I saw a post about a sheep that escaped owners/shearing for years and its wool was out of control. Have sheep ever existed in the wild without someone to shear them?
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Because they weren’t this shaggy yet in the wild before they became domesticated. The modern day super-shaggy breeds of sheep that need constant sheering are the result of humans making them like that through artificial selection.
Imagine you’re a human who just figured out how to sew clothes from the hair of that shaggy animal over there so you domesticate it. You like the ones that grow more hair, so those are the ones you tend to breed.
Fast forward 10,000 years and now all the sheep have lost the gene that makes their body hair stop growing. Humans like that mutation and favor it, but the sheep can no longer survive on their own because of that mutation.
As for the technical thing going on, a mammal’s hair follicles are on a slow cycle that toggles back and forth between growth and rest modes. During rest mode the hair doesn’t get longer and it cannot recover from something randomly breaking it off like brushing against a rock or in the case of humans, getting snagged on a bit of clothing. During growth mode it can. The ratio of how much time is spent in each mode decides how long, on average, the hair tends to get before a roll of the dice causes it to get ripped short by *something*. Human genes tend to make hair follicles on the head configured to spend the majority of its time in “growth mode”, while it builds hair follicles on the arms, legs, and naughty places that tends to spend far less of its time in “growth” mode. Thus why you don’t need a haircut for your arms like you do for your head.
Selective breeding of sheep caused us to make their body hair get configured to be stuck in “growth” mode more of the time, like how our head-hair works.
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