system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What are cow licks, why do some people have them while others don't, and why were they evolved?

By why were they evolved I mean why did us humans get them, was it for better vision or something?
gpt
Hair comes out from "follicles" which are little pits in your skin that nourish the hair and make it grow. 

If the follicle doesn't point straight up, then the hair growing out if it won't point straight up either, instead it will grow out at an angle. 

The follicles on most people's heads are arranged in circular patterns called "whorls" where all the follicles slant in the same direction around the circle (if you have ever seen a picture of a crop circle, that's basically the same idea). Most people have several whorls on their heads.

So if you comb or brush your hair in the opposite direction from where it naturally wants to slant towards, your hair will point in a different direction than other hair near it, making a cowlick - but only if your hair isn't too short or too long, and if your hair texture is stiff enough.

You also could get a cowlick where the hairs in two whorls meet, because the hair from one whorl will be coming out of your head in a different direction from the hair next to it.

Nobody is certain why hair evolved to grow in whorl patterns on people's heads. But it probably didn't evolve to help vision since even if you have those whorls, you won't get a cowlick unless your hair is just the right length and you comb it in just the right (wrong) way - so our ancestors probably didn't encounter cowlicks enough for it to influence their survival by keeping hair out of their eyes.

EDIT: Revised paragraph explaining whorls and added paragraph saying you could also get a cowlick where two whorls meet.