Major evolutionary transitions have been driven by climate change. The physical evolution of the genus Homo was spurred by the onset of the ice age regime of the Pleistocene. The climate transition to the relatively warm and stable Holocene ushered in agriculture, large-scale hierarchical societies, and the current human domination of planet earth. We are now at the beginning of another major change in the earth’s climate regime. We think of humans as being a warm weather species because we evolved in the tropics. But compared to the rest of the Cenozoic (66 mya to the present), the last few million years have been very cold. We became human in the ice age Pleistocene. Human economic activity will drive levels of atmospheric CO2, and eventually global temperatures, to levels not seen for tens of millions of years. If evolutionary history is any guide, current social and economic systems, and the values supporting those systems, will be maladaptive in the new climate regime. If we dive deep into our evolutionary past, however, there is hope for our species. The extreme variation of the Pleistocene climate gave us humans two traits that might help us adapt to the post-Holocene world. These are the flexibility to deal with radical environmental change and the ability to cooperate with other groups.