The sixth mass extinction: Anthropocene and the human impact on biodiversity

Mass extinctions are a major pattern in mac- roevolution. Because of their frequency, quickness and global effects, they shaped the global biodiversity several times during the geological ages. As an integrative factor with respect to microevolutionary Neo-Darwinian pro- cesses, mass extinctions are probably due to a set of dif- ferent possible causes (basaltic super-eruptions, impacts of asteroids, global climate changes, continent drifts, and so on). An analogy has been proposed. If we compare the rates and amounts of extinction during those singular evolutionary events with the range of species losses over the past few centuries and millennia in human times, we see a similar trend. Then, according to a group of author- itative evolutionists like Edward O. Wilson and Niles El- dredge, we have evidence that humans are now causing the so called ‘‘Sixth Mass Extinction’’. ‘‘Anthropocene’’ also means that Homo sapiens has become a dominant evolu- tionary force. Through a mix of different significantly impacting activities (i.e., fragmentation of habitats, over- population, chemical pollution, invasive species, over- exploitation of resources in hunting and fishing), we have produced the conditions for a serious extinction crisis. According to Nature (March 2011), the sixth mass extinction is under way: ‘‘we find that Earth could reach that extreme within just a few centuries if current threats to many species are not alleviated’’ (Barnosky et al. 2011). We discuss here a recent model for mass extinctions (the ‘‘Perfect Storm Model’’), based on the idea that these macroevolutionary patterns could be produced by a mix of three main simultaneous causes and conditions.