Key Study: Social status and stress in Olive Baboons (Sapolsky, 1990)

Travis Dixon Health Psychology, Key Studies, Studies and Theories Leave a Comment

Sapolsky's classic 1990 study on African Olive Baboons helps give us an insight into the links between social status as an explanation for chronic stress.
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An interesting finding in the field of stress and health psychology is that people with higher social status are generally in better health: they have lower rates of heart disease, are less obese and live longer. Why? One reason could be because they are less stressed. 

A lot of our knowledge about stress and health comes from animal studies, particularly those on non-human primates (e.g. monkeys and baboons). Robert Sapolsky is one of the preeminent psychologists in the field of stress in primates he’s spent years studying social hierarchies in primate species. In particular, he has studied how social rank correlates with stress, stress hormones and health.  We’ll look at some of this research in this blog post.

Olive Baboons (like these two babies) make for good animal models of human social hierarchies and their links with stress.

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But researchers didn’t always agree on this. In the 1950s psychologists believed that it was the high-powered and high-status individuals who had the highest stress levels. It was believed they suffered from what they called the “executive stress syndrome.” But by the 1960s this research was discredited and it was then believed that subordinate (lower ranking) individuals had higher stress (Sapolsky, 2005).

This article is written with material adapted from our “Stress” unit for Health Psychology.

An important study in the field of stress and its link with status was conducted by Sapolsky in 1990. In this classic study, Sapolsky observed a troop of Olive Baboons in the Serengeti plains of Africa for 12 years. Data was collected every year with the aim of understanding how social rank was correlated with stress levels.

These particular baboons in the Serengeti make excellent animal models of human societies because they live long lives in large social groups (of about 50-200 baboons in a troop) and they are very intelligent. They also live in an environment abundant with food and they’re large, so they don’t have to worry about predators. This means they have no immediate threats and have all the time in the world to create complex social hierarchies and the social stressors that go with it – much like our own modern societies.

Social rank and stress in baboons  (Sapolsky, 1990)

One aim of this study was to see how rank is associated with stress.

Olive baboons are social animals with clearly defined hierarchies, like humans. (Credit: Stolz Gary M, USFWS, pixnio.com)

Methods:

  • 12-year longitudinal study.
  • Observational data was gathered to learn the social ranks and behaviours of the baboons. Data was also gathered on their personality traits.
  • Blood samples were gathered using blowguns to tranquilize the baboons and measure their stress levels by analyzing cortisol levels in the blood (i.e. cortisol levels are the measurement of stress).
    • To control for extraneous variables affecting the blood samples, the animals would be tranquilized by shooting them with darts from a blowgun. To avoid confounding factors influencing the blood sample, the samples were taken at the same time of day because our circadian rhythm (body clock) alters our levels of hormones throughout the day (cortisol levels tend to peak in the morning and are lowest in the evenings). They were not taken immediately after sex, a fight, or during illness. The animals were shot with the dart while they were relaxed and not expecting it.

Results:

  • One finding from the study was that the subordinate, lower ranking males were hypercortisolemic – they had elevated levels of cortisol in their blood. This is because they experienced more stressors. High-ranking baboons tended to have lower levels of cortisol.
  • In one year (1981), 6 males formed an alliance to remove the highest ranking male. They succeeded, but then all six fought with each other to get the top spot. During this tumultuous time of instability in the troop, these dominant males’ cortisol concentrations were as high as subordinates.

This graph of the high rank (black) and low rank (white) baboon’s cortisol levels shows that rank is linked with stress, but other factors are also important to consider. (I do not know why the data is missing from 1981).

  • In 1984 there was a massive drought in the Serengeti and food became scarce While their body weight stayed the same and they managed to survive the drought, the baboons had to work much harder to find food and stay alive. This led to a 78% reduction in aggression. Not surprisingly, it also led to drops in cortisol levels of the subordinate males. The high-ranking males still had lower levels (slightly), but the difference between the two groups was the smallest over the 6 years of study.
  • There were five traits that were important. If a dominant male had any of these traits, they would have lower levels of cortisol. However, if he had none then his cortisol levels would be as high as subordinates. Also, the difference between cortisol levels between dominant and subordinate males is smaller than is the difference between two dominant males with differences in these behavioural traits. They were:
    1. Social support: Having lots of interactions with infants and nonsexual interactions with females helps to reduce stress.
    2. Displaced aggression: If a baboon is able to displace aggression onto someone else after losing a fight (e.g. picking on someone smaller) they will have lower stress levels.
    3. Ability to detect threat: Knowing when a rival was acting passively or threateningly – the ability to make an accurate judgement if a rival was passive or about to be threatening helps reduce stress.
    4. Asserting control: If a rival was posing a threat, being able to control the situation by starting the fight (and these males won more of these fights than they lost) helps to reduce stress.
    5. Knowing when you’re beaten: Understanding when a fight had been won or lost helps to reduce stress – this can be judged by an observer based on the behaviour of the baboon after a fight with a rival.

Conclusions and Applications:

  • Social rank is associated with stress – lower ranking males have higher stress levels than higher ranking males.
  • But it’s not simply a matter of high rank = low stress. Personality traits and environmental factors are important influences as well.

Critical Thinking Considerations

  • How can these results show that social rank is not the only explanation for chronic stress?
  • How is field research like this better (or worse) than using animals in a laboratory? Are there any ethical concerns with studying animals in this way?
  • Sapolsky’s early research (including this study) focused on males and social hierarchy in males. How can that influence the generalizability of these results? What specific reasons are there to suspect the same results might not apply for females?

References

  • Abbott DH, et al. Are subordinates always stressed? A comparative analysis of rank differences in cortisol levels among primates. Horm Behav. 2003 Jan;43(1):67-82. PMID: 12614636.
  • Sapolsky, R. M. (1990). Adrenocortical function, social rank, and personality among wild baboons. Biological Psychiatry, 28(10), 862–878. https://doi.org/10.1016/0006-3223(90)90568-M
  • Sapolsky RM. The influence of social hierarchy on primate health. Science. 2005 Apr 29;308(5722):648-52. PMID: 15860617.
  • Stringhini, Silvia et al. “Socioeconomic status and the 25 × 25 risk factors as determinants of premature mortality: a multicohort study and meta-analysis of 1·7 million men and women.” Lancet (London, England) vol. 389,10075 (2017): 1229-1237.

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