Rob Dunn cultured the bacteria of people’s belly buttons:
One can imagine many factors that influence which bacteria are on your skin; whether you were born c-section or vaginally, gender, age, weight, whether you are an innie or an outie, whether you live in a city or the country, what climate you live in, whether or not you have a dog, and maybe even where you grew up or where your mother lived when she was pregnant with you. As we looked at belly buttons we saw a terrible, yawning, richness of life.
Philippa Warr describes the findings:
The Belly Button Biodiversity Project, which explores the bacterial ecosystems living in its participants' navels, has discovered that a small number of bacterial phylotypes (or "species") dominate the micro-landscape. The biologists' results show a "jungle of microbial diversity" with over 2,300 species of bacteria present and only eight of those recurring frequently — a similar diversity distribution to that of tree species in tropical rainforests.
Carl Zimmer's analysis:
It’s possible that the rare microbes are only visitors, dropping by for a short stay in our navels before dying out or traveling on. The most common species the scientists found may have long-term leases, having evolved adaptation that help them thrive in the bellybutton’s distinctive habitat. Dunn and his colleagues found that these abundant species were also closely related to each other compared to the rarer ones. It’s a pattern similar to the one found in rain forests, were only a few lineages of trees dominate, with many species only contributing a few trees. Your belly button, in other words, really is a jungle.