Why would scientists re-create the black plague?

A team of German, Canadian, and U.S. scientists have reconstructed the genetic sequence of one of history's worst plagues. The Black Death swept through Europe between 1347 and 1351, killing 30 million to 50 million people — up to half of Europe's population at the time. The plague "was literally like the four horseman of the apocalypse that rained on Europe," says Johannes Krause of Germany's University of Tubingen, lead author of the study published in Nature. "People literally thought it was the end of the world." Why try to bring it back to life? Here's what you should know:

How did scientists re-create the bacterium's DNA?

Study co-author Kirsten Bos, of Canada's McMaster University, extracted dried blood from the teeth of four 14th-century plague victims exhumed from a London graveyard located under today's Royal Mint. The 660-year-old plague DNA was in bad shape, fractured and mixed with human DNA and other bacteria. But using new techniques and modern disease strains to attract the ancient plague DNA, researchers were able to separate, clean, and sequence the black plague. This "technical tour de force" will be used as a model to re-create the pathogens that caused other ancient epidemics.

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Why would you ever resurrect such a deadly bug?

Partly to settle a scientific debate between those who argued that modern strains of the plague bacterium, Yersinia pestis, descended from the original variant that caused the Black Death, and those who said a different bug caused the medieval plagues. This study proves the former group right: The 14th century version of Y. pestis is nearly identical to the less-virulent strains that exist today. "It's the grandmother of all plagues that's around today," says Krause. Studying the original will likely help scientists understand modern-day infectious disease.

Could this spark another Black Death?

No. Even if a resurrected version of this deadly bug escaped the ultra-secure lab, we'd be okay. Today's world is a very different than medieval Europe, and leaps in public health and better living conditions would blunt the disease's spread. And antibiotics would surely snuff it out.

Sources: AP, BBC News, Bloomberg, New York Times, Reuters, TIME