By Ed Yong

Last year, the world learned that researchers led by David Evans from the University of Alberta had resurrected a virus called horsepox. The virus hasn’t been seen in nature for decades, but Evans’s team assembled it using genetic material they ordered from a company that synthesizes DNA.  

The work caused a huge stir. Horsepox is harmless to people, but its close cousin, smallpox, killed hundreds of millions before being eradicated in 1980. Only two stocks of smallpox remain, one held by Russia and the other by the United States. But Evans’s critics argued that his work makes it easier for others to re-create smallpox themselves, and, whether through accident or malice, release it. That would be horrific: few people today are immunized against smallpox, and vaccine reserves are limited. Several concerned parties wrote letters urging scientific journals not to publish the paper that described the work, but PLOS One did so in January.