A researcher investigating how the stress levels of people in non-industrialized societies differ from those of modern Americans found himself in a different kind of stressful situation when he came face-to-face with a killer.

Biological anthropologist Samuel Urlacher left the urban jungle of Boston, where he was a graduate student at Harvard University, for the actual jungle of Papua New Guinea. Since 2013, he’s worked among the Garisakang, an isolated clan of about 500 foragers and garden-scale farmers living in tropical villages without electricity or running water. Urlacher, now a postdoctoral fellow at Hunter College in New York, has collected more than 1,600 saliva samples in order to measure the stress hormone cortisol.