Genome - Matt Ridley

levels, and the Cortisol will dash about the body busy switching on genes. (It is also an indisputable fact that you can trigger activity in the 'happiness centres' of the brain with a deliberate smile, as surely as you trigger a smile with happy thoughts. It really does make you feel better to smile. The physical can be at the beck and call of the behavioural.)

Some of the best insights into the way behaviour alters gene expression come from studies of monkeys. Fortunately for those who believe in evolution, natural selection is an almost ridiculously thrifty designer and once she has hit upon a system of genes and hormones to indicate and respond to stress, she is loath to change it (we are ninety-eight per cent chimpanzees and ninety-four per cent baboons, remember). So the very same hormones work in the very same way in monkeys and switch on the very same genes.

There is a troop of baboons in east Africa whose bloodstream Cortisol levels have been closely studied. When a certain young male baboon attached himself to a new troop, as male baboons of a certain age are wont to do, he became highly aggressive as he fought to establish himself in the hierarchy of his chosen society. The result was a steep increase in the Cortisol concentration in his blood as well as that of his unwilling hosts. As his Cortisol (and testosterone) levels rose, so his lymphocyte count fell. His immune system bore the brunt of his behaviour. At the same time his blood began to contain less and less of the cholesterol bound to high-density lipoprotein (HDL). Such a fall is a classic precursor of furring up of the coronary arteries. Not only was the baboon, by his free-willed behaviour, altering his hormones, and hence the expression of his genes, he was thereby increasing his risk of both infection and coronary artery disease.2

Among monkeys kept in zoos, the ones whose arteries fur up are the ones at the foot of the pecking order. Bullied by their more senior colleagues, they are continuously stressed, their blood is rich in Cortisol, their brains are low in serotonin, their immune systems are permanently depressed and scar tissue builds up on the walls of their coronary arteries. Quite why is still a mystery. Many scientists now S T R E S S 155

believe that coronary disease is at least partly caused by infectious agents, such as chlamydia bacteria and herpes viruses. The effect of stress is to lower immune surveillance of these dormant infections which allows them to flourish. Perhaps, in this sense, heart disease in monkeys is infectious, though stress may play a role as well.

People are very like monkeys. The discovery that monkeys low in the hierarchy get heart disease came soon after the far more startling discovery that British civil servants working in Whitehall also get heart disease in proportion to their lowliness in the bureaucratic pecking order. In a massive, long-term study of 17,000 civil servants, an almost unbelievable conclusion emerged: the status of a person's job was more able to predict their likelihood of a heart attack than obesity, smoking or high blood pressure. Somebody in a low-grade job, such as a janitor, was nearly four times as likely to have a heart attack as a permanent secretary at the top of the heap.

Indeed, even if the permanent secretary was fat, hypertensive or a smoker, he was still less likely to suffer a heart attack at a given age than a thin, non-smoking, low-blood-pressure janitor. Exactly the same result emerged from a similar study of a million employees of the Bell Telephone Company in the 1960s.3

Think about this conclusion for a moment. It undermines almost everything you have ever been told about heart disease. It relegates cholesterol to the margins of the story (high cholesterol is a risk factor, but only in those with genetic predispositions to high cholesterol, and even in these people the beneficial effects of eating less fat are small). It relegates diet, smoking and blood pressure - all the physiological causes so preferred by the medical profession — to secondary causes. It relegates to a footnote the old and largely discredited notion that stress and heart failure come with busy, senior jobs or fast-living personalities: again there is a grain of truth in this fact, but not much. Instead, dwarfing these effects, science now elevates something non-physiological, something strictly related to the outside world: the status of your job. Your heart is at the mercy of your pay grade. What on earth is going on?

The monkeys hold the clue. The lower they are in the pecking 156 G E N O M E

order, the less control they have over their lives. Likewise in the civil service, Cortisol levels rise in response not to the amount of work you do, but to the degree to which you are ordered about by other people. Indeed, you can demonstrate this effect experimentally, just by giving two groups of people the same task to do, but ordering one group to do the task in a set manner and to an imposed schedule.

This externally controlled group of people suffers a greater increase in stress hormones and rise in blood pressure and heart rate than the other group.

Twenty years after the Whitehall study began, it was repeated in a department of the civil service that then began to experience privatisation. At the beginning of the study, the civil servants had no notion of what it meant to lose their jobs. Indeed, when a questionnaire was being piloted for the study, the subjects objected to a question that asked if they feared losing their jobs. It was a meaningless question in the civil service, they explained: at worst they might be transferred to a different department. By 1995 they knew exactly what losing their jobs meant; more than one in three had already experienced it. The effect of privatisation was to give everybody a feeling that their lives were at the mercy of external factors. Not surprisingly, stress followed and with stress came ill health - far more ill health than could be explained by any changes in diet, smoking or drinking.

The fact that heart disease is a symptom of lack of control explains a good deal about its sporadic appearance. It explains why so many people in senior jobs have heart attacks soon after they retire and

'take it easy'. From running offices they often move to lowly and menial jobs (washing dishes, walking the dog) in domestic environments run by their spouses. It explains why people are capable of postponing an illness, even a heart attack, until after a family wedding or a major celebration — until the end of a period of busy work when they are in control of events. (Students also tend to go down with illnesses after periods of acute exam pressure, not during them.) It explains why unemployment and welfare dependency are so good at making people ill. No alpha-male monkey was ever such an S T R E S S 157

intransigent and implacable controller of subordinates' lives as the social services of the state are of people dependent on welfare. It may even explain why modern buildings in which the windows cannot be opened make people sicker than older buildings in which people have more control over their environment.

I am going to repeat myself for emphasis. Far from behaviour being at the mercy of our biology, our biology is often at the mercy of our behaviour.

What is true of Cortisol is also true of other steroid hormones.

Testosterone levels correlate with aggression, but is that because the hormone causes aggression, or because release of the hormone is caused by aggression? In our materialism, we find the first alternative far easier to believe. But in fact, as studies of baboons demonstrate, the second is closer to the truth. The psychological precedes the physical. The mind drives the body, which drives the genome.4

Testosterone is just as good at suppressing the immune system as Cortisol. This explains why, in many species, males catch more diseases and have higher mortality than females. This immune suppression applies not just to the body's resistance to micro-organisms, but to large parasites, too. The warble fly lays its eggs on the skin of deer and cattle; the maggot then burrows into the flesh of the animal before returning to the skin to form a nodule in which to metamorphose into a fly. Reindeer in northern Norway are especially troubled by these parasites, but males noticeably more than females.