Imagine studying animals without seeing them. Does that sound ludicrous? To people like us, who first got interested in biology because we love animals and enjoy studying them, yes, it sounds like a poor deal. Yet, if you think about what forensic investigators do when they seek DNA evidence at a crime scene, or what doctors do when they detect a pathogen in a patient’s blood, it is exactly that: they detect life forms without seeing them.
DNA is life’s blue print. It is present in virtually every organism on Earth, and we usually study it by extracting it from a piece of tissue or a blood sample. But DNA, really, is everywhere: animals shed it constantly, when they scratch themselves, when they release urine, eggs, saliva, excrement and, of course, when they die. Every environment, from your bed to the deepest recesses of the oceans, is full of “biological dust”, mostly cellular material, which contains the DNA of the organisms that left it behind. This, we call “environmental DNA,” or eDNA.
Assisted by increasingly fast, accurate and affordable technology, scientists have begun, in recent years, to sequence this trace DNA from many environments. And this “micro” approach has even proved to be useful to scientists investigating environments as vast as the oceans.