent the aching back.
- Topic 22
The turn that gave women control over when, and whether, to have children also carried their old hormonal defenses outside the range they evolved for.
- Topic 30
The digital turn did not attack the default network directly.
- Topic 32
The industrial turn filled the world with molecules the hormone system had never been asked to read.
- Topic 33
The nuclear household, one adult and one infant behind a closed front door, belongs to a recent turn.
- Topic 35
Every turn that added years also decided what those years would be made of.
- Topic 38
Most of its chapters count what each turn has cost.
- Topic 39
The recent turns did not arrive one system at a time.
How the claims on this site are graded
Every recommendation in the book, and every one in the register on this site, carries a mark for the strength of the evidence behind it. The definitions are the book's own.
- StrongEvidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.59 recommendations
Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.
- ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.127 recommendations
Good observational evidence with a plausible mechanism, or small or few trials.
- EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.48 recommendations
Early, small, animal-only, or actively contested.
A ●○○ item is worth trying when it is cheap and safe. It is not worth rearranging a life around. See all 234 graded recommendations.
Where the evidence is strongest
Of the 234 graded recommendations in the book, 59 carry the strong mark: multiple randomised trials, or consistent large cohort studies with a well-understood mechanism. A sample, each linked to the chapter that argues it:
- Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.Train balance and strength, especially after 60Topic 7
- Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.Move through the day, every dayTopic 8
- Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.Raise your ceilingTopic 8
- Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.Eat for potassiumTopic 8
- Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.If you salt at home, swap the shakerTopic 8
- Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.Keep salt under 5 g a dayTopic 8
- Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.Know your numbersTopic 8
- Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.With lymphedema, work with a specialistTopic 9
- Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.Eat more fiber, from more kinds of plantTopic 12
- Evidence grade: Strong. Multiple randomized controlled trials, or consistent large cohort studies with a well-understood mechanism.Move for insulin sensitivity, not to burn off foodTopic 13
The case against
The book gives a whole chapter to the argument against itself (Topic 38), and every other chapter carries a Skeptic's Corner. The strongest objections are worth stating plainly:
The stories outrun the evidence.
In 1971 a short Lancet paper described blood fats in Inuit on the west coast of Greenland. It became the Eskimo diet, then the omega-3 hypothesis, then fish oil in every pharmacy. In 2014 a team led by J.G. Fodor found that the studies behind it had never investigated how common coronary artery disease was in that population at all.
Ancient bodies were not free of modern disease.
About a third of ancient mummies scanned for the purpose showed hardened arteries.
Chronic pain is not modern.
The Tsimane of Bolivia, forager-horticulturalists with no office chairs, report chronic pain at rates within the range of industrialised countries. What differs is what comes after the pain: disability.
Living foragers are not ancestors.
The Hadza are modern people. By one estimate fewer than 200 still follow the traditional foraging life, and their gut diversity belongs to a whole way of life, hardships included, that few outsiders would choose.
Not everything old was better.
Across tens of millions of deaths in hundreds of locations, cold accounted for far more temperature-related deaths than heat. Home air conditioning explains essentially the whole fall in United States deaths on hot days over the twentieth century.
Marlene Zuk's Paleofantasy is the strongest book-length argument against this frame, and it is on the reading list.
Common questions
- What is evolutionary mismatch?
- Evolutionary mismatch is the gap between the world a body evolved in and the world it lives in now. A body reads signals from its surroundings, movement, light and darkness, microbes, heat and cold, food and other people, and was built for the versions its ancestors met. Modern life gives it too much of some, too little of others, and much that is new. In that gap, researchers suspect, lie many chronic diseases.
- Who came up with the idea of evolutionary mismatch?
- S. Boyd Eaton and Melvin Konner proposed it in their 1985 paper Paleolithic Nutrition, which its authors later called the first publication of the evolutionary discordance hypothesis. In 1988, with Marjorie Shostak, they published Stone Agers in the Fast Lane, which supplied the word: humans today are Stone Age hunter-gatherers displaced through time, and the resulting mismatch fosters diseases of civilization. Daniel Lieberman later popularised the idea. James Neel's 1962 thrifty-genotype paper is the earlier ancestor of the thought, though the thrifty-gene hypothesis itself has fared badly.
- Is evolutionary mismatch accepted science?
- In a 2018 consensus exercise, experts in evolutionary medicine gave mismatch 93% agreement as a core principle of the field. That is agreement on the principle, not on any particular mismatch claim. A specific claim still has to pass the tests below, and many popular ones do not.
- How do you test whether something is really an evolutionary mismatch?
- A 2023 team set out three tests. The condition must be more common or severe in the new environment than in the old. It must be tied to a specific environmental factor that differs between them. And there must be a mechanism, ideally a gene variant with a history of selection that helps in the old setting and harms in the new. The same team added that today's subsistence peoples are not themselves ancestral populations.
- Does evolutionary mismatch mean we should live like hunter-gatherers?
- No. Foraging peoples alive today are modern people, not ancestors, and their health advantages come bundled with a whole way of life, hardships included. The useful claim is narrower: particular signals a body evolved to expect can be restored deliberately, and the evidence for restoring them varies from strong to contested, signal by signal.
- What is the strongest argument against evolutionary mismatch?
- That the story is easy to tell and hard to check. The Inuit omega-3 case is the standard warning: a 1971 survey of blood fats in Greenland became a global claim about heart disease, and in 2014 a team found that the question everyone assumed had been answered, whether coronary artery disease was actually rare in that population, had never been asked. Chronic back pain is another. The Tsimane of Bolivia, forager-horticulturalists with no office chairs, report chronic pain at rates within the range of industrialised countries.
The full argument
The whole body and mind, in sixteen practical chapters
This page is the summary. The book takes each part of you in turn, states what it evolved to expect and what it gets now, and ends every chapter with a protocol, every recommendation graded.