3. Constraints
There are many things that natural selection just can’t do. No system can replicate genetic information with perfect accuracy, so mutations happen. Natural selection cannot upend the laws of physics, so there will never be flying elephants. Selection cannot make bodies that generate their own energy. These constraints apply to any system, natural or mechanical.
Path dependence also limits the perfection of machines as well as bodies. Once things have gone down a certain path, there may be no starting over. Your computer keyboard is an example. You could shift to a more efficient key arrangement, but only at a great cost of relearning and incompatibility with existing keyboards.
Changing substandard aspects of the body is even less likely. The vertebrate eye is often held up as a model of perfection, but it has gross design flaws. Vessels and nerves come through a hole in the back of the eyeball, creating a blind spot; then they run between the light and the retina. They could just come through the back of the eye wherever they are needed, as they do in the octopus eye. But they don’t. Natural selection cannot fix the design defect in the eyes of vertebrates because any such transition would create thousands of generations of blind individuals.
Our brains are also jury-rigged. They are prone to all kinds of thinking errors.54,55 Some persist for the same reason that the eye has a blind spot; it is impossible to start over and do it right. Even aside from path dependence, much of our vulnerability to mental disorders results from the limits of what selection can do. Mutations happen.
4. Trade-offs
Nothing in the body can be perfect, because making one trait better will make something else worse. You can buy a car that accelerates to 60 mph in four seconds, but it won’t get fifty miles per gallon and it will not carry eight people. You can get a sunroof on your car, but only at the risk of rain leaking in. You can get tires made with sticky rubber that are fabulous on ice—I highly recommend them for Michigan winters—but they are expensive and short-lived and they make handling squishy.
The body is a bundle of trade-offs.56,57,58,59,60 Everything could be better, but only at a cost. Your immune system could react more strongly, but at the cost of increased tissue damage. The bones in your wrist could be thick enough that you could safely skateboard without wrist guards, but then your wrist would not rotate and you could throw a rock only half as far. You could have an eagle’s ability to spot a mouse from a mile away, but only at the cost of eliminating color vision and peripheral vision. Your brain could have been bigger, but at the risk of death during birth. Your blood pressure could be lower, at the cost of weaker, slower movement. You could be less sensitive to pain, at the cost of being injured more often. Your stress system could be less responsive, at the cost of coping less well with danger.
In every case, both extremes pose disadvantages. The best cost-benefit ratio comes at some middle level. Too much sensitivity to pain or anxiety is bad, but so is too little. Natural selection is not usually changing things; it is usually keeping things the same, at some middle level. Life without pain or anxiety seems attractive, but it would often be short.
5. Reproduction
The body is not shaped for maximum health or longevity; it is shaped for maximum transmission of its genes. Alleles (different versions of a gene) that increase the number of offspring become more common over the generations, even if that shortens life and increases suffering. This is not merely theoretical. Half of the human population has been shaped by selection to live fast and die young.61 I mean, of course, the fragile sex. On the average, men die seven years sooner than women do. From ages zero to ten in developed countries, for every 100 girls who die, 150 boys die. At puberty and shortly thereafter, the ratio is 300 men for every 100 women.62,63 Why? The proximate explanation involves testosterone and its effect on tissues, immunity, and risk taking. The evolutionary explanation is that allocating effort and resources to competition instead of tissue repair increases reproduction more for males than females; males who win competitions get more mates and have more offspring.
The costs are not, however, only for men. Females also sacrifice health for reproduction, just not as much as men do. All organisms are shaped to behave in ways that increase fitness even if that decreases health and happiness. Did you ever desperately want to have sex with someone even though you knew that could lead to disaster? Most people have, with sometimes dire consequences. Then there are the rest of our desires and the inevitable suffering because they cannot all be fulfilled. We want so badly to be important, rich, loved, admired, attractive, and powerful. For what? The good feelings from succeeding are just about balanced by the bad feelings from failure. Our emotions benefit our genes far more than they do us.
6. Defensive Responses
People seek help mainly for symptoms, not diseases. Pain, fever, malaise, cough, nausea, vomiting, and diarrhea are protective responses. So are anxiety, jealousy, anger, and low mood. They are set off when something bad is happening. They are unpleasant but useful. If you have pneumonia, you had better hope that your cough reflex works well; otherwise you are likely to die. You had also better hope that your doctor knows that cough is useful and does not prescribe too much medication that blocks your cough excessively.
Nonetheless, doctors routinely prescribe drugs to block normal defense responses. Thank goodness! Blocking unnecessary pain, nausea, cough, and fever makes life much better. However, there is a mystery here. If defenses are useful responses shaped by natural selection, you would expect that blocking them would usually make people sicker. Why don’t people die like flies after taking medications that block normal defenses?
I thought about this for several years before finally finding a solution— the Smoke Detector Principle.64,65 Most of the responses that cause human suffering are unnecessary in the individual instance but still perfectly normal because they have low costs but protect against huge possible losses. They are like false alarms from smoke detectors. The occasional wail when you burn the toast is worth it to ensure that you are warned early about every real fire. An occasional experience of unnecessary vomiting or pain is worth it to ensure protection against poisoning or tissue damage. This is why it is usually safe to use drugs to block vomiting and pain.
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If you are a lumper, you may have already noticed that these six reasons for vulnerability can be collapsed to three. Mismatch and coevolution cause problems because bodies evolve too slowly to keep up with changing environments. The next two reasons are things selection just can’t do; selection is constrained, and everything is subject to trade-offs. The last two are not exactly reasons why we are vulnerable to disease; they are misunderstandings about what natural selection shapes. Selection maximizes reproduction, not health, and the unpleasantness of defenses such as pain, cough, and anxiety is just part of their utility.
Disease and Evolution, Not
Trying to find evolutionary explanations for vulnerability to disease is a challenging enterprise prone to mistakes. As mentioned in chapter 1, Viewing Diseases As Adaptations (VDAA) is the most common and most serious mistake in evolutionary medicine. So several cautions bear repeating. Diseases themselves do not have evolutionary explanations. They are not adaptations shaped by natural selection. Genes or traits associated with some diseases provide advantages and disadvantages that influence natural selection. However, proposals about the utility of diseases themselves, such as schizophrenia, addiction, autism, and bipolar disorders, are wrong before they start. The correct question is Why did natural selection shape traits that make us vulnerable to disease?
Such vulnerabilities need an evolutionary explanation using some combination of these six factors. There is a tendency to seek a single explanation, for instance, blaming all problems on modern environments or on trade-offs or constraints. Usually, however, multiple factors contribute. For instance, an evolutionary explanation for atherosclerosis includes modern
diets, the role of infection in causing inflammation, and the benefits and costs of immune activation in arteries. Finally, evolutionary explanations are not alternatives to explanations that describe mechanisms; both are necessary. Evolutionary explanations for vulnerability to disease are crucial to helping us understand why mental disorders exist at all and how to find their causes and better cures.
PART TWO
Reasons for Feelings
CHAPTER 4
GOOD REASONS FOR BAD FEELINGS
There is . . . a time to weep and a time to laugh, a time to mourn and a time to dance . . . a time to love and a time to hate.
—Ecclesiastes 3:4 (New American Standard Bible)
One of the pleasures of antique shopping is trying to fathom the functions of mysterious machines. The one I am looking at is mottled cast iron. A crank on one side rotates a vertical slotted disk through a little cup. Even after examining all the parts and cranking the handle, I can’t figure out what it is for, so I ask the seller. “It’s a cherry pitter,” he explains. Of course! Knowing its function makes instant sense of its form. Cherries fall into the slots, and a plunging rod pokes out the pits. Knowing that purpose reveals that this one is broken—the crank does not turn smoothly. Even in working condition, it would not help much nowadays; the slots in the wheel are far too small for modern megacherries.
Emotions provoke perplexity for the same reason as the cherry pitter. They have been described in extraordinary detail, but what they are for remains uncertain. Basic questions remain controversial. What are emotions? Ten experts will give you ten different answers. How many basic emotions are there? Pick any answer, and you can find an expert who will agree. How can we decide when an emotion is abnormal? Agreement on an answer is impossible without knowing the benefits and costs of each emotion in different situations. What causes emotional disorders? Some blame the brain, others blame diet, infection, conditioning, thinking habits, psychodynamics, or social structures. Debates about emotions generate emotions: fury and frustration. Stepping back to observe the fray arouses others: alienation and hopelessness.
Several obstacles make understanding emotions difficult. Failing to recognize that negative emotions are useful is a big one. Another is failing to realize that emotions were shaped to benefit our genes, not us. A fundamental obstacle is not recognizing that describing mechanisms provides only one-half of a full explanation. However, perhaps the biggest obstacle is thinking about emotions as if they were part of a designed system. That makes it seem as if each emotion should have a different function. However, each emotion has many functions, and many functions are served by multiple emotions. Different emotions correspond not to different functions but to the different situations each was shaped to cope with.
Pain and Suffering Are Useful
People usually seek treatment not because they know they have a disease but because they are suffering. They go to general physicians seeking relief from pain, cough, nausea, vomiting, and fatigue. They go to mental health professionals seeking relief from anxiety, depression, anger, jealousy, and guilt. The clinical approach to such symptoms differs dramatically.
Imagine that you are a doctor working in a medical clinic, evaluating a young woman who complains of abdominal pain that has become gradually worse over the past couple of months. She says the pain is cramping or aching in the mid to lower part of her abdomen. It tends to be worse at night but doesn’t seem to be related to when or what she eats or her menstrual cycles. She is generally healthy and takes no medications. You ask more questions and schedule tests to try to discover the cause. Is it cancer, constipation, irritable bowel syndrome, or an ectopic pregnancy? You assume that the pain is a symptom and that finding the cause will provide the key to a cure.
Now you are working in a mental health clinic, evaluating a young woman who complains of constant worry, poor sleep, lack of energy, and loss of interest in most activities, even caring for her previously spectacular garden. The symptoms began a couple of months ago but worsened enough in the past few weeks that she finally came for help. She is generally healthy and takes no medications. She denies drug use, drinking, and recent major life stressors. You are likely to assume that the negative emotions themselves are the problem and to prescribe treatment to relieve the symptoms.
It is deeply ironic that so-called biological psychiatry, with its commitment to what is called “the medical model,” uses only half of biology and a model very different from that in the rest of medicine. In general medicine, symptoms such as pain or cough are recognized as useful responses that indicate the presence of a problem. They spur a search for the cause. In psychiatry, symptoms such as anxiety and low mood are often presumed to be the problems themselves. So instead of searching for what might be arousing anxiety or low mood, many clinicians instead assume that they are pathological products of a broken brain or distorted thinking.
The general human tendency to ignore the effects of situations and to attribute problems to characteristics of individuals is so pervasive that social psychologists have a name for it: “The fundamental attribution error.”1 It is exemplified by the DSM, in which symptoms of anxiety or depression that are intense enough for long enough are sufficient to diagnose an emotional disorder, no matter what life situation a person is in.
Social scientists Allan Horwitz and Jerome Wakefield suggested a way to reduce this error. They pointed out that the DSM-IV excluded the diagnosis of depression after the recent loss of a loved one, so they suggested including similar exclusions for other severe life events.2 The DSM-5 authors acknowledged the inconsistency, but their solution was to eliminate all exclusions, even the one for recent loss of a loved one.3 They said this was necessary for consistency and because intense bereavement symptoms sometimes indicate depression that needs treatment. They also wanted to avoid the unreliability that would result if diagnosis required judging the severity of life events.
The tendency to assume that symptoms are disorders is also a problem in the rest of medicine, where it has been called “the clinician’s illusion.”4 Symptoms seem as though they are the problem because they are so distressing and disabling. Pain can make life agony. Diarrhea can cause fatal dehydration. Such symptoms seem unnecessary because it is usually safe to use medications to block them. However, pain, diarrhea, fever, and cough are all useful in certain situations. Each is expressed normally when the relevant situation is present and, as the Smoke Detector Principle points out, when it might be present. Excessive expression is abnormal. Deficient expression is less obvious but equally abnormal. Whether a response is normal depends on the situation.5,6,7
Many responses adapt bodies to changing situations.8,9,10 Physiologists study the mechanisms that adjust breathing, heart rate, and body temperature to changing situations.11,12,13 Behavioral ecologists study how cognition, behavior, and motivation changes adapt organisms to shifting situations.14,15,16 Like sweating, shivering, fever, and pain, capacities for fear, anger, joy, and jealousy are useful in certain situations.17
The very idea that negative emotions can be useful can seem preposterous to those who are experiencing them. To get beyond such understandable skepticism, here are four good reasons for thinking that symptoms have evolutionary origins and utility. First, symptoms such as anxiety and sadness are, like sweating and coughing, not rare changes that occur in a few people at unpredictable times; they are consistent responses that occur in nearly everyone in certain situations. Second, the expression of emotions is regulated by mechanisms that turn them on in specific situations; such control systems can evolve only for traits that influence fitness. Third, absence of a response can be harmful; inadequate coughing can make pneumonia fatal, inadequate fear of heights makes falls more likely. Finally, some symptoms benefit an individual’s genes, despite substantial costs to the individual.
Emotions Are for Our Genes, Not Us
It was a warm summer evening in 1975, and I was settling in for a ni
ght in the hospital as the doctor on call. There were no problems on the ward and the ER was calm, so I started reading Edward O. Wilson’s new book, Sociobiology. It was nearly midnight when I encountered a sentence that left me gobsmacked:
Love joins hate; aggression, fear; expansiveness, withdrawal; and so on; in blends designed not to promote the happiness of the individual, but to favor the maximum transmission of the controlling genes.18
In a flash, I realized that my view of behavior and emotions was wrong. I had thought that selection shaped us to be healthy, happy, nice, cooperative members of a community. Alas, no. Natural selection does not give a fig about our happiness. In the calculus of evolution, only reproductive success matters. I had been treating emotional disorders full-time for a decade without knowing much about normal emotions. After a night of unsettled sleep, I decided to educate myself. The next day I looked up emotions in my psychiatry textbooks. I found only vague smatterings that aroused confusion and boredom. Those emotions did their job, and I turned my interests elsewhere.
Soon after, a student came for help in controlling his jealousy. It was urgent, he said, because “My girlfriend is gorgeous, and I will never get another chance to have a woman like her. We have been living together for a few months, but she says she will leave if I don’t stop acting so jealous. I have got to stop it.” He vividly imagined her kissing another man but said he had no reason to suspect that she was unfaithful. He sometimes followed her to see if she was really going to work, and he made up excuses to call and check on her whereabouts. He was not psychotic or depressed.
Good Reasons for Bad Feelings Page 6