Chins are funny. Every human has one; no human knows why.

No other primate (extinct or extant) has a chin. Everyone else’s mouth curves inward at the bottom, making chins a curiously and uniquely human trait. There are a few popular ideas for why chins evolved, but none of them holds water. Or food. None of them holds whatever’s in your mouth like your trusty chin does. The proposals that say chins served an evolutionary purpose (whether mechanical or sexual) don’t hold up to scrutiny, while what seems like the best idea (that chins were simply exposed as our ancestors’ faces shrunk) is difficult to prove. It’s a chin-undrum. (That’s conundrum, but chin.)

All I know, really, is that when I’m outside in a blizzard, I need to keep my chin covered because of our old friend the square-cube law. Chins have a lot of surface area, so they lose heat quickly, but they only get warmed at the same rate as the rest of the body (which has less surface area compared to its volume than a chin does). Combine those and it means that chins, ears, fingers, toes, and noses lose heat faster than it’s supplied.

Emperor Penguins have learned the square-cube law, too; it’s why they huddle by the thousands through the Antarctic winter instead of letting every individual fend for themselves. Each member of the huddle has some of their body exposed to the wind and some exposed to other (warm) penguins. Less heat escapes to the wind than it would if everyone were alone. This shielding works so well, in fact, that the penguins at the center of the huddle can get too warm! They move away from the middle to cool off.

When they move to the edge, those on the edge get to shuffle their way toward the middle. They get to warm up and stay alive after bearing the brunt of the cold, the same way members of a household might rotate shoveling duty when it’s really cold outside so that no one gets frostbitten.

At least, that’s the hope—in both cases.