News from the showerhead biome is just one part of this fact-filled, occasionally disgusting, slightly alarming book. Dunn has been involved in an obsessive quest to document the tiny inhabitants of indoor environments, a project that involves teams of professional and amateur bug-watchers to take samples not only from showerheads but from door frames, refrigerators, hot water heaters, cellars, toilets, pillowcases, all sorts of surfaces from the places we call home. These workers swab and seal, swab and seal, and send their thousands of samples to Dunn’s lab in Raleigh, or to his other lab at the Natural History Museum of Denmark, for an ongoing microbial census.
“We expected to find a few hundred species,” Dunn writes of his first foray into indoor microbe-hunting, which involved 1,000 homes from around the world. Instead, he and his colleagues found a “floating, leaping, crawling circus of thousands of species,” perhaps as many as 200,000, many of them previously unknown to science.
These denizens of interior spaces are our most frequent companions. In the industrialized world, we spend upward of 90 percent of our time indoors. Luckily, most of our co-habitators are either benign or actually beneficial in some way, like the house spiders that keep down indoor populations of flies or mosquitoes that can carry disease. But because we’ve become so hyper about making our surroundings as pristine as possible — sealing off our homes from the outdoors and using pesticides and antimicrobials with a vengeance — we’ve tipped the scales away from those harmless or helpful bugs, in favor of some of the bad guys.
According to Dunn, indoor microbes are among the fastest-evolving species on the planet; they have an uncanny ability to live in ecological niches you could hardly imagine existing, like the dead skin cells we slough off every day (which is all that’s needed to survive for a class of bacteria known as detritivores). They manage to evade our assaults, and evolve their way out of just about every biocide we throw at them. We’re left to contend with the consequences of our own warfare, such as pesticide-resistant German cockroaches and bedbugs, and antibiotic-resistant MRSA bacteria. We have turned a relatively harmless indoor biome into something that can make us sick.
That’s the take-home message of “Never Home Alone,” that the richer the biodiversity in our indoor environment, the better. “The biodiversity of plants and soil can help our immune systems function properly,” Dunn writes. “The biodiversity in our water systems can help keep pathogens in the water in check. … The biodiversity of spiders, parasitoid wasps and centipedes can help control pests. The biodiversity in our houses provides the opportunity, too, for the discovery of enzymes, genes and species useful to all of us, whether to make new kinds of beers or to transform waste into energy.”