Although we don’t display social status the same way other primates do, many of the same physiological reactions apply. Having a low position in any primate hierarchy is associated with chronic stress and poor health. Researchers from the University of Chicago, Emory University, Johns Hopkins and the University of Vermont have found that the social status of female rhesus monkeys even affects gene expression. Correlations between gene expression and status have long been described, but efforts to prove causation have been problematic.
The scientists were able to control the social rank of the monkeys by manipulating the order in which new members were introduced into a small group. Blood tests revealed that certain genes were expressed at different levels, depending on the status of the monkey. For example, genes involved in immune reactions were expressed at a higher rate in high status females. In fact, when given blood samples, researchers were able to predict with 80% accuracy where a monkey fell within a hierarchy of five group mates. This was true even when the same unfortunate females were moved from group to group, changing status position each time. In other words, gene expression can change from moment to moment depending on where the individual finds herself ranked among her peers.
These data indicate that it is rank that influences gene expression and not the other way around. If gene expression came first, monkeys would not necessarily change status upon being introduced into a new group. Because socioeconomic status in humans is also associated with differences in gene expression, there’s every reason to think that similar effects apply to us.