How do penguins decide who has to stand on the cold outside?

Nobody does. Time-lapse footage shows the mass is not static: every few minutes a tiny wave of movement passes through it, each bird advancing a few centimeters, and the accumulation shifts everyone’s position continuously. The ones outside roll gradually inward and the ones inside come out. It looks like an organized rota and nothing is organizing it.

The problem the huddle solves is worse than it sounds. An incubating male does not eat for about two months, so every calorie he spends on heating is a calorie missing at the end. The dense mass saves an enormous amount of energy, and thermometers inside it read above freezing.

Except that the mass immediately creates a new problem: whoever is on the outer edge is exposed to the wind and pays the price. If the positions were fixed, those birds would freeze while others were comfortable, and that is not a situation that would hold.

What time-lapse filming revealed is that the crowd is not static in the least. Every few minutes a tiny wave of movement passes through it: one bird advances a few centimeters, the neighbor behind follows, and the motion spreads through the whole mass as a traveling wave. The accumulation of those minute steps rolls the outside in and the inside out.

And here is the real lesson. The outcome looks like a fair, organized rota, and there is no reason to assume anyone is running it. Each penguin is simply trying to get closer to the warmth, and the fairness is a by-product of the geometry. This is an observation of an outcome rather than proof of an intention, and that is exactly why it is an interesting model for crowd movement.