Summary

Bill Bryson provides a comprehensive and engaging exploration of the human body and its intricate workings. Bryson delves into a wide range of topics from the history of medicine and the discovery of DNA to the various systems and organs. He weaves together scientific research, historical anecdotes, and personal observations to create a compelling narrative that is both informative and thought-provoking.

Key Takeaways

• 59 elements in body, 24 “essential”
  • 99.1% are 6 elements: C, O, H, N, Ca, P
  • ~$100k to build human from elements
• 70kg man: 40L of water
  • Base: 1.5L/day via sweat, breath, urine
  • Vigorous exercise: 1.5L/hour
• Brain holds 2 exabytes of knowledge
  • Brain only needs 400 cals/day, 15W
  • Short-term memory: 30 seconds, 6 items
• 6 universal emotions: fear, anger, surprise, pleasure, disgust, sorrow (smile)
• As many as 33 total senses (time, satiety)
• Taste core components: sweet, salty, sour, bitter, umami
  • Possibly also: metal, water, fat, kokumi
  • Smell is 70-90% of flavor (eg. strawberries)
  • Sight, sound also contribute to taste
• Types of nociceptors (pain): thermal, chemical, and mechanical
• Mismatch diseases: caused by modern lifestyle in contrast to hunter gatherer evolution
• 40% of people will get cancer
• Deaths: 20% immediate, 20% quickly, 60% slow decline
• Life expectancy
  • Increases for elimination:
    • Cancer: 3.2 years, heart disease: 5.5 years, Alzheimer’s: 19 days
  • Since 1990, only 10/12 months added to average lifespan are healthy
  • Lifespan past 80 is almost purely genetics

Notes

1: How to build a human

• 59 elements in body, 24 “essential”
• 99.1% are 6 elements: C, O, H, N, Ca, P
• ~$100k to build human from elements
• ↑ estimates vary widely though
• 200k-1m different proteins in body

2: Skin and hair

• Skin: 20 ft.², 15 pounds
• 2-5 million hairs, 4-10 million sweat glands
• Different types of touch sensors, but no wetness sensor
• Dark skin evolved separately multiple times (convergent), as did back to light skin
• Light hair, eyes only over last 5k years, no benefit beyond attractiveness
• Hair has growth cycles 4 weeks - 7 years
• 70kg man: 40L of water
  • Base: 1.5L/day via sweat, breath, urine
  • Vigorous exercise: 1.5L/hour
• Losing 3-5L: lethargic
• Losing 6-7L: mental impairment
• Losing 10L: death (7-45 miles of walking)
• 60% of men bald by 50, 20% by 30

3: Microbiome

• Micro biome: 3 pounds
• Viruses, fungi (molds, yeasts), protists
• Antibiotic-resistant superbugs

4: Brain

• Brain holds 2 exabytes of knowledge
• Brain only needs 400 cals/day, 15W
• 86 billion neurons
• Brain forecasts 0.5 seconds in the future
• Synthesizes asynchronous sensory input
• “Color isn’t a fixed reality, but a perception”
• Short-term memory: 30 seconds, 6 items
• Brain has shrunk 10% (tennis ball)

5: Head

• 6 universal emotions: fear, anger, surprise, pleasure, disgust, sorrow (smile)
• Genuine smiles cannot be faked: eye muscle contractions
• Micro-expressions for 0.25 seconds beyond our control: can be taught to spot them
• Chin, eyebrows purely for beauty
• As many as 33 total senses (time, satiety)
• Eye can identify 2-7 million colors
• 1 million million times amplitude audible range
• Between 10,000 and 1 trillion different smells
• Smell is highly unique to individuals

6: Mouth and throat

• 400 newtons of bite force
• Taste core components: sweet, salty, sour, bitter, umami
  • Possibly also: metal, water, fat, kokumi
• Umami / MAG is recent in western world
• Smell is 70-90% of flavor (eg. strawberries)
• Sight, sound also contribute to taste

7: Heart and blood

• 3.5 billion heartbeats in life
• 15% of blood goes to brain, 20% to kidneys
• Safe blood pressure 140/90 → 130/80
• Heart disease deaths: 600/100k (1950) → 168/100k (2019)
• Blood: red cells, white “”, platelets, plasmas
• Bleeding: how wrong our assumptions can be based on current science
• Blood types more effective against certain diseases, diversity beneficial for species
• Quest to develop artificial blood to carry oxygen unsuccessful thus far

8: The chemistry department

• Insulin, pituitary gland
• Endorphins, testosterone,
• Hunger: leptin and ghrelin
• Liver, gall bladder, etc.
• Kidney: manages sodium, blood pressure
• ↑ effectiveness drops by 50% from 40→70

9: Skeleton

• Normally 206 bones, but varies
• Hands and feet have over 1/2 body’s bones
• Bones produce hormones which help with cognitive function, thus exercise is good
• Tendons: muscle to bone, ligaments: bone
• Tendons: low blood supply → long heal time
• 600 muscles, 40% muscle by mass
• Muscle uses 40% of BMR
• 120 steps/minute
• 8.5% bone by weight

10: Bipedalism and exercise

• Humans have high walking economy
  • Chimps use 4x the energy
• Long distance running is our specialty
• Walking 6 million years ago, running only 2 million years ago
• NEAT is a big factor for weight management
• Almost all mammals have about 800 million heartbeats in life (except humans which now last 3x longer)

11: Equilibrium

• Hypothalamus manages equilibrium
• 1° rise in body temp = 200x slower virus replication
• Body temp is a trade off (2° = 20% more)
• Cell electrical signals = bolt of lightning
• Use equivalent in our weight in ATP daily
• Unit 731 experiments

12: Immune system

• B and T cells are main actors
• Helper, killer, memory T cells
• Organ transplant and skin grafting
• 50+ types of autoimmune diseases

13: Lungs and breathing

• 5% of adults have asthma (30% in England)

14: Food

• Vitamins: organic, minerals: inorganic
• 97% of people don’t get enough potassium
• Fiber lowers cholesterol levels
• Modern fruits are more sugary, less nutritious than before selective breeding
• More sodium is likely worst for people with existing hypertension issues
• Have a sensible approach to food

15: Guts

• Average time food spends in body:
  • Men: 55 hours, women: 72 hours
• Stomach can hold about 1.4 liters
• Appendix could be storage for gut bacteria

16: Sleep

• All animals seem to sleep
• Elephants and giraffes need 2 to 3 hours sloths need 10 hours
• Third set of cells in eyes to measure brightness for circadian rhythm

17: Sex differences

• Y chromosome shrinking, gone in 4.7m yrs, sex gene will move to new chromosome
• 15-25% adultery rate
• College males think about sex 1x per hour
• Sex differences under-accounted for in medicine etc.
• Mitochondrial DNA only from mother
• ↑ share a common mitochondrial ancestor from as little as 20k years ago
• Penis size: 5-7 inches, 4.5-5.8 inches

18: Conception and birth

• Chance of conception: 3%
• 6m eggs in womb, 1m at birth, 160k in child bearing years
• 8x risk of allergies with C-section, increased risk of obesity and diabetes

19: Nerves and pain

• Types of nociceptors (pain): thermal, chemical, and mechanical
• A and C fibers: A immediate pain, C slow throbbing pain
• Spiciness triggers heat nociceptors
• Types of pain: nociceptive (stimulus, good), inflammatory, dysfunctional, neuropathical
• Chronic pain has no purpose
• 4% of people have never had a headache
• 40% of people are in chronic pain
• US is 4% of world population but 80% of opioid use
• Placebos are incredibly powerful

20: Diseases

• Smallpox was most prolific pandemic in history, first virus to be completely eliminated
• Mismatch diseases: caused by modern lifestyle in contrast to hunter gatherer evolution

21: Cancer

• 40% of people will get cancer
• Prostate cancer almost inevitable for men
• 80 year old is 1000x more likely to develop cancer than a teenager
• Mustard gas → chemotherapy

22: Medicine, good and bad

• Increased longevity, but unfairly distributed
• 50% of medical treatments unnecessary

23: Death

• Deaths: 20% immediate, 20% quickly, 60% slow decline
• 90% of people reach their 65th birthday
• Life expectancy increases for elimination:
  • Cancer: 3.2 years
  • Heart disease: 5.5 years
  • Alzheimer’s: 19 days
• Since 1990, only 10 of 12 months added to average lifespan are healthy
• Over 300 scientific theories for aging:
  • Genetic mutation
  • Wear and tear
  • Cellular waste accumulation
• Lifespan past 80 is almost purely genetics