I’ve noticed that when I’m really cold or sometimes when I’m scared, I get these tiny bumps all over my skin, which I think are called goosebumps. Why does this happen? What’s the biological reason behind it?
In: Biology
It’s a trait left over from before humans lost all of their body hair. The goosebumps form as a result of tiny muscles in your skin trying to make the hairs on your skin stick up, which when cold helps to create a layer of insulating air to reduce heat loss, and when scared helps to make you look larger and more threatening to any potential predators. Both of these aren’t particularly effective in humans because of our lack of significant body hair, but there wasn’t any evolutionary incentive to get rid of them so they just stuck around.
Goose bumps are a vestigial feature in humans.
Vestigial means they used to have a purpose, but don’t anymore.
Goose bumps had a purpose in humans when we were much hairer than we are now. When we were cold, it would puff up our hair to give us a thicker layer of insulation from the cold.
When we were scared it would puff us up and make us look bigger and more intimidating. Just like how cats get puffier when they’re frightened.
Now we don’t have enough hair for it to do anything useful, but the reflex still remains because it’s not harmful so we don’t evolve out of it.
The posterior hypothalamus is the region that is invovlved in thermoregulation- it warms the body when it is cold by shivering, shunting blood to the core and raising body hair. All of these reactions (plus sweating, modulated by anterior hypothalamus that cools the body) are advantageous when you are being attacked by predators, by making you more jumpy, less prone to bleeding, cutting and making you slippery- so those reactions from the same regions of the hypothalamus are also part of the fear response.
Your body is covered in hair. Every hair has a muscle (the arrector pilli) around the base of the follicle. [Each “goosebump” is the muscle around the base of one hair contracting, which makes that hair stand up](https://www.researchgate.net/publication/343051431/figure/fig2/AS:915950454988801@1595391014202/Sympathetically-innervated-arrector-pili-muscle-contraction-causes-goosebumps-a-visible.png) rather than laying flat like normal.
This is a leftover reflex from when our ancestors had much more body hair everywhere. If your body still had hair like that, [“goosebumps” would look like this.](https://www.shutterstock.com/shutterstock/photos/268930307/display_1500/stock-photo-the-cat-s-hair-bristled-up-when-it-saw-the-dog-268930307.jpg)
When you’re cold, the puffed up hair traps a layer of air against the skin, providing an insulating barrier layer to help keep warmer.
When you’re scared/threatened, being puffed up makes you look bigger and hopefully wards off whatever is threatening you. It also signals “hey, I see you and I’m prepared to fight”.
You can still see [cold animals puffing up their fur](https://s3.us-east-2.amazonaws.com/journeynorth.org/images/graphics/robin/randyindish/winter2_full.jpg) and cats and [dogs using their goosebump-produced raised hair](https://www.silentconversations.com/wp-content/uploads/2023/03/silentconversations_piloerection_comp2.jpg) today. Modern humans don’t have much body hair, so you see the muscle bumps and not the raised hair and it doesn’t actually do much. Now it’s just a reminder that we’re a bunch of naked apes, no so far removed from other animals.
Why do we get goosebumps when listening to good music?
The fear reaction is the same as when a dog or cat raises its hackles when threatened. It makes them look larger and more intimidating, it’s just that we aren’t covered in fur anymore so it’s not obvious.
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