This research empirically establishes that interpersonal population diversity helps explain worldwide differences in climate change policies. It advances the hypothesis that heterogeneity in the composition of genetic traits, originating from the prehistoric course of the exodus of Homo sapiens from East Africa tens of thousands of years ago, is a major barrier to implementing stringent climate-friendly policies and measures. The underlying intuition is that genetically fragmented societies, characterized by mistrust, preference heterogeneity and persistent poor-quality institutions, find it difficult to sustain collective climate action. Using data for 84 world economies, I find evidence that prehistorically determined genetic diversity has a negative influence on the stringency of climate-related policies and measures. Furthermore, I document that descendants of ancestral societies with greater genetic diversity are less likely to exhibit pro-climate behavior, consistent with a mechanism of inter-generational transmission of cultural norms of mistrust and non-cooperation. The findings suggest that strengthening national responses to changing climate conditions requires considering the long-term legacy of interpersonal population diversity.