New research shows that humans have been transforming the earth and its ecosystems for millenniums — far longer than previously believed. These findings call into question our notions about what is unspoiled nature and what should be preserved.

Are there any pristine ecosystems out there? The evidence is growing that our ideas about virgin nature are often faulty. In fact, the lush rainforest or wind-blown moorland we think is natural may be a human creation, with alien creatures from distant lands living beside native species. Realizing this will change our ideas about how ecosystems work and how we should do conservation.

We like to think that most nature was pristine and largely untouched until recent times. But two major studies in recent weeks say we are deluded. In one, Erle Ellis, a geographer at the University of Maryland Baltimore County, and colleagues have calculated that at least a fifth of the land across most of the world had been transformed by humans as early as 5,000 years ago — a proportion that past studies of historical land use had assumed was only reached in the past 100 years or so.