“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.”
From the article: Robert Sapolsky discusses physiological effects of stress