ANOTHER WAY INTO THE STORYExplore by subjectEnter through a question, then return to the wider evolutionary trajectory.Climate, geography & ancestryShared ancestry, diverging circumstancesAfrica becomes a changing landscapeLeaving continuous canopy without abandoning treesRefuges that could themselves become stressfulWater chemistry, sweating & mineral balanceWhen water carries an increasing salt burdenThe mineral cost of terrestrial lifeSmall bodies, early meat and an expensive brainBody hair, scalp hair & infant transportThe mineral cost of terrestrial lifeAn infant needs a secure holdFire, cooking, body size & animal foodsSmall bodies, early meat and an expensive brainCold nights, fire and the metabolic staircaseCaffeine, AHR & physiological toleranceRefuges that could themselves become stressfulTolerating the fallback resourceThe proposed accelerated neural pathwayBrain expansion & the proposed scaling principleThe slow pathway: demands on a finite neuronThe proposed accelerated neural pathwayWhy acceleration would diminish—and what remains unresolvedNeanderthals, Denisovans & population mixingDifferent lineages, different selective histories