Re: Goose bumps -- why -- not how -- do we have them?

The reason why we have goose bumps is that the animals from which we evolved had goose bumps.

The goosebumps evolved in the other animals as part of the sympathetic (fight or flight) response. When animals are cold, the response lifts the hairs up, so that the hair do a better job of insulating the skin. In different animals, the hairs also rise in response to fear. For example, when cats are threatened (by a dog, for example), their hair becomes erect and their backs arch. This makes the cat appear bigger than it is. Porcupines also have a similar reaction.

So when people are scared, excited or cold (all conditions that cause the sympathetic nervous system to get active), people can get goosebumps.

Because people evolved from other animals that have this as part of their sympathetic response, humans do too.

Here are some references. The first is from Scientific American. The second is from a journal that talks about goosebumps in mice, so goosebumps appear to be common among mammals (including chimps, one of our closest relatives, porcupines, cats and mice):
http://www.sciam.com/article.cfm?id=why-do-humans-get-goosebu
http://www.ncbi.nlm.nih.gov/pubmed/10480027

Thanks for your very intersting question.

Jeff