The signal check

Every chapter, and what it expects

The full list the check draws on. Each line is a chapter's Mismatch Card: what that part of you expects, what the modern environment supplies instead, and how strong the evidence is.

• Chapter 2: What Your Body Expects, and How to Trust This Book

  ●●○Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

  Expects

  The signals its long past supplied without anyone arranging them: hours on foot, real darkness, varied food, microbes, heat and cold, and familiar people close by.

  Gets

  Too little of some signals (movement, daylight, fiber, company), too much of others (sugar, salt, evening light), and exposures that are new (nicotine is the classic example).

• Chapter 3: The Body That Walks

  ●●○Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

  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

  ●●○Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

  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

  ●●○Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

  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

  ●●○Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

  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

  ●●○Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

  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

  ●●○Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

  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.

• Chapter 9: Heat and Cold

  ●●○Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

  Expects

  Days and seasons that leave the comfortable band: cool mornings, warm afternoons, nights that cool, and occasional real cold and real heat.

  Gets

  A narrow indoor band all year, most of life spent inside, offices set for a man in a suit, and summers whose humid heat can outrun the body's cooling.

• Chapter 10: Green and Quiet

  ●●○Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

  Expects

  Daylight hours among plants, water and animals, and a quiet natural background broken by occasional sounds worth noticing.

  Gets

  Most of life indoors, a view of a wall, and mechanical noise that never stops, including at night, with bursts loud enough to damage the ear.

• Chapter 11: The Social Animal

  ●●○Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

  Expects

  Daily, face-to-face contact with a small, stable group; touch as an ordinary event; many hands around every infant, from labor onward.

  Gets

  A wide, thin network through a screen, inner circles left to chance, labor attended by rotating staff, and new parents largely alone behind a closed door.

• Chapter 12: Attention in the Age of the Phone

  ●●○Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

  Expects

  Rewards that are earned, spaced and often absent; long stretches with nothing to attend to; problems solved with your own equipment; and childhood days of free, mixed-age, outdoor play.

  Gets

  A pocket device engineered for time on device, paying out on a variable schedule and filling every gap; tools that supply the answer before the effort starts; and childhoods with hours of screens and the risk designed out.

• Chapter 13: Stress and the Mind

  ●●○Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

  Expects

  Threats that are physical, local and short, answered with the body, among allies who help solve problems.

  Gets

  Uncontrollable judgment without end, low control at work, long hours, thin company and short sleep.

• Chapter 14: Wanting, Loving, Losing, Meaning

  ●●○Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

  Expects

  Rewards that are scarce, variable and diluted; a partner and a small group met every day; losses mourned with others; a role the group depends on.

  Gets

  Pure, cheap, constant drugs and betting on a phone, with close relationships, mourning and purpose left to arrange themselves.

• Chapter 15: Women's Bodies Across the Life Course

  ●●○Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

  Expects

  A first period in the mid-teens, many pregnancies with long breastfeeding between them and about a hundred periods in a lifetime, food that matches effort, kin nearby, and a working body that carries loads through the transition.

  Gets

  Earlier first periods, fewer and later births, short breastfeeding and about four hundred periods; energy deficits in some and surpluses in others; grandmothers far away; and a transition lived mostly sitting down.

• Chapter 16: Aging Well

  ●●○Evidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

  Expects

  Daily physical work, food that comes and goes, constant company and microbes, and death arriving mostly from outside, after a modal age in the seventies.

  Gets

  Low physical load, constant food, tobacco and alcohol, and medicine that postpones death from diseases whose causes remain in place.

Common questions

What is the signal check?

It asks what an ordinary week of yours supplies, against what each chapter of the book says a part of you evolved to expect, and returns the gaps as a reading list of chapters, with the actions each chapter says to start with. It is not an assessment and not a diagnosis.

Why is there no score?

Because there is no validated instrument behind one. A number out of 100 would imply a measurement nobody has made. The output is a list of signals and the evidence grade attached to each.

What happens to my answers?

They stay in your own browser. Nothing is sent to a server, there is no account, and no answer leaves the device.

The book's own order for installing these is the 30-day protocol, which starts with the signals that cost nothing. For the longer treatment of any topic, see the reference library.