An Unknown Unknown - What's the State of Microbial Biodiversity? Scientists have shown that healthier communities of microorganisms in the human gut are also more diverse. But what about the natural world? We know that biodiversity among plants and animals is in serious decline and has been for some time. Some researchers have even warned that a sixth mass extinction is currently happening. Now, investigators are asking whether we should begin to monitor microbial diversity. Though we're aware of lots of mysteries, there's also stuff we're totally unaware of that we also haven't even thought about - the unknown unknowns. Microbial diversity is a kind of biological unknown unknown, said Dr. David S. Thaler of the University of Basel, Switzerland, a Guest Investigator at The Rockefeller University's Program for the Human Environment (PHE).