Proximal socio-economic drivers of gender equality tend to obscure its remote ecological origins. General systems theory predicts that the greater annual variability in daylength, temperature and daily precipitation at higher latitudes requires greater psychosocial flexibility. We extend this prediction to gender equality as a likely consequence. Accordingly, for 87 pre-industrial societies after 1500 CE, we find more gender equality in more variable habitats, and that this link is mediated by greater subsistence flexibility—foraging rather than raising plants and animals. Mutatis mutandis, these ecological predictors of global gender equality replicate in 175 modern countries after 2000 CE. Gender equality was, and still is, lowest around the Equator, higher toward the North and South Poles, and invariant in east-west direction. The geographical positioning of gender equality in pre-industrial times can predict over 40% of each of the opposite north-south gradients of gender equality in the opposite Northern and Southern Hemispheres today.