In 2011, Dunn and his colleagues collected samples from more than 500 volunteers at the 2011 Science Online conference in Raleigh, North Carolina, and at the Darwin Day event at Raleigh's Museum of Natural Sciences. But the researchers weren't all that interested in the lint. Instead, they wanted to understand the belly button microbiome. "The belly button is one of the habitats closest to us, and yet it remains relatively unexplored," they wrote. So they set out to find out what bacteria live inside of our navels.

Beginning with that initial study (there has since been a second round of sampling), Dunn and his team have discovered tremendous microbiological diversity hiding in belly buttons, a veritable treasure trove of microscopic lifeforms.

Navel adaptation



In the 60 samples they first assessed, they counted at least 2,368 species and suspect that figure is likely an underestimate. To put that into context, that's more than twice the biodiversity of North American birds or ants. But most of those species were rare: 2,128 of them were present in the navels of fewer than six people. In fact, most were only seen on a single individual. Despite the staggering diversity, the vast majority of bacteria found in human navels come from but a handful of species. While there was no one species common to every individual, eight species were present on at least 70% of participants. Together, those eight species accounted for almost half of all bacteria found.

The researchers also found three species of archaea, a type typically found only in extreme environments. Interestingly, two of the three came from a single individual who said he hadn't taken a shower or bath for several years.