Despite the popular belief that the Black Death was an indiscriminate killer, analysis of skeletons taken from a London cemetery for Black Death victims prove otherwise. This according to anthropologist Sharon DeWitte of the University of Albany in New York.

DeWitte, along with Pennsylvania State University anthropologist James Wood, found that the pandemic was still somewhat selective. Some experts believe that it killed people regardless of age, sex, or level of health, but DeWitte and Wood found that people already in poor health were still more likely to die.

While unhealthy people are often more vulnerable in the face of epidemics, DeWitte noted that "there's been a tradition of thinking that the Black Death was this unique case where no one was safe and if you were exposed to the disease that was it. You had three to five days, and then you were dead."

The cause of the Black Death, which killed about 75 million people in Europe and elsewhere during the 14th century, is still something of a mystery. Many experts believe that it was caused by Yersinia pestis, a bacterial disease spread by rat fleas, while others think that it was caused by a viral hemorrhagic fever similar to that caused by the Ebola virus.