Women also seek other partners. Sometimes this results in additional pregnancies, but it more often provides other benefits, including resources, status, protection, and possibly better genes for offspring, in addition to pleasure.98,99,100 Men who try to prevent their partners from having such relationships will tend to have more children than men who are unconcerned about their partner’s sometimes being pregnant with another man’s baby. Male sexual jealousy reduces this risk, but at the cost of vast unhappiness, nasty fights, and much violence.101
Men and the power structures they erect use all kinds of strategies to try to control female sexuality. These strategies define, to a considerable extent, what a culture is like. The evolutionary historian Laura Betzig has devoted her career to studying the often sordid history of how men have controlled and used women’s sexuality.102 The rise of settled agriculture changed everything by making food storage and wealth accumulation possible.103,104 Men soon used their wealth to control other men, and especially women, in harems. Genghis Khan apparently had more than seven hundred, explaining why about 8 percent of Asian men carry descendants of his Y chromosome.105
The general pattern is skewed reproduction, with some men having considerably more offspring than others. This has always been the case to some degree, but new genetic analyses show drastically decreased diversity on the Y chromosome, starting about 10,000 years ago, reflecting a sharp increase in reproductive skew.106 That is about when the rise of agriculture made settled communities and wealth accumulation possible. The rise of market economies and complex societies that allow mobility changed things yet again so that groups of men now make and enforce rules that limit the ability of powerful men to hoard women.107 Finally, in a transition that is just now under way, birth control and financial independence have given women political power that they are using to free themselves from male domination.
These are, however, mere nomothetic generalizations. They provide a useful foundation for understanding why marriage and other sexual relationships are often so difficult and why sexual disorders are so common. However, they say little about the diversity of cultures, to say nothing of those among individuals and couples within cultures. They don’t begin to explain the complexities that swirl in most relationships. They do help to explain how a satisfying sex life with few difficulties is possible for many couples. Selection shaped mechanisms that make possible enduring committed relationships in which sex is one part of a rich tapestry woven over many years. An evolutionary perspective explains not only the prevalence of sexual problems but also the miracle of human love.
New Sex
New technologies are changing behavior, mores, and laws so fast that natural selection can’t begin to keep up. The biggest change is the advent of reliable birth control. No longer intrinsically tied to reproduction, sex has become a recreation for many. Prohibitions against sex before marriage and with multiple partners are no longer necessary to avoid pregnancy. Attitudes are changing fast. The percentage of Americans who think premarital sex is “not wrong at all” went from 29 percent in the 1970s to 58 percent in 2012.108 The fun is not risk-free. Control of sexually transmitted diseases looked, for a time, as if it would be reliably successful, but antibiotic resistance and epidemics of HIV and other diseases require condoms and caution more than ever before.
Another dramatic change is the earlier age at menarche, declining from an average age of sixteen to twelve.109,110,111 The brain, however, doesn’t mature any faster, so many people are wanting and having sex years before brains are ready to provide guidance.
Jealousy has decreased in the United States in recent decades, or at least its expression has become less acceptable,112 but it is still very much a part of our nature.113 Explaining its origins does not influence its power. I once heard a psychotherapist describe how he used his new evolutionary knowledge in couple’s therapy. “I just explain to them,” he said, “that men have built-in desires for sex with other women, so there is no need for a woman to get upset about occasional affairs.” He did not say how this worked, but it is easy to imagine it helped couples unite in agreement that they needed to find a different therapist.
New media make sexually arousing images unavoidable in public and pornography available in private. A remarkable number, well over 100,000 professionals and untold more amateurs, are doing it in front of cameras so millions can watch.114 The market for internet porn, estimated at about $40 billion per year a decade ago, has now shrunk dramatically, not for lack of interest but because so much is now free.115 The market for vibrators and other sex toys has exploded, with big implications for relationships, as they are marketed to women as routes to equal opportunities for independent sexual pleasure.116 Systems that allow remote control of vibrators via the internet make sexual interactions possible with partners thousands of miles away, although privacy may be an illusion; one manufacturer of such devices was recently found to be keeping records of episodes. Paying for sex remains against the law in many places, but fewer than before. Sex robots are just around the virtual corner.117
Where is sex headed? The only certainty is that new technologies are changing sexual options faster than cultures can change their traditions and far faster than natural selection can change our brains. I predict more pleasure, new problems, and better solutions informed by evolutionary explanations of why sex is both such a pleasure and such a problem.
CHAPTER 12
PRIMAL APPETITES
They are as sick that surfeit with too much as they that starve with nothing.
—William Shakespeare, The Merchant of Venice, 1596 (1.2.5–6)
Positive feedback is sometimes fun, sometimes disastrous. It is thrilling to watch a small snowball get enormous as it rolls downhill or grand fireworks set off by a single match. But runaway trucks and heart attacks are disasters. A tiny rupture in a bit of plaque induces turbulence in a coronary artery that causes clot formation, narrowing the artery, causing more turbulence and more clotting, until a completely blocked artery causes a heart attack. Positive feedback in anxiety and mood disorders causes similar spirals that can be almost as dire.
Vicious circles are central to explaining eating disorders. Excess weight causes joint pain, fatigue, and embarrassment that make exercise difficult, leading to more obesity and still less exercise, in a spiral to sickness. Eating sweets creates a desire for more sweets, in what has been called sugar addiction.1 Strains of bacteria in our guts that are fed straight sugar may manipulate us to eat the kinds of food that allow them to grow faster than other bacteria.2
Extremes and vicious cycles are prevented by systems that stabilize every aspect of the body. When body temperature drops, shivering turns on until the temperature is back to normal. When body temperature increases, sweating cools it down. Low blood sugar motivates eating and transforms starch stored in the liver into glucose. High blood sugar releases insulin, which moves glucose out of the blood and into cells. These systems work like thermostats to maintain homeostasis, the body’s stable state.
When something gets too high or too low, they turn on. When things are back in the normal range, they turn off. How many such systems are there? Thousands. They control large-scale functions such as blood pressure, heart rate, breathing, and eating. They also keep the levels of thousands of different chemicals and hormones and rates of cell division within narrow ranges. They even regulate when genes are turned on and off. Complex self-stabilizing systems are the essence of life.
Failures of homeostatic control systems are the essence of disease. The systems that regulate body weight now fail more often than not. The percentage of adults in the United States with normal body weight has plummeted from 55 percent in 1962 to 44 percent in 1990, 36 percent in 2000, and 32 percent in 2008. The percentage who are obese—over 210 pounds for a five-foot, ten-inch person—has more than doubled since 1962, from 13.4 percent to over 34 percent.3 In the United States, two-thirds of adults are overweight
or obese.4
We don’t need numbers to know we are overweight; we need only a mirror. So we decide to lose weight. Willpower should be able to control eating. After all, we make a conscious decision to open the refrigerator. We voluntarily open the ice cream and put it in a bowl. It can’t go down the hatch unless we lift a spoon and open our mouths. Even swallowing is voluntary. So millions of people decide to crank up their willpower and go on a diet.
Usually, weight declines for a few weeks or even months. However, 90 percent of the time weight goes back up, often above the starting point.5 Talk about pursuing an unreachable goal! Trying to control their weight makes millions of people feel terrible, not only about their bodies but also about their lack of self-control. Every day they (we) tell ourselves we will not overeat. Most days we fail, and we blame ourselves.
Failure to lose weight not only makes us less attractive, it also causes frustration, demoralization, low self-esteem, and justified fear of diseases and death. Compared to normal-weight people, obese people are 50 percent more likely to suffer from a chronic health problem.6 That is the same increased risk as aging from thirty to fifty and more than twice as much as being a smoker.7 It accounts for about 300,000 deaths in the United States each year.8
The solution seems obvious: try harder. We should be able to control ourselves. Eat less. Exercise more. Well-meaning professionals keep explaining this. Again and again. In magazines and books, on television and the internet. In your doctor’s office and your workplace. As if we didn’t know! But admonitions are not enough, so we pay for help. The weight-loss industry consumes about $60 billion per year in the United States alone, about half for products, half for services.9,10 Pills, diet foods, counselors, clinics, spas, surgery, and exercise programs thrive, to say nothing of thousands of inspirational books, each with its own special secret formula for weight loss. The proven benefits are few. There are so many competing solutions because none works very well.
A better solution depends on finding the cause. Research has been intensive. Thousands of articles offer possible explanations, each based on some possibly broken part in the weight control mechanism.11 Is it leptin? A genetic abnormality? Deep insecurity? Lack of early love? Trying to fill an empty place in the soul? Idealized images in magazines? Advertising? The microbiome? Lack of access to fresh, healthy food? Just not knowing what to eat? The surfeit of explanations documents the lack of reliable knowledge.
Here is a terse summary of what we know. The brain mechanisms that normally regulate eating are complex in ways that make intervention at any individual component unlikely to provide an easy solution. We cannot accurately predict who will become obese, but both genetic variations and social factors are important. We know the obesity epidemic in the United States took off in about 1980 and that many things changed about that time, including more sedentary jobs, fast food, new processed foods high in fat and sugar, artificial sweeteners, antibiotics, and mass media. It remains unclear if one of those bears primary responsibility, or if some combination explains the obesity epidemic. Whatever changed makes most of us overweight so reliably that the question of causes could be turned on its head: What is different about those peculiar people who maintain a normal weight?
Control systems work only within a certain range. Your laptop computer has systems that cool its circuits, but the fine print in the instructions says, “Use only in temperatures between 40 and 110 degrees Fahrenheit.” If you take your computer outside in the summer sun, the cooling system won’t keep up, and your computer will soon shut down. If you take your body outside in the summer sun without adequate protection and water, it, too, will soon shut down.
Our bodies are now exposed to fewer temperature extremes than our ancestors’ but more extremes of other kinds, especially food (high) and exercise (low). The systems that evolved to regulate eating protect against starvation superbly. When they detect a caloric deficit, they arouse hunger and extreme efforts to get food and eat it. Those who lack such systems are likely to die during even a brief famine.
The systems that protect against excess body weight are feeble by comparison. Genetic variations that made some people too heavy to escape Paleolithic predators have been selected away. However, the risks of predation because of being too heavy were smaller than the risks of being too thin. Even in modern societies, death rates rise faster for every pound underweight than they do for every pound overweight.12 So the brain mechanisms that protect against obesity are weaker than those that protect against starvation.
The main evolutionary explanation for the obesity epidemic is obvious: the mechanisms that regulate body weight are poorly suited for our modern environments. Taking your body into a modern grocery store is like taking your computer into the summer sun. The environment is outside the range that the control mechanisms can cope with. Our environment is so different from the one we evolved in that it’s remarkable that anyone eats normally. Our hunter-gatherer ancestors walked miles each day gathering food and hunting game, eager to satisfy hunger with whatever they could find. The food they found was mainly high-fiber fruits and vegetables and lean fish and meat. That was only a few thousand years ago, less for many populations.
Big changes have happened much faster than new control systems can evolve. The biggest change was the spread of agriculture about ten thousand years ago. Drought, fast-growing populations, and political conflicts still cause intermittent famines, but better storage, transportation, and economic systems have reduced the risk greatly. The next big change was the growth of cities, markets, and transportation, further increasing the amount and reliability of available food. Very recently, in just the past few decades, industrialization of food production has combined with marketing to provide people in many societies with whatever food they want whenever they want it. Finally, the human dream has been fulfilled!
The foodlike substances on grocery store shelves are a product of selection—not natural selection but selection by us. Food engineers combine fat, salt, sugar, carbohydrates, proteins, and chemicals into diverse shapes, colors, and textures. Their concoctions reach store shelves. We select what we want. Whatever we buy gets more shelf space and spurs imitators and variations that target our desires ever more accurately, like a heat-seeking missile homing in on a jet engine. Convenience stores display the results: row after row of potato chips, sugar-glazed nuts, chocolate-covered fruits, and double chocolate brownie premium ice cream. If you would rather not even chew, pick up a large Frozen Caramel Coffee Coolatta with Cream at Dunkin’ Donuts to get 990 calories in a single cup. The food products we take for granted are fantasies made real, available for pennies everywhere.
Alas, what we want is not good for us. Ask your doctor for diet advice. You already know what you will hear: you should eat plenty of vegetables and fruits, some complex carbohydrates, limited amounts of fatty meat, and minimal sugar. Or, more succinctly, “Don’t eat anything that you really like, eat only foods that don’t especially appeal to you.” The irony is unbearable. We have ready access to an infinite supply of foods shaped to precisely satisfy our desires, but consuming them makes us unattractive, frustrated, sick, and short lived.
As a result, millions now endure a daily torture worthy of Tantalus, the favored son of the Greek god Zeus. His first sin was, appropriately enough, introducing mere mortals to the god’s divine nectar and ambrosia. When the gods found out, they expressed their displeasure. As a spiteful pseudopenance, he invited them to a banquet and served them boiled bits of his son Pelops. The gods devised a diabolically appropriate punishment: Tantalus was chained eternally in a pool of cool, clear water that receded whenever he tried to drink. Figs, pears, and pomegranates dangling tantalizingly over his head were snatched away whenever he reached for them. The predicament aroused his thirst and hunger to a frenzy, never to be satisfied.
Our environments pose temptations worthy of Tantalus, but no chains restrain us. Willpower binds us as effectively
as wisps of thread. So we get momentary pleasure, followed by enduring shame and sickness. Worse yet, dieting resets the weight set point upward.13,14,15 It also slows down metabolism. For people who lost hundreds of pounds on the television show The Biggest Loser, eating a normal number of calories resulted in regaining weight, despite their still huge body mass.16 A few people, however, are capable of dramatically limiting their eating. Their problems are even worse.
Anorexia and Bulimia
I recall vividly the twenty-year-old woman admitted to our hospital at 70 pounds, headed for death within days because she would not even drink water. She was convinced she was obese and disgusting. In front of a full-length mirror, she saw a fat girl, but she looked to us like a concentration camp victim. For breakfast, she ate a single Cheerio with ostentatious ceremony, while looking condescendingly at those around her who lacked such self-control. I told her she did not have to eat anything right away but that she had to take water as a medicine. She agreed, and that stabilized her. We put her on a behavior therapy program that required regular eating, but she didn’t gain weight. Finally, we discovered a large plastic wastebasket in her closet filled with vomit. She survived and got back to a somewhat normal body weight after months of hospitalization, but she still thought about little except her weight, and she continued to gorge and vomit.
Bulimia is anorexia nervosa with less self-control. Like anorexics, bulimics try to restrict their food intake drastically, but they invariably lose control and gorge in feeding frenzies. Then they vomit, take laxatives, or pursue extreme exercise regimes. Bulimia is far more common than anorexia; fewer people have the self-control to not eat while starving.
Good Reasons for Bad Feelings Page 26