Some of the most memorable, appalling statistics in history are those of the accidental genocides wrought by human exploration. After its introduction to Central America by the conquistadors in 1520, for example, smallpox had by 1527 killed millions in Mexico and precipitated the collapse of the Inca empire. The same disease, introduced by Europeans to north America, killed 90% of the Massachusetts Bay Indians between 1617 and 1619. By the end of the 18th century, European diseases—of which smallpox was the worst—had managed to kill 90-95% of the native population of the Americas (Roy Foster gives a brief, haunting account of this process in the first section of his masterpiece, The Greatest Benefit to Mankind).
In the 10th December edition of The New Yorker, there’s a piece by the writer Richard Preston, “A Death in the Forest,” that describes something alarmingly similar currently taking place in the plant kingdom. Preston focuses on the plight of the eastern hemlock, a tree native to north America, which is now threatened by the spread of an Asian insect known as the hemlock woolly adelgid. Just like humans, plants have evolved immune mechanisms that protect them from pests and infections; and, just like humans, plants are almost totally unprotected by these mechanisms against threats that are “exotic”—that come from distant places with which, until recently, they had no possibility of contact.
We’ve all heard about this kind of thing before, but the examples Preston produces—combined with the quality of his expert, restrained, appalled narrative—prove truly astonishing. Since 1904, the fungal disease chestnut blight has killed almost every American chestnut tree. Since the 1930s, the American elm has virtually disappeared thanks to an Asian fungus and a European be…