Science Puzzle
Why Do We Get Goosebumps?
Step out of a warm shower into a cold room, or hear a sudden noise in the dark, and tiny bumps rise all over your arms. Look closely and each bump has a hair poking out of the middle of it.
What are goosebumps for, and why don't they do us much good?
The Answer
Goosebumps are made to fluff up fur. We just don't have much fur left to fluff.
Every hair grows from a small pocket in the skin called a follicle. Attached to each follicle is a tiny muscle, the arrector pili. When you're cold or frightened, your nervous system makes these muscles contract all at once. Each one tugs its hair upright and pulls the skin around it into a little mound: a goosebump.
In a furry animal this is useful in two quite different ways. Raised fur traps a thicker layer of still air next to the skin; still air is an excellent insulator, so a cold animal stays warmer, rather like pulling on a thicker coat. Raised fur also makes an animal look bigger, which is why a frightened cat puffs up its tail and a porcupine raises its quills.
Our distant ancestors were much hairier than we are. Humans have kept the reflex but lost the thick fur, so our goosebumps trap hardly any air and scare nobody. Biologists call a feature like this vestigial: something inherited from our ancestors that has lost most of the job it once did. The name comes from how the skin looks: just like the skin of a plucked goose.
The principle: Vestigial reflexes. Goosebumps are a reflex inherited from furry ancestors, in whom raising the fur trapped insulating air or made the animal look larger, and on mostly hairless human skin the reflex has lost most of its use.