Although our evolutionary heritage has saddled us with some significant health problems, in the long run it has served us well…



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Diseases of Civilization

  • Although our evolutionary heritage has saddled us with some significant health problems, in the long run it has served us well…

  • Our cultural evolution has saved us from the fate of our distant ancestors

  • No longer locked into lives that were short and brutal, toiling dusk ‘till dawn to survive

  • Modern medicine, despite its many problems, has added years to our lives, reduced child mortality to very low levels

  • At the same time, we’ve created many new environments in which pathogens flourish

  • We’ve provided many new opportunities for pathogens to spread

  • We’ve adopted new cultural lifestyles which affect our bodies in ways evolution did not prepare it for

  • Many pathogens have greatly benefited from human civilization

  • Fleas, ticks, and lice that sought refuge in our furs and fabrics

  • Rats and mice that fed in our fields and storage bins

  • But cultural evolution has given us new weapons in the eternal war against microbes

  • We are no longer helpless in the face of epidemic disease

  • An army of experts is on hand to deal with emergent and re-emergent diseases

  • But many of our remaining health problems may be our own doing

  • Who will protect us from ourselves?

  • These new diseases spring from the lifestyles allowed by modern society

  • They are diseases of civilization…

  • Consider the endless hours of repetitive motion required by farm labor throughout society’s history

  • Now mostly replaced by repetitive motion at the mouse and keyboard

  • Arthritis, carpal-tunnel syndrome, are diseases of civilization

  • Analysis of ancient bones shows that arthritis became much more common when agriculture replaced hunting and gathering

  • In ancient nomadic communities, arthritis was mainly confined to the very elderly

  • No longer the case today…

  • Diseases of civilization include:

  • Cancer

  • Rickets

  • Dental caries (tooth decay)

  • Obesity

  • High blood pressure

  • The transition from tribes of nomadic hunter-gatherers to settled agricultural and urban communities changed the human race forever

  • One of the most significant changes in our cultural evolution is the change in our ancestral diet

  • This change in diet created many nutritional problems, including tooth decay

  • Our dental fillings are a mute testimony to our transition to an agricultural society, in the Neolithic

  • Dental caries is caused by bacteria, which cling to the teeth, secrete acid

  • Studies of ancient remains shows significant tooth wear, but little decay

  • Tooth decay is still rare today in cultures like the Inuit who don’t eat a lot of grain

  • Cooked grains, especially wheat, are very sticky, cling to the tooth surface

  • Sticky film on our teeth is a perfect habitat for tooth decay bacteria

  • Combination of wheat, sugar, and milk is like a bacterial smorgasbord…

  • Abrasion of raw food (ancient diet) wears teeth down more quickly, but also scrapes off the bacterial buildup, prevents decay

  • Modern agriculture is the source of many of our chronic health problems

  • Consider that classic New World combo, corn and beans…

  • Corn (maize) and beans formed the staple diet of many New World cultures, still true today in many regions

  • Nutrionally sound, from the point of view of proteins

  • Need to get or make all of the 20 amino acids our bodies use to make proteins

  • Corn and beans between them have all 20 amino acids, in addition to carbohydrates and fats

  • Southern US natives switched to a corn/beans diet ~1,500 years ago

  • Made nutrition easier, with reliable crops, healthy protein diet

  • But not as healthy as the diet of their hunter-gatherer ancestors

  • Ancestral skeletons of southern natives are more heavy set, fewer nutritional problems evident in their bones

  • Corn and beans is great for proteins and carbohydrates, but lacks some essential vitamins and minerals

  • Milk is another nearly perfect food, with milk sugar (lactose), fats, and plenty of high-quality protein

  • Designed by evolution to nurture the young of mammals (Latin word “mamma” means breast)

  • Digestion of milk sugar (lactose) requires a special enzyme, protein called lactase

  • Lactase breaks lactose down into two simpler sugars which babies can digest

  • After weaning, the lactase gene is switched off in all mammals, body can no longer process milk sugar

  • Human babies are born able to digest lactose

  • Presumably, our ancestors were like other mammals, and lost that ability after weaning

  • Before the days of soy milk (~ 30 yrs. ago), babies who couldn’t digest mother’s milk were dead babies

  • Strong selective pressure for being able to digest milk sugar before weaning

  • No selective pressure to retain that ability after weaning (mother’s milk was the only source)

  • But many human races, unlike other mammals, remain lactose-tolerant after weaning

  • In lactose-intolerant people, milk sugar is not digested, provides rich food for tummy bacteria, get severe digestive problems

  • F.J. Simoons (1978) looked at 197 populations from around the world, and found a very interesting pattern

  • Lactose-tolerant populations were concentrated in particular ethnic groups

  • They were mainly northern and western European races, and their New World and Australian descendants

  • Included also were a few African, Mideastern tribes

  • Durham (1991) chose 60 populations to represent the full spectrum of human agriculture:

  • hunter-gatherers

  • crop farmers

  • dairy farmers

  • mixed dairy/non-dairy ancestry

  • Clearly shows the relationship between type of subsistence and lactose tolerance

  • Dairy tribes tend to be very lactose tolerant, hunter-gatherers and non-dairy tribes tend to be lactose-intolerant

  • African-Americans are mostly lactose-malabsorbers (= lactose intolerant)

  • Populations considered to be “lactose malabsorbers” are those where 70% or more have trouble digesting lactose

  • 73% of African-Americans are lactose-malabsorbers to some degree, vs. 16% of the white population (Lockwood and Caldwell 1995)

  • African-Americans are mostly descended from tribes that did not raise cattle for milk

  • No one knows when dairy farming began

  • Maybe 5-8,000 years ago…

  • Did the regular availability of animal milk as food select for the ability to digest it after infancy?

  • Perhaps, perhaps not…

  • There is a widespread cultural solution to lactose-intolerance

  • Many dairy cultures use milk in the form of cheese and yogurt

  • Cheese and yogurt are OK for lactose-intolerant people

  • In the fermentation of milk, bacteria change lactose to lactic acid, or back into simpler sugars

  • Use of cheese and yogurt is widespread, but has not always selected for lactose intolerance

  • Some cheese/yogurt cultures are lactose intolerant, some are not

  • And the percentage of lactose tolerant dairy farmers, though logical, is high (over 90%)

  • Durham reasoned that these inconsistencies suggested a deeper pattern

  • There must be an additional source of evolutionary pressure selecting in favor of lactose tolerance

  • And therein lies a tangled tale…

  • Durham went back to his original study, this time looked at where lactose-tolerant groups lived

  • Found a strong correlation with latitude - lactose tolerant groups were more northern

  • Why did latitude correlate so strongly with lactose tolerance?

  • Before we can solve this puzzle, we must first consider another curious way in which cultural evolution has caused disease

  • It began hundreds of thousands of years ago, when we first migrated north, out of Africa…

  • Cultural evolution allowed our species to establish itself in parts of the world where more primitive man could not survive - high latitudes, high altitudes

  • These places are mostly cold and dark…

  • Ability to make fire, build shelters, skin animals, enabled us to move to higher latitudes

  • Many people today live in very cold climates…

  • Living in colder, darker climates has caused some interesting and unusual health problems

  • Our distant African ancestors lived mostly outside, in the open, lots of sunlight

  • Dark skin pigment is an adaptation to such high-UV equatorial environments

  • Risk of sunburn, skin cancer is reduced by high levels of the protein melanin in the skin (same protein gives hair/eye colors)

  • The level of melanin in the skin is an evolutionary trade off, a compromise…

  • Humans also need an important substance called Vitamin D

  • There’s no shortage of Vitamin D in Africa, created by sunlight striking cells in the skin

  • As long as your skin isn’t too dark, you can both synthesize Vitamin D, and be protected from excess UV

  • When we moved north, we changed the rules…

  • Now we were living in environments that were cloudier, lower intensity sunlight, so we had less of a UV problem

  • But less sunlight also meant less Vitamin D

  • To make matters worse, we stayed indoors a lot more

  • And when we did venture out, we bundled up against the cold, not much exposed skin

  • Even in more temperate climates, sun bathing is a relatively recent thing

  • Our ancestors didn’t have much spare time to indulge in it…

  • Lack of Vitamin D causes the nutritional deficiency disease known as rickets

  • Used to be called the English disease, it was so common in British populations

  • Bones become soft, weak, abnormal bone development, young victims esp. get characteristic bow-legged stance

  • Victims bones are so soft as they grow, they bend outward under the child’s weight

  • Vitamin D is important for good health

  • Helps calcium transport from the small intestine to the blood

  • Controls calcium deposition in growing bones

  • Helps maintain adult bone structure

  • Natural selection favored lighter skin pigmentation in climates where sun exposure was reduced

  • Stopped favoring darker pigmentation, no need for heavy sunblock

  • Started actively selecting for lighter skinned individuals who could absorb enough sunlight to get plenty of Vitamin D

  • Skin pigmentation represents an evolutionary balance between two conflicting selective pressures

  • Darker skin provides better UV protection, but restricts Vitamin D synthesis

  • Lighter skin allows more synthesis of Vitamin D but doesn’t provide as much protection from UV

  • But not all fair-skinned races suffer from chronic Vitamin D deficiency

  • Norwegian and Japanese don’t have this problem

  • Their fish diet is very high in Vitamin D

  • Ricketts was a major problem in the US until the 1930’s, especially high among young African-Americans

  • Government decreed that dairy farmers must add Vitamin D to milk

  • Reduced incidence of rickets…


  • Still a problem in the US

  • Which brings us back to Durham’s problem, why does latitude correlate so strongly with lactose tolerance?

  • Mothers synthesize the lactose in breast milk from two simple sugars, glucose and galactose

  • Babies must use lactase to break the lactose down again before they can use it…

  • Why not just give the kid straight glucose??

  • Lactose also helps the transport of calcium from the intestine to the blood - just like our old friend Vitamin D

  • In effect, lactose can substitute for Vitamin D in the diet in building strong bones (Durham 1991)

  • Northern cultures cover themselves up, dietary lactose helps to compensate for that (in addition to being great baby fuel)

  • So northern latitude dairy farmers could compensate for their reduced exposure to sunlight by drinking milk after weaning

  • Inuits eat a diet high in fish, so they get lots of Vitamin D

  • They can be lactose-intolerant and still survive bundled up at high latitudes, little exposure to the sun, without getting rickets

  • Some North-African/Arabian dairy tribes are also lactose-intolerant

  • Their infants get a lot of intense sunlight, no selective pressure to tolerate lactose after weaning, plenty of Vitamin D from the sun

  • Cheese or yogurt for food, no need for liquid milk after weaning

  • So selection for lactose tolerance may be primarily determined by the ability to get natural Vitamin D

  • The ability to get Vitamin D closely correlates with latitude

  • African-Americans aren’t the only ones with a lactose problem, over 90% of Asian-Americans are lactose intolerant

  • Does that mean the Vitamin D added to milk to prevent rickets does not help these populations, which can’t drink milk?

  • Yes and no – many substitutes, like soy milk, lactase pills or liquid can help

  • Can also “grow out of it”

  • Lactose intolerance is rare in babies under the age of two – why??

  • Lactase gene still switched on!

  • Usually kicks in around age 5-7, can get worse or better

  • Taking small amounts of milk etc. can build up a tolerance, often fades away on its own

  • Even breast milk is not perfect solution

  • Not enough Vitamin D for those with darker skin pigmentation

  • Increasing rate of rickets now reported in African-American mothers who breastfeed

  • Natural selection often works in such subtle and unexpected ways

  • Sometimes the problems it creates are not so subtle

  • The biggest problems agriculture has created for human health have something in common - too much of a good thing

  • Sheer quantity and variety of food available to most humans today is without parallel in human history

  • For better or worse, we can pick and choose as much or as little of any food we want

  • Often the choices we make seem to be very maladaptive…

  • We load up on sugars, fats, salts, etc…

  • Bring on those cheetos…

  • Unfortunately, our bodies did not evolve to handle such high levels of nutrition

  • Today's staples were yesterday’s luxuries

  • All of the items forming the bulk of our modern diet were in short supply on the African plain

  • Meat, fat, sugar, salt were rare treats for our ancient ancestors

  • There’s absolutely nothing wrong with sugar, or salt, or fat, or meat…we’d be hard pressed to survive without them

  • Healthy natural diets often contain high amounts of all these things

  • Getting these things on the plains of Africa meant the difference between life and death

  • Big selective pressure in early human evolution to get as much of these items as possible

  • That’s why they taste so darned good - the body’s little reward for a job well done…

  • We still want as much of these things as we can get

  • But it’s no longer such a great idea, now that they’re readily available in infinite supply

  • Creates several big health problems…

  • Consider the effects of excess dietary fat

  • Fat is high-energy food, calorie rich

  • Good way to store extra calories in the body, for a rainy day

  • Normal cycle in the wild is feast and famine, fatten up to get through winter

  • Now we have a uniformly high food supply all year long

  • And at the same time, our general activity has dropped to very low levels

  • It’s no longer adaptive to be lazy…

  • Once upon a time, long, long ago and far, far away, being lazy was a good idea

  • Our ancestors needed to conserve their energy for hard times, or bursts of power or speed to escape predators

  • Now we are lazy all the time - not such a great idea any more

  • Very few urban jobs require substantial physical activity - mailman, garbage man, construction…

  • Most are sedentary - retail sales, secretaries, clerical work, computer work…

  • Combination of low activity levels and high-fat diet is a prescription for obesity

  • Excessive dietary fat can cause or contribute to

  • Heart attack

  • Stroke

  • Arterial blockage

  • Diabetes

  • Cancer risk

  • Getting excess dietary fat is almost inevitable, even in a “normal” American diet

  • Wild game is ~15% fat, pampered cattle have much more fat (~20% or more)

  • Average hunter-gatherer got ~20% fat in diet

  • Average American diet gets 40% of its calories from fat!

  • Couple this high-fat diet with physical inactivity, and you’re living the American Dream!

  • Two thirds of the American population is overweight or obese

  • American male = 191 lbs (25 lbs more than in 1960)

  • American female = 164 lbs (20 lbs more than in 1960)

  • Roughly 39 million Americans are obese, 30 pounds or more above their optimal weight

  • LA#5 among states for obesity

  • Obesity contributes to 300,000 deaths a year

  • Obesity costs the American public a cool $147 billion a year in health and related costs

  • Also costs ~ one billion extra gallons of gasoline to carry our big butts around!

  • Jan.’03 lawsuit vs. McDonalds thrown out

  • Way too much of a good thing…

  • Spring 2004 - WHO guidelines launched an international effort to control obesity

  • Reduced sugar, salt, fat in processed food

  • Tighter control of food commercials aimed at children

  • Better nutrition labeling

  • Better nutrition education

  • Federal and state initiatives may finally be working

  • 2014 federal report – obesity in children (2-5 yrs) has dropped 43% during the last decade


  • There are many similar examples of how our basic American diet is at odds with our African evolutionary heritage

  • Pima Indians of Arizona are poor, have frequent famines

  • Food assistance in modern times has created a big problem…

  • Pima have exceptionally high levels of obesity and diabetes

  • Their bodies evolved to handle a greatly restricted diet

  • Japanese immigrants have a similar problem

  • Japanese traditional diet is high in fish, low in fat

  • Japanese-Americans have over twice the incidence of heart attacks as native Japanese, and much higher levels of serum cholesterol

  • The classic “food pyramid” has been recently reformulated, to encourage better dietary choices

  • But a recent discovery may render it somewhat academic…

  • Chronic high blood pressure is another major modern health problem

  • One of the primary contributing factors is excess dietary salt

  • Larger body size, stress, also contribute

  • Our average body size is larger than it used to be - blood pressure is adjusted to a lower range of body sizes

  • Brain not quite caught up with regulating blood pressure in larger bodies

  • Stress of modern life also adds to high blood pressure


  • It has been a mere 10,000 years since we forsook the role of hunter-gatherer for the staid and settled world of agriculture and urbanization

  • In some ways, our bodies still live on the great plains of Africa…

  • Our daily environment has changed radically in the scant millennia of our human civilizations

  • In evolutionary terms, our bodies have not always kept pace with many of these environmental changes

  • We must cope with these new environments as best we can, in bodies designed over millions of years for a vanished way of life


Directory: ~bfleury -> darwinmed -> darwinmedlectures
darwinmedlectures -> Although our evolutionary heritage has saddled us with some significant health problems, in the long run it has served us well…
darwinmedlectures -> The 1918 Flu 1 – a conspiracy of Silence
darwinmedlectures -> Germ Theory
darwinmedlectures -> In our last lecture, we looked at the ways that trade, travel, technology and agriculture can provide new habitats and new dispersal routes for microbes
darwinmedlectures -> The Evolutionary Arms Race Remember the Red Queen in Alice in Wonderland?
darwinmedlectures -> The 1918 Flu 2 The Philadelphia Story
darwinmedlectures -> The 1918 Flu 1 – a conspiracy of Silence
darwinmedlectures -> So say the Laws of Manu, an ancient Brahmin text on moral conduct Man is a moral animal…
darwinmedlectures -> Pandora's Box Remember the legend of Pandora's Box?


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