抑郁症病人。 （图 | 来源于网络）

导语：After centuries of discredited quackery,evolution may suggest a way to understand mental illness.

选自葛朗台App

《经济学人》-19年第15周-P78

“Your whole field is confused. You know that, right?” The patient who delivered this parting shot had a perpetual knot in the pit of her stomach. She had lost interest in everything, was anxious, irritable and nauseous, and struggled to sleep. Her family doctor had told her it was “nerves”. A psychotherapist asked about sexual feelings in childhood for her father. A psychiatrist offered drugs to fix what he said was a chemical imbalance in her brain.

Confused and desperate, she had found her way to yet another doctor, an assistant professor of psychiatry. Anxiety can be useful, he told her, but most people experience more than they need—because whereas too much merely makes you miserable, too little can make you dead. She was stuck in a cycle of worry, heightened vigilance and more worry. Cognitive behavioural therapy, which teaches people to break corrosive thinking patterns, would help. She brightened up—and offered a few home truths about the psychiatrist’s profession. 

Randolphe Nesse, now of Arizona State University, cites that encounter in his fascinating book to illustrate why he has spent his career studying the evolutionary roots of mental illness. Though doctors who treat physical ailments do not routinely refer to evolution, their theories about bodies are based on the fact that humans, and the pathogens that afflict them, are the product of aeons of natural selection.

Disorders are defined by comparison with normal functioning. Symptoms such as rashes, fevers and pain are understood to be consequences of, or defences against, illness, not the illness itself. Treating an ailment like diabetes, in which a complex system malfunctions, means knowing how that system is supposed to work—and what it evolved to do.

Mental-health specialists lack such solid foundations. In general, they neither study the feelings of the well, nor consider what feelings are for. Of the 4,500 pages in America’s most popular psychiatry textbook, normal emotions get half a page. Moreover,whenitcomesto diagnosis, they fail to consider underlying causes.

The current version of the American “Diagnostic and Statistical Manual for Mental Disorders” (dsm-5) defines hundreds of disorders solely by their symptoms. Depression, for example, means at least two weeks experiencing five or more of eight symptoms, such as loss of pleasure in life, loss of appetite and feelings of worthlessness. The diagnosis is the same if you have just been bereaved or divorced or lost your job.

In Dr Nesse’s definition, “specialised states that…increase the ability to meet adaptive challenges” constitute normal emotions. They are experienced as positive or negative because only situations containing opportunities or threats affect evolutionary fitness. A negative emotion may be just as evolutionarily useful as physical pain.

A depressed patient’s low mood, for example, may result from his realisation that a major life project is sure to fail. It feels terrible, but makes sense in evolutionary terms. People who do not suffer when pursuing unachievable goals may waste their energies on pointless effort, thereby harming their chances of reproduction. That insight taught Dr Nesse to ask the depressed: is there something very important that you are trying and failing to do, but can’t bring yourself to give up?

Evolution has equipped people for a world very different from the one they now inhabit. They are obese because their appetites are adapted to scarcity, not superabundance. Similarly, some mental ill-nesses may be the result of having to negotiate situations they are not fit for. Others may be side-effects of selection for desirable traits. Dr Nesse draws an analogy with racehorses, bred for speed with the unfortunate result that their cannon bones are brittle. For every 1,000 that start a race, he says, one breaks a leg and has to be put down. It may have slightly weaker bones than the rest. Or it may simply be unlucky and stumble. Humans may have “minds like the legs of racehorses, fast but vulnerable to catastrophic failures”.

When it comes to doctoring the body, you have to go back to the 19th century to find a time when the theories were baseless (infections were caused by miasmas, for instance) and the treatments often harmful (bloodletting, purging and the like). For doctoring the mind, as Anne Harrington’s fine history of psychiatry shows, that point is much more recent.

In 1949 a Nobel prize went to the Portuguese inventor of the lobotomy, an operation intended to sever the “worry nerves” of the brain. In 1952 the technique was sufficiently honed for an American acolyte to launch “Operation Icepick”— a 12-day road trip during which 228 patients were strapped down and anaesthetised, before he or an assistant slipped an ice-pick-shaped knife under each eyelid and into their brains, and gave a twist.

What ended that practice was not an outbreak of compassion, but the arrival of thorazine, a drug that caused such mental deadening that it was nicknamed the “chemical lobotomy”. It was the start of the age of blockbuster drugs for mental illness. By the end of the 1950s one in three prescriptions in America was for meprobamate, which dampened anxiety. By 1990, 1m Americans received Prozac prescriptions each month. Pharmaceutical companies popularised the notion that anxiety, depression and so on were caused by chemical imbalances. Right them and you could become not just well, but better than well.

Under the influence of Freud, psychiatrists had sifted their patients’ life histories for repressed emotions and memories. But in the 1980s psychiatrists declared a post- Freudian world, with mental illnesses ascribed to brain biochemistry and neuroanatomy. They expected to discover the genes that caused mental illnesses, and bespoke drugs that could heal them.

That revolution never happened. Instead pharmaceutical firms are pulling back, as stricter testing rules reveal how little good many of their products do. The evidence linking mental illnesses to defects of brain architecture or chemistry, or to specific genes, is scanty. With its checklist approach to diagnosis, dsm-5 is under attack. Ms Harrington’s history ends with today’s crisis in the psychiatric profession. If Dr Nesse is right, evolutionary thinking could provide a fruitful new direction.

*文章为作者独立观点，不代表葛朗台立场。

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