Animal species that have evolved, and survived, in low-disturbance environments - with little interruption from glaciation, fires, hurricanes, or anthropogenic clearing - are more sensitive to modern forest fragmentation, report Matthew Betts and colleagues. Using information from more than 70 worldwide datasets, they show that the proportion of forest species sensitive to fragmentation was nearly three times higher in forest ecosystems with low rates of historical disturbance. Their results help to inform why the biological effects of forest fragmentation are so variable among species and places. Habitat loss is the primary driver of biodiversity decline worldwide, most scientists agree, but how habitat fragmentation influences species diversity has been a source of debate for decades. The "extinction filter" hypothesis predicts that species that have evolved in high-disturbance environments should be more likely to persist in the face of new disturbances, like logging or forest clearing. Betts and colleagues sought to test this hypothesis for global forests using global datasets representing over 4,400 species. For each global study site, they assembled previously available data on forest fire severity, whether or not its location was glaciated in the last glacial maximum, whether or not it experienced tropical storms, and if historical anthropogenic forest loss exceeded 50%. Across all species combined, the authors found strong support for the extinction filter hypothesis. This result was particularly strong for arthropods and birds, the authors say. "Our results partly reconcile the debate about the conservation importance of fragmentation and its effect on biodiversity," the authors write. They say their results also indicate that conservation actions designed to mitigate fragmentation effects can be tailored to the particular regions most likely to host sensitive species. The findings are discussed in more detail in a related Perspective.