Questioning the sixth mass extinction
John J. Wiens, Kristen E. Saban
Abstract
The idea that Earth is currently experiencing a sixth mass extinction is widespread. We critically evaluate this claim. Very few studies have tested this idea. Some studies showed that recent extinction rates are faster than fossil background rates, but extinction rates can exceed background rates outside mass extinctions. Other studies extrapolated from recent extinctions to project 75% global species loss. But these recent extinctions were mostly of island species. No cause was specified for these future extinctions, and >50% of assessed species are considered non-threatened. We find numerous other issues. Proponents of the sixth mass extinction have made invaluable contributions by highlighting recent extinctions, but these extinctions may not be equivalent to past mass extinctions or relevant to current threats.