An organism's reproductive gain factor isn't that sensible a metric of its success. A better one is how adaptable it is. Because of our brains, humans are extr

An organism's reproductive gain factor isn't that sensible a metric of its success. A better one is how adaptable it is. Because of our brains, humans are extremely adaptable. Even with primitive technology we spread throughout the globe, and unlike wild cats or bears we haven't needed to speciate into each climate, develop camouflage fur, etc. The biological investment in an advanced brain gave us the opportunity to thrive everywhere.