Thursday, December 20, 2007

How Social Hierarchies Affect Your Health

"One of the greatest challenges to public health is to understand the 'socioeconomic gradient'," says Robert Sapolsky, a primatologist at Stanford University.

Sapolsky has made a successful career of studying the effects of social position on health. Though he has studied mainly baboons, his expert synthesis of a broad range of studies on primate dominance hierarchies and health provides context for understanding how human social hierarchies affect health.

To him, the socioeconomic gradient refers to the finding that in Western societies, poor health is associated with lower socioeconomic status. He questions whether this is more due to unequal access to health care or to the psychosocial milieu of poverty. He also questions to what extent the stress of being poor affects health.

Groups of social animals form dominance hierarchies that produce pronounced inequalities in access to resources (food, territory, other individuals). An animal's rank can dramatically affect the quality of its life. A natural question to ask is whether low ranking or high ranking individuals are more stressed and consequently have poorer health.

In the 1950s, the concept of "executive stress syndrome" predominated. Until it was discredited, most people believed that for primates (including humans) high rank was more psychologically stressful. A decade later, the prevailing view held that low rank was more stressful. So what's going on?

Rank means different things in different primate species. I some species, high rank is more stressful while in others, it's low rank that kills - quite literally in some cases.

So which is it for humans? Think of the financially thriving alpha males and females out there who put in long hours as an executive and then come home and fix and plan meals, take care of children, etc. Are they more or less physiologically and psychologically stressed than people who live pay check to pay check, or are chronically under- or unemployed?

To predict whether we as a species would be in the the high rank = high stress or low rank = high stress group, we can look at the patterns that predict this for other primate species and question how those patterns apply to our species.

Resource Inequity: Despotic vs Egalitarian
Resource division depends on to what extent a species is despotic versus egalitarian. In despotic species, resources belong to those at the top and that is achieved through aggression and intimidation. In egalitarian species, resources are more evenly distributed and rank is achieved by the support of others.

Which human societies would you say are despotic, and which are egalitarian?

Social Rank Stability
Among primate species with ranking systems that are inherited, stable, and lifelong, (as in a caste system), lower ranked primates experience the most stress. In other species, rank constantly changes and is negotiated in what amounts to politics. When ranks change, the individuals who fight their way to get to the top experience the most stress. But, once they achieve their role as leader and can "boss" others, they calm down and then their subordinates experience the most stress.

In which human societies would you wealth is inherited and stable, and in which does income fluctuate widely and depend on what you do rather than to whom you were born?

How Rank is Maintained
For species in which rank changes and is achieved and maintained through physical aggression (e.g. ring-tailed lemurs), alphas are more physiologically stressed. Fighting is physically demanding. For species in which rank changes and is achieved and maintained through psychological intimidation (baboons, squirrel monkeys), lower ranked individuals experience more stress.

Which human societies would you say rank is achieved through aggression and which through intimidation? Do leaders become leaders by beating up others or through manipulation?

Breeding Style
Primates sometimes help rear each other's young. Usually these are older brothers and sisters who act as babysitters for their parents until they are old enough and experienced enough to attain territory and begin their own families (tamarins and marmosets). In these species, rank has little to do with stress. In most other primates species, the highest ranking males and females determine who actually breeds by aggressively monopolizing breeding opportunities. Subordinates are the ones who suffer, sometimes to the point of being infertile.

To what extent do you think people actively compete for a boyfriend/girlfriend, spouse, life partner so that they may begin raising a family?

Coping Strategies
How primates cope with stress is as important as whether they are stressed. The availability and efficacy of social support affects primate health in all species. However, not all species and individuals have equal access to social support. Among primates, social support takes the form of grooming, touch, and other forms of physical affection. These forms of contact provide the basis of alliances and reconciliation after conflict, which are also forms of social support. Because primates preferential groom family members, the presence of kin is an important. In some primate species, males leave their birth groups at maturity (e.g. puberty) to go live with another group. In these species, females are the ones in the group who are related. They support each other while unrelated males have few outlets for support. We call these primates 'female bonded.' The reverse is the case for species in which females leave their birth groups at maturity.

Which of these coping mechanisms are also beneficial forms of social support for people? To what extent are human societies male versus female bonded? What coping strategies have humans invented that are particularly harmful to health?

Stress -> Health
Without getting into a discussion of the physiological correlates of stress (specific hormones) and why they degrade the body, suffice it to say that stress diminishes health by producing:
* high blood pressure & elevated heart rate
* tighter, clogged arteries
* lowered levels of the 'good' cholesterol (HDL)
* higher levels of the 'bad' cholesterol (LDL)
* lower fertility
* lower immune system function
* altered brain chemistry (affecting memory and anxiety)

The answers to these questions can help us predict in which human groups, societies, and cultures people of low social rank or socioeconomic status are likely to experience the most stress and health problems. One aspect that makes humans somewhat unique among primates is that we don't form linear hierarchies. Instead humans belong to multiple kinds of groups and organizations in which rank varies. We also have internal standards we use to compare ourselves to others so that a person may feel poor or low ranked while occupying an objectively affluent or high ranking position. People may come to feel poor by their surroundings, especially where there are a few very noticeably wealthy people and much economic disparity.

Despite these differences with other primates, humans of lower socioeconomic class have poorer health. This is not just due to poverty preventing access to health care. Countries with universal and equal access health care still show a pronounced socioeconomic health gradient.

Sapolsky has strong feelings about the lack of social equality among humans and its effect on the health of the poor. He says, "It is a testimony to the power of humans, after inventing material technology and the unequal distribution of its spoils, to corrosively subordinate its have-nots."

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