"How is that stuff written in the '30s is still copyrighted?"
Google "Mickey Mouse Protection Act." The first, and likely most informative result you'll find will be a Wikipedia article, and with all the angernation being through at Wikipedia here, I won't dare post the direct link here. (See also: my first-ever post as an Anonymous Coward.) The short of it is that the Walt Disney Corporation figuratively has more money than God, and probably literally more money than the Principality of Liechtenstein, and every time the copyright laws in place threaten to release the incarnation of Mickey Mouse into the public domain, they pour that money down Congresscritters's wallets until they vote to extend.
That said, this is all a load of bollocks.
I'm occasionally a writer. Very little of what I write would qualify for original copyright, as most of it is fanfiction (ahem, a "derivative work.") I do, nevertheless, spend an awful lot of time writing, and on dire occasions (such as when my computer is down OH NOES,) I actually write in a notebook. (It's cheaper than crack, and the cramps go away after awhile.)
I once met a friend of mine in a diner whilst doing this, and over a bowl of oatmeal and a plate of eggs, we talked, and she inquired about my notebook. I wouldn't actually let her read the contents thereof, as they aren't fit to publish anywhere minors or those of a weak temperment might read, but as I sat there, eating my eggs, with my notebook opened to a blank page and my pen on the table, she stood up, asked me to move (I complied, sliding down the bench,) and she sat down where I had been seating. She then proceeded to sketch a bust of a woman.
She used my pen, and my notebook; I had already "framed the shot," as it were, given that the notebook and pen were in position to be taken up by someone sitting where I was. Clearly, by this argument, I should own the copyright to the sketch she produced?
I don't think so, and I don't think any reasonable court of law would claim that I do, either.
Anyway, quite frankly, I think copyright is a massive load of bollocks altogether. The only reason it exists in the first place is because of capitalism, which is ALSO a massive load of bollocks. If weak creators didn't have to fear starvation because of more powerful commercial entities (which are MAXIMUM BOLLOCKS) using their works for something and not paying them their due, then powerful creators wouldn't have a bollock-leg to stand on re: extending copyright indefinitely.
Mind you, I'm not saying you should, even in circumstances I might consider ideal, just take something which was made and blow a raspberry to the person who made it, but attribution of effort should suffice, not any of this malarky.
Also, one important implication is being completely ignored here: the freaking monkey took a selfie! Regardless of who owns the bloody copywrong, this seems like an avenue of scientific investigation worth investigating.