Why would you want to stress a monkey? Hopefully you don’t. But learning about stressed monkeys can help us explain stress problems in humans.
I’m using the word “monkey” in this article for simplicity’s sake. However, the correct term is “non-human primate” as this includes the range of species that are studied. e.g. Abbott et al. reviewed studies on baboons as well as marmoset, tamarin, rhesus, cynomolgus, talapoin and squirrel monkeys.
Decades of animal research has shown that social status is connected with stress. Typically speaking, monkeys with a higher rank in their group are less stressed and have lower levels of stress hormones like cortisol. Low-ranking monkeys, on the other hand, have higher rates of stress. This link between low status and high stress has also been found in human studies (e.g. the Whitehall studies in the UK). This finding contradicted the earlier belief (from the 1960s) that those with high rank and high-power positions were more stressed. Therefore, one explanation of chronic stress (a major health problem) is that it’s caused by our social status.
However, the current view is a little more complicated – a monkey’s status is only linked with stress if it increases their exposure to stressors. Similarly, loads of studies on monkeys (and baboons) have found there are multiple factors that influence the relationship between social status and stress. Three common factors are:
- High rates of being subjected to stressors,
- Low availability of social support,
- Minimal presence of kin (family).
This means a low ranking monkey is only more stressed than others if: it has lots of stressors, less social and family support. This means a low-ranking monkey could have less stress than a higher ranking monkey if his low rank reduces his exposure to stressors. For example, a low-ranking tamarin monkey who has a lot of friends and no bullies, might experience less stress than the alpha of the troop who has to continually fight against possible challengers to his title of alpha status.
There was too much fascinating research to include everything in our new unit on Stress for the Health Psychology option, so this is some extra material if you’re interested.
Evidence from this comes from a study by Abbott and colleagues (including Robert Sapolsky) in 2003. They conducted an “informal meta-analysis” by comparing the levels of cortisol across seven species of nonhuman primates (including baboons and rhesus monkeys). Their results support the fact that the subordinate monkeys had higher rates of cortisol only if they were exposed to more stressors, had fewer chances to get “support” from other primates (e.g. through social grooming) and if they were not near members of their family. Therefore, social and family support can reduce the effects of status on the stress response and status is linked with stress because of its relationship with exposure to stressors.
Is this low-ranking Tamarin monkeyed stressed? Maybe, but it would depend on 10 important factors like their personality and the characteristics of their troop. (source: wikicommons).
In fact, Sapolsky (2005) outlines ten factors that affect whether or not status is linked to stress:
- Resource inequity: In societies with more equality, subordinate males have less stress.
- Maintenance of dominance: If a high ranking individual has to fight and keep their status through aggression and competition, they will have higher stress than subordinates.
- Breeding style: Monkey species are generally either cooperative or competitive breeders. In competitive breeding troops, one male dominates (the alpha) has mates with all the females and maintains this privilege through dominance and aggression. In these societies, low ranking monkeys have high stress. But in cooperative breeding groups, there is one female who dominates breeding (because she is ovulating) but this is done in a less hostile and aggressive way. Other females help to raise the young and wait their turn to breed. In these societies, low ranking monkeys have low stress levels.
- Stability of social ranks: Societies with more stable ranks, especially hereditary titles, are worse for subordinate (low ranking) monkeys. This was seen in Sapolsky’s classic 1990 study of the Olive Baboons in Africa when 6 subordinates plotted to overthrow the alpha. It worked but then they fought for a long time between themselves trying to gain that top spot – their stress levels were as high as lower ranking baboons.
- Subordinate coping strategies: Low ranking monkeys that use strategies like grooming others, having friends around, displacing aggression (taking their anger out on someone smaller than them) can help reduce stress in monkeys.
- Subordinate avoidance of dominants: How easily can the monkey avoid dominant individuals? The harder this is the more stressed they’ll be. In monkey troops where this is easy to avoid, they have lower stress.
- Subordinates use of alternative strategies: If a subordinate can someone remove themselves from the hierarchy, they might have lower stress. For example, they might use a different approaches to finding a mate rather than challenging the alpha, such as reciprocal grooming. If they can do this, the lower ranked monkey will be less stressed than normal.
- Stress of dominating mating: Some monkeys have short mating seasons and competition for mates is fierce. In these societies, high ranking monkeys have higher stress.
- Atmosphere and culture: Believe it or not, some primate groups can have different cultures and this can be passed on through generations. One baboon group studied by Sapolsky is uncharacteristically non-violent. These subordinate males do not have similar stress profiles as in other groups.
- Personality: Individual monkeys who have a lack of social outlets and are bad at finding social support (e.g. no reciprocal grooming or can’t pick on someone smaller) might have higher stress. Similarly, some monkeys are more “jumpy” than others – they have a hard time distinguishing between a threatening and non-threatening stimuli. For example, they can’t tell if the alpha is about to come over and ask to be groomed or to grab their tail and chase them away. These monkeys are more stressed. In humans, they’d probably have what we call high trait-anxiety.
You might notice that the list confirms the logical and rather inescapable truth about stress: the more stressors you are exposed to, the more you will be stressed. Therefore, your social rank will only influence your stress levels if it affects your exposure to stressors. This is an important consideration when it comes to explaining health problems like chronic stress by looking at factors such as social rank.
Some students have noticed that monkeys and other non-human primates appear a lot in my resources. There’s no reason for this other than I think they’re really cool. In this case, I’m writing about monkeys because they’ve been very important in the field of stress research in psychology.
Critical Thinking Considerations: Can we apply this to humans?
Human studies have shown similar findings – social status is linked with health. For instance, people in lower socioeconomic groups (e.g. poor people) are more at risk for a number of health problems, including heart diseases and obesity. Across the globe we also have thousands of different cultural and social systems. Do you think Sapolsky’s summary above suggests that the link between social rank and stress in monkeys will be more similar or more different in humans. Why?
References:
Abbott DH, Keverne EB, Bercovitch FB, Shively CA, Mendoza SP, Saltzman W, Snowdon CT, Ziegler TE, Banjevic M, Garland T Jr, Sapolsky RM. Are subordinates always stressed? A comparative analysis of rank differences in cortisol levels among primates. Horm Behav. 2003 Jan;43(1):67-82. Link
Travis Dixon is an IB Psychology teacher, author, workshop leader, examiner and IA moderator.