The failure of evolution: Late quaternary mammalian extinctions in the holarctic

Abstract

The ‘mass extinction’ of large mammals (‘megafauna’) in the late Pleistocene can be viewed as the failure of evolution to adapt to climatic and/or biotic changes. Extinctions before the Last Cold Stage, affecting both large and small mammals, were mostly balanced by evolution or immigration of new species. However, in the late Pleistocene extinctions occurred at a greatly accelerated rate, seriously depleting the ‘megafauna’ on a global scale. Extinctions were most severe in North America, South America and Australia, moderate in northern Eurasia and slight in sub-Saharan Africa where the largest mammals survive today. In northern Eurasia two phases of extinction can be recognized: (1) extinction pre-ca. 20,000 BP of ‘interglacial survivors’ confined to Southern Europe; and (2) extinction within ca. 14–10,000 BP of larger group of more or less cold-adapted species. In North America many more species became extinct, all or most within the period ca. 11,500-10,500 BP. Compared with Europe, where extinctions were moderate and staggered, those in North America were severe and sudden. Both late Pleistocene environmental changes and ‘overkill’ by Upper Palaeolithic hunters have been blamed for extinctions, but neither hypothesis alone is adequate for northern Eurasia and North America. A third hypothesis, involving interaction of environmental changes with human predation appears consistent with available data. A much greater body of accurate data is required before we can hope to determine the cause or causes of late Pleistocene extinctions on a global scale.