Decade after decade, though the political landscape changes, Republicans and Democrats remain more or less equally balanced in the fight for political power. The Economist’s Lexington column this week tries to explain this effect, asking “Why is the country divided so evenly?”

The analogy with sex ratios in biology suggests to me that the explanation may be dynamical as well as political. The familiar paradox is that to maximize offspring, humanity would do better to have 10 women for every man, but that’s not how it happens. In such a world, men would end up with many more descendants than women. This would give a huge selection advantage to parents who gave birth to more than the usual small fraction of boy babies, quickly pushing the ratio back towards 1:1.

With political parties it won’t be as clean or as reliable, but I imagine there may be an analogous dynamic in play.

[7 January 2023]