Greg Dwyer is a mathematical ecologist, based at the University of Chicago, who studies outbreak populations of forest insects.  His work involves trying to understand the extreme boom-and-bust cycles of species such as the gypsy moth (Lymantria dispar), which explodes occasionally into huge infestations, defoliates trees throughout a region, and then suddenly crashes.  After a period of years at low population, another gypsy moth outbreak begins, the numbers increase suddenly and grotesquely, the infestation peaks for a year or two—and then comes another crash.  The main factor driving the crash phase of the cycle is viral infection, killing gypsy moths like a medieval plague.  That's why I recently went to see Dwyer at his office on the UC campus.  I thought his research and his ideas might help inform the final chapter of my book in progress, which concerns the ecology and evolution of scary viruses—the ones that kill humans, not gypsy moths.  The book will appear next year, under the title Spillover. 

Dwyer is a rare combination: a highly sophisticated math guy who creates mathematical models of ecological processes, and a field man who still goes into the forest, collecting his own data.  He also runs a lab, in which he and his grad students and postdocs can watch the moth-virus interaction in its excruciating stages.  The virus in question is called nucleopolyhedrovirus (NPV).  There's a whole group of NPVs, some infecting such other forest insects as the Douglas-fir tussock moth and the Western tent caterpillar.   This one is specifically adapted to kill gypsy moths.  It consumes them from within, it dissolves them, it virtually melts them down—the way Ebola virus supposedly (but not in reality, only in the pop literature of Ebola hype) melts a human body.  For a gypsy moth, it's no hype.  "They pick up the virus," Dwyer told me, "they go splat on a leaf."

Then he showed me.  In the basement of the biology building, he unlocked a door to what he called "the dirty room" of his lab complex and invited me in.  From an incubator, one of his postdocs pulled out a plastic container of gypsy moth caterpillars, which had been thriving and growing on a medium of caterpillar chow until, two weeks earlier, they were artificially infected with NPV.  Splat.

During our chat in his office, I had questioned Dwyer about what I call The Analogy: Does our human population on Earth, now standing at 7 billion, resemble an outbreak population of forest insects?  If so, should we expect that a pathogen as lethal and hungry as NPV will come along, sooner or later, and knock us back down to size?  Dwyer is a careful scientist, rigorous but thoughtful.  He considered the question.   He drew graphs on a whiteboard.  He paused, then considered the question again.  He gave me a complicated, valuable answer, to which I'll try to do justice in the last chapter of my book.