Forests became less diverse when ancient people started herding pigs.

Ancient DNA extracted from layers of sediment in a Czech forest shows how a drop in biodiversity coincided with a shift to pig herding about 4000 years ago.

Ancient DNA unearthed from a European rock shelter suggests that local herders tended goats and sheep more than 5000 years ago, but switched to primarily pigs 2000 years later – right about when the surrounding forests became much less biodiverse.

Although further research is needed, the findings hint that keeping pigs – which root the ground and are far less picky eaters than goats and sheep – might have played a role in how modern forests took shape. The discovery provides strong evidence that analyzing ancient sedimentary DNA can...