When I first met Groussin in late October 2024, he had just flown more than 20 hours from Kiel, Germany, to Asunción, Paraguay, for what would be the conservancy’s second South American expedition. Poyet, who was six months pregnant with their second child, had stayed behind. “Please,” he implored me. “Mathilde is the true hero of this story. She led most of the work for this trip, including all the preparations. The only reason I am here instead of her is that she’s at home, gestating our baby.”
Groussin and his team were planning to travel another 10 or so hours to the Cerro Itá Guazú Indigenous reservation near the Brazil-Paraguay border, where they would collect blood, saliva, feces and vaginal secretions from as many people as were willing. But just about all the equipment they would need for that work — the chemicals and containers, the highly specialized storage tank, the 1,000 or so test tubes that they had already labeled — was stuck in customs, owing to a paperwork glitch. It was unclear when or whether that glitch might be resolved, but with a year of planning and no small investment of time and money at stake, their Paraguayan collaborators were anxious. “We are possibly very screwed,” Walter J. Sandoval Espínola, a microbiologist at the National University of Asunción, said as the two scientists and a half-dozen of their juniors gathered in front of the whiteboard that dominated an entire wall of Sandoval Espínola’s laboratory.
Groussin seemed unfazed. “We’ll figure something out,” he said, shrugging. “We’ve definitely been through worse.” A few hours later, they had bought, borrowed or jury-rigged most of what they would need, including a portable liquid nitrogen tank, several hundred test tubes that they would now have to relabel and dozens of lidded plastic bowls into which their study participants could defecate. The bowls were store-bought and see-through and would therefore have to be lined with paper or foil.
“People tend to be bashful about their poop,” Groussin explained. “If the containers are transparent, they’ll be less likely to return with samples.” He had other, similar concerns, which he enumerated for the group, as the hour grew late and the sky turned purple through the window behind him. They would have to make sure that a woman’s consent was permission enough to take vaginal swabs (in some places the men had been known to protest). They would also have to get tribal leaders’ permission to dispose of the leftover feces. “It would be unsanitary to leave it behind,” he said. “But taking it can also be tricky, because in some villages we’ve been to, the elders have worried about us doing witchcraft.”
