Chimpanzees famously throw their feces and even eat their own poop from time to time. But scientists have also found that they’re not into other chimps’ poop, exhibiting a disgust response similar to humans. Scientists have long been fascinated by our similarities and differences with our primate cousins, and new research on chimpanzees’ beds shows a subtle way in which chimps may actually have better hygiene than we do.

In a paper published Wednesday in the journal Royal Society Open Science, a team of researchers collected samples of bacteria and arthropods — insects, spiders, crustaceans — from chimpanzee beds in the Issa Valley in Tanzania and compared their tiny inhabitants to the surrounding forest. They found that the chimpanzees’ beds have pretty similar biological communities those in the rest of their environment, which means their beds don’t actually show much evidence of chimpanzees ever inhabiting them. This is a stark contrast to human beds, which show ample evidence of human inhabitance, including fecal bacteria. There’s a couple of reasons this may be the case, and they’re both linked to civilization.

Chimp's Nest
Chimpanzees don't usually sleep in the same bed more than once.

First of all, human homes do a pretty good job of cultivating a specific set of microbes, specifically the ones that come from our bodies. By closing our living space off from the rest of our local environment, we ensure that the microbes and bugs from outside won’t really make their homes inside. Second, and maybe a little less obvious, is the fact that chimps don’t sleep in the same place every night, which lessens their bacterial impact on their beds. They even poop off the side of their beds, lessening their fecal fingerprint. Humans, on the other hand, leave a huge microbial footprint in their beds by sleeping and shedding in the same sheets night after night, often without washing them.

Despite these differences between the bedding habits of humans and chimps, the researchers were still a bit surprised at their results. “We expected to see a lot of ectoparasites and a lot of fecal bacteria, because there’s been a lot of evidence showing that fecal bacteria builds up in the fur of chimpanzees,” Megan Thoemmes, a Ph.D. student of evolutionary history at North Carolina State University and the first author on the paper, told National Geographic.

Scientists have recently suspected that, as humans cut ourselves off from the environment, we alter our ability to respond to pathogens, something known as the “Hygiene Hypothesis. But what they don’t know much about is how this type of behavior shows up across species. This recent study represents an attempt to fill in that gap in the scientific literature.

The study’s authors write that sometime between 20,000 and 1 million years ago, our ancestors likely began sleeping differently from what we observe in chimps, which led to how we live today. “With that change, the proportion of time we spend with these species has continued to increase, as we now spend the majority of our lives indoors,” they write. And with that indoor time, we have created indoor environments that bear the clear biological marks of our indoor lives.