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This is Scientific American's 60-Second Science. I'm Emily Schwing.

The world may have just come to understand the nature of disease epidemics over the last year,

but for more than two decades David Earn has been working on his own understanding of infectious

diseases and he's using math to explain it all. And I'm particularly interested in

patterns of epidemics that have occurred in the past. And see what we can understand about

disease spread in the past and hope to learn about disease spread in the future from that.

Earn is an applied mathematician at Ontario's McMaster University. His research explores

factors that contribute to how diseases spread among people. And he's become an expert in

tracking down the historic documents about long ago epidemics that still hold mathematical clues

we can learn from today. Key to all this is his team's knack for digital sleuthing.

Early on in his career, Earn recognized that he could uncover numbers of deaths and their causes

in Europe by sifting through piles of old records. They're called bills of mortality,

and he's found thousands of them. If we were to look over time at all of them, they were published

weekly over hundreds of years. We'd see a pattern and that would be potentially very enlightening.

Earn started looking for one such pattern in London during the 1660s. That's when a pestilence

...