In comics, DC & Marvel introducing Swamp Thing & Man-Thing within a month or two of each other.
Well, this one's a little more questionable. Conway and Wein were actually roommates at the time, and there might've been some actual overlap as a result, that might not be a "pulled similar ideas out of the ether purely out of nowhere" thing. Not that either necessarily outright copied the other, but they might've tossed ideas back and forth and one hooked on something similar to what the other was doing without realizing it.
Well, yes they were roommates at the time, but both Conway and Wein have said that they didn't really talk about their stories with each other.
I just pulled out my copy of Jon B. Cooke's Swampmen (which is really spectacular, and anybody with a passing interest in Swamp Thing, Man-Thing, or swamp monsters in general should buy it), and here's what Wein has to say about conceiving the first, one-shot Swamp Thing story:
(p. 76) Well, I wish I had a better story, but it's as simple as this: I was on the subway on my way into the DC office and I needed something to pitch to Joe.* I didn't have any ideas that came to me in the subway out of the blue. I honestly don't know where it came from.
*Joe Orlando, editor of House of Secrets.
*Joe Orlando, editor of House of Secrets.
I've interviewed both Wein and Conway in the last couple of years, and I can tell you that they're both pretty straightforward guys who, if they'd inspired each other's stories, would be upfront about it.
Interestingly, Wein was the guy who ended up adding the thing that really differentiated the two characters: The concept of "Whoever knows fear, burns at the Man-Thing's touch." In the first Man-Thing story by Conway, anyone that the Man-Thing touched burned. Wein scripted the second Man-Thing story, and realized that a protagonist who could never touch anybody would quickly become very limiting.
So basically, this is my long-winded way of saying that even though the two of them were living together at the time, any similarities between Swamp Thing and Man-Thing were still just a coincidence.

Sorry for the digression.