Although our evolutionary heritage has saddled us with some significant health problems, in the long run it has served us well…
Date 16.04.2016 Size 70.7 Kb.
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: 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 There were two big exceptions to Durham’s correlations 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… 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… 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 Share with your friends:
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