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Why We Get Sick
Chapter 6. Toxins, New, Old, and Everywhere
There are lots of novel toxic hazards to which we are exposed. There is alcohol, agricultural pests, nitrates, toxic dust and fumes, spray insecticides that enormously harm our health day by day. It seems obvious that our modern age must be more hazardous than that one our ancestors lived in. But this is not true because the contest between consumer and consumed can generate an evolutionary arms race.
Most plants contain toxins that would be harmful if eaten in more that a minimal amount. These toxins keep herbivores from eating the plants that are poisonous. As they find way around any one defense, the arms race creates many new ones. That is why the list of different toxins and their various effects is huge and impressive. However, all adaptations have costs. The plant may have either high toxin levels or rapid growth, but not both simultaneously. Seeds are often especially poisonous because they are the means of reproduction strategy. Nectar is designed to repel the wrong visitors and not to discourage the right ones. Nuts have hard shells to protect them from many animals. Plants developed so numerous and varied escalations of the arms race. However they do not have a nervous system, plants receive signals that alarm them of what takes place in a small region. There are dozens of different kinds of toxins, each with its own way of interfering with bodily function. The plant-herbivore arms race has created weapons and defenses of enormous power and diversity.
But what about human body? Many swallowed toxins can be rendered harmless by stomach mucous layer. If they are absorbed, they are transferred to the liver, the most important detoxification organ. If we overload our body with toxins, those in excess circulate through the body, doing damage whenever they can. With toxins our bodies can adapt to chronic threats but not to occasional ones. We limit our consumption to prevent overloading with toxins and thus minimize the damage by instinctive diversification, as well as with our own special array of detoxification enzymes. We can protect ourselves also by learning about what we eat and how poisonous it is. Our cultural heritage and cooking traditions also prevent us from being poisoned. Selective breeding allows to lower or eliminate the level of toxins in particular species.
Novel toxins are of high importance because they are absolutely different chemically from those that people are able to cope with. Moreover, we have no natural inclination to avoid some novel toxins. Our body does not have system of identification of artificial toxins. And we are wrong if we expect that some chemical agencies will assess the risks and protect us from being poisoned. The rat tests held there have low reliability and many difficulties.
Mutagens and chemicals cause mutations. They lead to cancer or damage genes that my result in birth defects or death. But people vary in their susceptibility to many substances and thus have different vulnerability. This vulnerability may differ by age and sex.
As we remember, natural selection does not serve a purpose of making people happy. It's purpose is to make us more fertile. That is why morning sickness of pregnant woman may also be explained as a natural device to minimize fetal exposure to toxins. At the same time anything that suppresses morning sickness may cause birth defects. Such things as any drugs, alcohol, cigarettes are best to be avoided while pregnancy too. It is better to be safe than sorry.
Chapter 7. Genes and Disease: Defects, Quirks, and Compromises
Our bodies don't work very well. We are bundles of genetic flaws and physicians' job is to fix these nature's oversights. That is why it is important to understand what genes do. DNA stores and uses information to build a body. It is difficult to imagine the amount of information in the genetic code. 95% of DNA is never translated into proteins, other 5% can be divided into subunits called genes. The goal of scientists now is to unravel the entire code to compare the genes of any individual to those in the standard sequence. About 7% of our genes differ from person to person. Some of genes have different versions that work identically. In other cases, one version is normal and other is defective. Often the defective gene is recessive that means it has little influence compared with normal one. If it is dominant, it may cause a disease.
The question is why genes make these diseases possible and why the natural selection does not cope with these threats. The answer partly is rareness of defects and comparatively little harm compared to ones caused by more common genes selected despite they cause more serious disease. Errors in generation genetic code are not more common. In most cases mutations have no detectable effects, in others they cause minor effects and in a few they are really fatal. While the body grows, the possibility of errors increases. A mutation of a single cell may lead to huge problems if it knocks out some crucial part of the mechanism. Thus a single cell may lead to tumor creation that jeopardizes the whole organism.
We know quite a lot about genes but still it is only scattered islands of understanding in a vast sea of ignorance. A single complete complement of genes is called genome. Having two parents, everyone must have two copies of each gene, two complete genomes and they constitute the genotype. In the organism we observe the phenotype that is the genotype influenced in the individual development by many external and internal factors. Genes interact with one another and with the environment in determining the features of a phenotype.
Most of diseases are caused from recessives if an individual received two copies of them. Natural selection cannot eliminate a deleterious regressive gene. Situation with recessive genes mutations is indeed that situation where the power of natural selection is limited. Dominant genes have another matter because if you have even one copy of a gene that causes a disease, you will definitely get this disease and so do half of your children. Such genes are not eliminated by the natural selection because the diseases caused by them, for instance the Huntington's disease, do not affect the reproductive rate.
Some useful genes can cause disease too. They are not eliminated because they give heterozygote advantage when some people who are homozygote get the disease. Thus, a gene that causes a lethal childhood illness and a gene that makes one susceptible to malaria can both be maintained at high frequencies in the population. If a gene were to decrease the chances of miscarriage even slightly, it could be selected for even if if also increased the risk of developing a disease. There are also outlaw genes that act for their own benefit but harm both the individual and the species.
Some diseases are the result of many genes or what chromosomes they are on. The possibility of their occurrence may depend on both genes and environment. Myopia is a classic illustration of a disease whose cause is simultaneously strongly genetic and strongly environmental. As genes like those that lead to myopia caused no trouble for our ancestors, they are called not defects but quirks.
No one DNA code is ideal and all of them have deviations. Even when a person is genetically exposed to a particular kind of disease, he or she needs environmental influence for it to become apparent. That is why we should not be scarred by our genes.Chapter 8. Aging as the Fountain of Youth
Aging is one of the most terrible thing that is continuously happening with everyone. It reminds people of inevitable death that await its time. Still people have hope to find a cure from aging, but unsuccessfully. Despite life expectancy has steadily increased, life span has not. It seems that aging as a disease is incurable. Technically, we speak not about aging but about senescence, the process of bodily deterioration. It is accompanied by lots of diseases and a decreasing ability to repair damage. From an evolutionist's point of view, an individual who did not senesce would have a substantial reproductive advantage.
If this process is so much devastating, why natural selection does nothing to eliminate it. Logically, the maintenance of one body is easier than forming a new one. Despite our bodies do have some capacity to repair damage and replace worn-out parts, this capacity is limited. Our bodies can not be maintained indefinitely. Senescence starts not at forty or fifty but with far more subtle changes shortly after puberty. Such systems as heart, lungs, kidneys, neurons have similar rates of deterioration. Senescence is not a disease, it is just a result of decline of every bodily capacity that makes a body vulnerable to a myriad of diseases.
Senescence is an evolutionary mystery. It is necessary to make room for new individuals so that evolution could keep a species abreast of ecological changes. The existence of menopause is a related mystery. The ability to have additional children ceases by the age of fifty in order to mother would be able to pay more attention and care to existing children. Our bodies are perfect systems because they are well-throughout. Some senescence genes have early benefits. Moreover, the genes with early benefits contribute to senescence. The whole immune system is age biased.
There are several mechanisms that lead to senescence and limited longevity. Damage by free radicals, blood levels of uric acid, DNA damage lead to senescence but our body can eliminate their effects to certain age. This ability is designed by natural selection to maximize the reproductive success. Moreover, these mechanisms of senescence differ from species to species. Aging differs by sex too. Women have advantage of longevity over men. The reasons are again in the domain of reproduction. Male reproductive success is so dependent on competitive ability that male physiology is devoted more to this competition and proportionately less to preservation of the body.
Biologists and evolutionists say that senescence is not a mistake but compromise carefully wrought by natural selection. That is why hopeful talks about life span increase are just hopeful talks. Senescence serves its mission. But if gerontologists stop trying to find the fountain of youth in some single, controllable cause of senescence, their efforts may prove more fruitful fro human well-being. The preoccupation with living forever is better to be substituted be a desire to live as much full live as possible and within time frame while it is possible.
Chapter 9. Legacies of Evolutionary History
Our air-food traffic problem has no functional reason. The only one responsible for it is our remote ancestor. The animal was too small to need a respiratory system. As it evolved, a respiratory system evolved too. But evolution proceeds by slightly modifying what it already has done. That is why additional respiratory capacity was created by slow modifications of food sieve. Later, evolution of our breathing system caused some other changes that we now are forced to regret. The human capacity for choking represents an ancient maladaptive legacy aggravated by a much later compromise.
This flaw is not the only one that makes humans susceptible to medical problems. Inside-out retina or eye's blind spot are universal defect that also make no functional sense. The appendix is another example. It has stopped serving its function and thus until it has not entirely disappeared, the vestige makes us vulnerable to appendicitis. Natural selection gradually reduces the size of it but this in turn makes us even more susceptible to this disease. Other examples are humans' inability to produce their own vitamin C and predisposition to some mechanical damage. The increased skull size gives some troubles for women while they deliver a child.
The prevalence of maladaptive human design features has been recognized for a long time. Our knees, ankles and feet are particularly vulnerable. Upright posture poses challenges to our digestive and circulatory systems. Some of flaws serve their mission bringing the benefits in youth but taking revenge when we get older.
Many design features, while not maladaptive, are functionally arbitrary and explicable only as historical legacies. They can cause many problems but some of them can be exploited. Moreover, many of our adaptations such as immune system are superior to those in other mammals.
The key point of the above-mentioned information is that we are specifically adapted to Stone Age conditions. The evolution and natural selection had no time to adapt us to the world we live now.
We are, in the words of some distinguished American anthropologists, “Stone Agers in the fast lane.” Our ancestors could live in better environmental conditions, but they also experienced difficulty and hardship. Death always balanced reproduction. Mortality rates in the Stone Age were highest in infancy and declined throughout childhood. Our ancestors were exposed to much more infections and for them they almost always turned out to be lethal. They faced shortages of food and vital necessities.
Human nature was formed in the environment of evolutionary adaptedness, or EEA. Anthropologists differ in their views on what it was like because of the shortage of information. The correct answer probably would be it varied. There is no one “natural” way of human life. Social systems were influenced by the physiological and structural differences between the sexes. Thus, the physiological costs of reproduction are borne by women while economic costs apportioned to their husbands or male relatives. These physical differences provoked behavioral differences. Economic necessity often implied that some kind of division of labor with women specializing on gathering and men on hunting. Despite access to fruits and berries, there were times of actual starvation. However, that air pollution from which we suffer now cannot be compared to odors of a Stone Age. If we happen to be a hut with a fire on the floor, we would not be able to bear those conditions. They were able to experience such things as kinship and friendship considering them as a source of pleasure and security. And despite all struggles of those times, they still were able to find reasons for laughter.
Chapter 10. Diseases of Civilization
In the last chapter we described that it is irrational to think that our ancestors had better conditions than those ones we have now. Agriculture, domestication of animals, other technological advances for exploration of distant lands and transportation led to greater freedom for lots of people. But many of the advantages we enjoy today are mixed blessings. Such threats as cancer are now more dangerous than they were a few generations ago. The reason for it is longer life duration. Our ancestors simply did not live till their bodies became more vulnerable to illnesses like this one.
Unfortunately, the consequences of aging are not the only bad aspects of the better life we live today. Invisible genetic quirks can cause more variation in phenotypes and some of this variation may be abnormal. This happens mostly because a vulnerable genotype encounters new or unacceptable environment. We also changed the way we get food and this led to shifts in our environment. This, in turn, increased the population density, but became a source of new problems.
Shifts in our tastes and nutrition preferences due to new ways of food production alleviated the possibility of actual starvation but put the danger of diseases caused by unhealthy food or imbalanced nutrition. That is why some of the diseases are diseases of civilization. They existed long time ago but were caused by different reasons. Shortages of specific vitamins and minerals arose in just the past ten thousand years or so. Today we understand the importance of vitamins and if we consume wide range of fruits and vegetables, we get enough of them. The modern concern is not the deprivation but an excess of nutrition.
Overeating is a matter of concern now. Modern overnourishment is mainly the result of steady long-term overeating. Our dietary problrms arise from a mismatch between the tastes evolved for Stone Age conditions and their likely effects today. An overwhelming amount of preventable disease in modern societies results from the devastating effects of a high-fat diet. The most important thing people can do to improve their health is to cut the fats out of their diet. The traces of exotic chemicals are much less dangerous than things overwhelmed with fats that we consume every day. Moreover, some people have genes that provide an ability to get and store food energy with unusual efficiency. That is why some people seem to be more prone to overeating than others.
Excess eating is not easy to deal with and some efforts can do harm instead of helping. Food restrictions may lead to intensified hunger or resetting of the basal metabolism. Moreover, almost every effort to deceive our body by eating artificial sweeteners and non-nutritive fat substitutes ends with wrong signal to our systems that provokes intensified hunger and so on. A diet that is too high in calories and fat for one person may be ideal for another. Today we have different approach to energy compared to our ancestors: we face endless source of energy supply while they were adapted to conserve it as much as they can.
Substance abuse is another major problem of our times, however opium and alcohol were in supply long time ago. Our society suffers from technical innovations that made these substances more addictive. Thus, alcoholism and other substance abuse can also be considered diseases of civilization. Lack of adequate exercise such as jaw exercise may also be a problem. Crowded and misplaced incisors and imperfectly erupted wisdom teeth may be diseases of civilization. Other problems such as lower back pain may be a result of sitting for hours on chairs. Some physicians even see high blood pressure as a disease of civilization because it is needed to supply larger bodies compared to bodies of our ancestors. There are much more factors that now may lead to diseases of civilization. Again and again we harp on th themes that all benefits have costs and that many benefits are worth their associated costs.
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