The Necrobiome Is for the Dead What the Microbiome Is for the Living

Millions of bacteria live inside your gut. Your microbiome, as it's called, can tell scientists a lot about you. A corpse has its own colony of bacteria, and forensic scientists can use it to determine when the person died. Welcome to the necrobiome.

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Night of the Living Dead

Most natural processes follow predictable steps. A seed germinates, grows into a flower, spreads its pollen, and produces more flowers. A human embryo has such predictable development that a doctor can roughly determine its age just by looking at it with an ultrasound. The same goes for death. Whether it's a worm or whale, once its life is extinguished, a predictable march of scavenging insects and microbes comes along to feast on the remains and return it to the earth.

That predictability is incredibly useful when calculating the time of death is your job. Although forensic scientists may often make this assessment using factors like the stage of decomposition (a skeleton is much farther along than a fully intact corpse, for instance) or scavenging insects (have the eggs had time to turn into larvae?), those measures aren't always dependable. A corpse rots faster in the summer heat than it does in the winter snow, and insect species come and go with the seasons. But bacteria? They're always in the soil, waiting for a nutritious feast to come along above ground.

The Clock Is Ticking

The area of microbial forensics is fairly new, but that means a lot has been discovered in a short amount of time. In 2013, researchers led by Jessica Metcalf of the University of Colorado, Boulder figured out that the necrobiome of decaying mice could tell them the animal's time of death to within three days over a nearly two-month period. In 2016, the same researchers figured out that the habitat didn't matter: Whether in desert, prairie, or forest, the same type of microbes follow the same predictable processes, and that lets scientists use them to judge the time of death no matter the location.

Also, no matter the species. Because the bacteria that colonize corpses come from the soil, not the corpses themselves, scientists could potentially use the discoveries they make about mouse corpses to tell them how long a human has been dead. But that's just mouse studies — there are researchers working on real human cadavers, too.

Some people donate their bodies to decompose on body farms, where forensic scientists study what happens to corpses over time. In 2016, researchers from the City University of New York used DNA from bacteria they found in some of these cadavers and used machine learning to create a model that could predict the time of death to within roughly two days. There's still a lot to learn about how elements like weather, health, drugs, and other variables affect the way a body decomposes, but whatever the results, the necrobiome will surely play a big role.

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Want to learn more about dead bodies? You've got to read "Stiff" by Mary Roach, one of our very favorite science writers. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Ashley Hamer October 17, 2017

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