The expression ‘red in tooth and claw’ is metaphor often used to depict conditions during the Stone Age. Moreover, Tennyson's anguished cry against the brutality of life is often seen as a riposte to Darwinism and the whole conception of evolution. In truth, although Tennyson was deeply hostile to Darwin's evolutionary theories, he wrote his famous poem as an intensely personal expression of his sense of loss at the death of his dear friend A. H. Hallam, and this was first published nine years before Darwin published his greatest work, On the Origin of Species. Nevertheless, the powerful image of the awful inevitability of evolutionary processes provides a good point to embark upon the task of exploring how climate change influenced the evolution of modern humans.

The emergence of modern humans from Africa is a good starting point for considering the evolutionary implications of the ice age for our species. Clearly this choice is arbitrary. But, as has been made clear in the preceding chapter, our knowledge of both the timing of this movement and its details in the early stages is at best fragmentary.