RESUMO
There is a curious paradox in the evolutionary legacy of Ice Ages. Studies of modern species suggest that they are currently evolving in response to changing environments. If extrapolated into the context of Quaternary Ice Ages, this evidence would suggest that the frequent climatic changes should have stimulated the evolutionary process and thus increased the rates of change within species and the number of speciation events. Extinction rates would, similarly, be high. Quaternary insect studies call into question these interpretations. They indicate that insect species show a remarkable degree of stability throughout the Ice Age climatic oscillations. The paradox arises from the apparent contradiction between abundant evidence of incipient speciation in insect populations at the present day and the evidence that, in the geological past, this apparently did not lead to sustained evolution.
Assuntos
Evolução Biológica , Clima , Meio Ambiente , Insetos/genética , Animais , Especificidade da EspécieRESUMO
In the British Quaternary, two post-Cromerian interglacials, the Hoxnian and the Ipswichian, are recognized. Evidence of additional interglacials in this interval is widely accepted in the oceanic record of Quaternary events, and the possibility that at least one additional interglacial of this age is represented in Britain has been discussed. However, in the absence of datable interglacial deposits which are seen to overlie one another, the issue has remained controversial. We describe here deposits at Marsworth, UK (Fig. 1) where there is evidence of two temperate episodes, and of intervening periglacial conditions. Stratigraphical superposition is established beyond any reasonable doubt. The later deposit relates to the temperate woodland stage of the Ipswichian Interglacial. Dating of the earlier temperate material by the 230Th/234U disequilibrium method indicates an interglacial episode not previously established in the British Quaternary.