I was watching a BBC natural history programme the other night, and it included an extract from David Attenborough's Life in the Freezer series about life in Antarctica. This classic scene shows a flock of (male) Emperor penguins huddled together on the ice in a winter blizzard. The commentary explains that the male penguins incubate the egg, holding it on their feet to keep it off the ice. As the icy wind blows, penguins gradually peel away from the windward side of the group and waddle round to the sheltered leeward side. As the voiceover explains, they are 'taking it in their turn on the outside to suffer the harshest conditions' (or some such phrase).

But hang on... as good Darwinian I must protest! Why should individual penguins 'take their turn' on the outside if they could help it?

I haven't got the scene on tape to re-view it, but from memory I think the following account would be consistent with the facts: each penguin has the following order of preference: (1) on the inside of the huddle (2) on the leeward side (3) on the windward side. At the beginning of the brooding period the biggest, butchest penguins muscle their way to the inside. But as soon as the wind blows, penguins on the windward side slowly waddle round the outside until they reach the leeward, which means that some of the leeward penguins are no longer on the outside. (They can't move very fast, because they have to keep the egg balanced on their feet.) This exposes more penguins to the wind, so they in turn move round. Eventually, some of the butch penguins in the middle are exposed, but it is not worth the effort and danger of trying to muscle their way in again, so they also move round. Over a period of time, all the penguins spend some time in each position in the group, but this is not a result of any noble propensity to share the worst positions, just a side effect of the selfish movements of all, combined with the constraints of moving while carrying an egg!

I wonder if any penguin expert has considered this? The test would be to observe the movement of the group as a whole: if I am right, the centre of the group will gradually move in the same direction as the wind. Of course, if the wind shifts, so will the group.