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[Ziusudra]

Why is human head hair so much longer than that of other primates?

We don't know. Individual hairs fall out after growing for a while. Some common hypotheses why ours wait longer are:

• When we went upright, the head is the most susceptible to sun exposure, and the hair protects from skin cancer.
• When our brains started burning more calories, we started losing heat mostly from the head, so we needed more insulation.
• That it acts as some sort of mating selection signal, like peacock feathers or a lions mane.
• We went through a semi-aquatic stage and it was some thing for children to grab onto.
• Some sort of touch sense like cat whiskers.

Probably some combination of some of these.

[Frumple]

Genetics, apparently -- the process for determining length is basically the same for other primates as it is for us, ours just is generally more likely to go long.

Why exactly long-head-hair genetics ended up being a thing isn't someone anyone really has an answer for. There's guesses (heat regulation, sexual selection), but lacking a time machine that's all they really are. Could be our height, different hunting methods, different environments (most other primates don't range nearly as far north/south as we do), other stuff. No real way of telling, near as I can recall. Lot of evolutionary history is basically just-so stories at best, making as informed a guess as possible without any real way of surety.

Though there are some other primates with similarly long hair/fur, checking. Not any I noticed with head hair, specifically, but eh. also ninja'd but whatever, it's too close to midnight to care

[Rolan7]

Thanks y'all for looking into it.  Still seems kinda strange, but maybe it really is an adaptation for the savanna sunlight our ancestors flourished in.  Obviously it wouldn't usually grow to the same length it does today since it would be... weathering a lot.  Like fingernails, breaking off under use.
Like when I'm depressed and try to brush with my fingers, and pull away tangles of it.  Painlessly because I'm not an idiot, but still, might explain why it would grow so abundantly.

Did some googling and was looking for an answer more interesting than "sexual selection", but I couldn't. The answer is simply sexual selection, like peacock feathers.

As a consolation prize though, apparently hair and fur are two distinct terms. Fur grows and sheds and replaces itself within a one-year cycle while hair should last for years. Hair was literally something humans invented just to get laid (and protect our heads from the sun)...

That's cool about hair vs fur!
As for it being sexual selection, I kinda have to laugh a little.  Male human hair doesn't grow as fast, so the replacement length tends to be shorter, but it's still easy for a young adult male to have hair down close to the tailbone with proper care.  Past the shoulders at least.  Both of which seem, and I could be wrong, a lot longer than the head-hair of any other primates.

Edit: Ohh, maybe that's why hair is so commonly curly!  To provide more protection!  Which would make straight European hair like mine rather inefficient heh
Edit2:  Counterpoint:  I do get to use it as a scarf in winter.  It's not nothing, either.

[scriver]

Now explain male pattern baldness

[King Zultan]

It's obviously part of a sinister plot by Big Wig, they put chemicals in the water, the chemicals make you go bald, you buy a wig to stop yourself being bald.

[TD1]

The sinister plans of the Whig party never cease.

[TD1]

Occam's straight razor: the tool God employs to make men bald.

[Il Palazzo]

God hath made men in his image. God is a knee, though.

[dragdeler]

It's the principle of parcimony, hairpothesis should not be multiplied without necessecity.

[King Zultan]

Damn we're all destined to be bald because God is bald and he doesn't want anyone to have nicer hair than him.

[Magmacube_tr]

What is a ''safe space''? The Internet term, I mean.

[Il Palazzo]

You know the keyboard? It's the space key, but with a lockable compartment that can hold your bitcoins. It's a safe that's in your space. A safe-space.
It's true.

[None]

One where aggression and bigotry are absolutely not tolerated, usually in protection of some marginalized group. Sometimes used in reference to an online location that does not allow dissenting thought (usually rather important when the thought is something like 'lgbtqia people should have the same rights as cishet people and need a space to discuss their issues,' sometimes used to demean the ideology of a particular internet group that another internet group does not agree or find tolerable (hate groups)). Hard to have a discussion specifically about, say, domestic violence or PTSD if you're similarly allowing people to post whataboutisms to discredit domestic violence victims or share content that triggers PTSD in people.

It indicates a certain expectation of its participants and informs users that particular behaviors will be moderated.

[TamerVirus]

Any space within a safe is safe space

[Uthimienure]

Any space within a safe is safe space

Unless you're locked inside