A big topic of conversation in zoos and other animal facilities is stress: Who suffers from it? What are the causes and repercussions? How can we identify it biologically? And what are the best ways to recognize the causes in hopes of alleviating the stress?

We have all seen stress in animals (including ourselves) appear in some form of aberrant behaviors and other various conditions: pacing, head tossing (with carnivores), hypergrooming, displaying (like throwing feces or vomit), losing sleep, breaking out into hives, and self mutilation, just to name a few. While these behaviors and conditions are visual, concern also lies in what we can’t easily see… chronic stress resulting in suppression of the immune system, high blood pressure, stress dwarfism, fibrosing cardiomyopathy, etc.

Robert Sapolsky of Stanford University has been researching the physiological effects of stress on health (with a nice set of publications including both scientific papers and popular books) for decades and recently presented at the American Association for the Advancement of Science in San Francisco on Feb 17th, 2006 (which I’m sad to say I missed). ScienceDaily highlights his research asking “Why Do Humans And Primates Get More Stress-related Diseases Than Other Animals?

The bottom line is that:

“Primates are super smart and organized just enough to devote their free time to being miserable to each other and stressing each other out. But if you get chronically, psychosocially stressed, you’re going to compromise your health. So, essentially, we’ve evolved to be smart enough to make ourselves sick.”

Sapolsky helps us to think of it in terms of real stress versus psychological stress:

“During real stress – for example, something is intent on eating you and you’re running for your life – versus what your body does when you’re turning on the same stress response for months on end for purely psychosocial reasons.”

By constantly stressing ourselves out we are forcing our bodies to run in ways that are only intended for short bursts of time. We are essentially breaking down our system and becoming vulnerable to severe health problems (like those previously mentioned).

The baboon studies Sapolsky spearheaded are hugely relevant to this situation:

“We’ve found that baboons have diseases that other social mammals generally don’t have. If you’re a gazelle, you don’t have a very complex emotional life, despite being a social species. But primates are just smart enough that they can think their bodies into working differently. It’s not until you get to primates that you get things that look like depression.

The reason baboons are such good models is, like us, they don’t have real stressors. If you live in a baboon troop in the Serengeti, you only have to work three hours a day for your calories, and predators don’t mess with you much. What that means is you’ve got nine hours of free time every day to devote to generating psychological stress toward other animals in your troop. So the baboon is a wonderful model for living well enough and long enough to pay the price for all the social-stressor nonsense that they create for each other. They’re just like us: They’re not getting done in by predators and famines, they’re getting done in by each other.”

Needless to say, it’s important to understand more of the neuroscience behind stress. Sapolsky highlights some of the new research:

“It’s becoming clear that in the hippocampus, the part of the brain most susceptible to stress hormones, you see atrophy in people with post-traumatic stress disorder and major depression. There’s a ton of very exciting, very contentious work as to whether stress is causing that part of the brain to atrophy, and if so, is it reversible. Or does having a small hippocampus make you more vulnerable to stress-related traumas?”


“There are now studies showing that chromosomal DNA aging accelerates in young, healthy humans who experience something incredibly psychologically stressful. That’s a huge finding.”

Animals respond differently to every situation and stress is no exception. Understanding these differences, according to Sapolsky, is one of the most important areas of neuroscience research:

“This gets you into the realm of why do some people see stressors that other people don’t, and why, in the face of something that is undeniably a stressor to everybody, do some people do so much worse than others?”

It will be interesting to see how this research unfolds. Will it result in solid methods to understand how stress works? Will it lead to non-invasive biological markers of stress? Currently some researchers are relying on cortisol as a hormonal marker of stress. I’ve been to many a lecture reviewing the pros and cons of using cortisol in behavioral research, each generally ending with the same thought: cortisol is an accurate marker telling us that something is happening, but whether that something is bad stress (versus good stress, like riding a roller coaster) is still unknown. Some may say that the captive situations we’re using in research are more likely to prompt bad stress which would mean that cortisol is a better marker of bad stress than we are giving it credit for, but until that separation is apparent, we’re kind of back to the drawing board.

Understanding the animals that we work with can sometimes be a challenging job. Hopefully with all of the research going on in this field, we will be able to formulate a better understanding of what stress is (for each individual animal) so that we can do our best to identify and eliminate the stressors (and consequently the health problems).