SAN FRANCISCO—Being highly intelligent and social, humans suffer from more stress-related diseases than any other animal, worrying about family, health, jobs and even the future. The average beast, on the other hand, does not spend much time worrying about these things.

But baboons do stress out, according to research presented here Saturday at the annual meeting of the American Association for the Advancement of Science.

Why is that? The answer sheds light on human stress.

New worries

Just a century or so back, the primary threats to human life were pneumonia, tuberculosis, childbirth, the flu and the like.

Nowadays, relatively few people die from the flu; instead most humans die of ailments that are relatively new to our species, such as heart disease, cancer, diabetes and Alzheimer’s disease, said Robert Sapolsky, a Stanford University neuroscientist.

“These are all diseases that are either caused by or being worsened by stress,” said Sapolsky, who has written several books including "Why Zebras Don’t Get Ulcers" and "A Primate’s Memoir." He regularly visits Kenya to study baboons, primates with no predators that experience environmental and social stress sources like humans.

If you're stomach is ripped open ...

Sapolsky explained homeostasis, is a state in which an organism or group is in balance, meaning for example, that there is an ideal level of glucose in the blood stream and the body’s temperature is favorable.

A stressor is anything in the outside world that knocks an animal out of homeostatic balance.

“You’re a zebra, a lion has leapt out, ripped your stomach open and you still need to get out of there,” Sapolsky told a packed room. “This counts as being out of homeostatic balance. The stress response is what your body does to reestablish homeostasis. That’s all you need to know about the subject if you’re a zebra.”

In the case of humans, however, the definition is expanded.

Humans can anticipate that something unfavorable is about to happen to them and can have a stress response prior to the event, which could help them cope. On the other hand, if a person believes they are about to be knocked out of homeostatic balance, but they are really not and this belief continues, then they are dealing with chronic stress.

You’re being profoundly human in such a case, Sapolsky said. “Sit down a hippo and try to describe what’s up with the ozone layer and he’s going to have no idea what you’re talking about. We go exactly through that stress response as that zebra or lion, but we do it for chronic psychosocial reasons,” he said.

This condition among humans, Sapolsky said, evolved from dealing with short-term crises. “For 99 percent of the beasts on this planet, stress is about three minutes of screaming in terror after which it’s either over with or you’re over with. And we turn it on for 30-year mortgages,” he said.

Stress response

Stress, a stimulus that causes a physical or psychological reaction, causes the release of hormones, such as adrenaline and cortisol, in all vertebrates. These hormones evolved to help facilitate behaviors that help vertebrates survive when they were about to become dinner.

During times of stress, animals go to their fat cells and liver and take out sugar and dump it in their blood streams.

“You go to the bank and you empty out the savings account and you turn it into cash, Sapolsky said. “Next, you want to deliver this energy as fast as you can. You increase your heart rate, your blood pressure and your breathing rate, to get that glucose to your thigh muscles in two seconds instead of three and you’re that much more likely to survive.”

However, humans, also generate these responses in non-life threatening situations, he said. On a daily basis, humans could be worried about their jobs, missing deadlines and angering someone they love, among other things.

"If you turn on the stress response chronically for purely psychological reasons, you increase your risk of adult-onset diabetes and high blood pressure,” Sapolsky said.

“If you're chronically shutting down the digestive system, there's a bunch of gastrointestinal disorders you're more at risk for as well."

Baboon model

For 30 years, Sapolsky and his colleagues have been gathering behavioral and physiological field data—such as blood samples, tissue biopsies and electrocardiograms—on African baboons, close cousins of humans. They study stress and neuron degeneration in the lab.

Unhealthy baboons, Sapolsky found, similar to unhealthy humans, have elevated levels of stress hormones and their immune responses and reproductive system are compromised.

"We've found that baboons have diseases that other social mammals generally don't have," Sapolsky said. "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."

These baboons have served a good model for understanding human behavior.

"The reason baboons are such good models is, like us, they don't have real stressors," Sapolsky said.

"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," he explained. "They're just like us: They're not getting done in by predators and famines; they're getting done in by each other."

Unlike baboons, however, humans can find different ways of coping with psychosocial stress.

Coping mechanisms

"We are capable of social supports that no other primate can even dream of," Sapolsky said. "For example, I might say, 'This job, where I'm a lowly mailroom clerk, really doesn't matter. What really matters is that I'm the captain of my softball team or deacon of my church,' that sort of thing. It's not just somebody sitting here, grooming you with their own hands.”

Humans also have a strong networking and support system.

“We can actually feel comfort from the discovery that somebody on the other side of the planet is going through the same experience we are and feel, I'm not alone,” Sapolsky said. “We can even take comfort reading about a fictional character, and there's no primate out there that can feel better in life just by listening to Beethoven.”