Not sure what the original source of the first one is, but it looks like the original tree-swing concept goes back to the 70's or earlier. Here are the source links for proper author credit (and link reliability). 

http://www.businessballs.com/treeswing.htm (Closest I could find. Touches on their suspected origins of the comic)

http://xkcd.com/292/

http://xkcd.com/1425/

http://www.brainstuck.com/2009/02/27/mysql/

https://xkcd.com/664/

http://xkcd.com/208/

And no, I don't have anything better to do on a Sunday night. =p

--

Wyatt Zacharias

On Sun, May 31, 2015 at 11:33 PM, Trevor Cordes <trevor@tecnopolis.ca> wrote:

https://d262ilb51hltx0.cloudfront.net/max/800/1*clNnjwwKcm0p5Qmsz7T5fg.png
https://d262ilb51hltx0.cloudfront.net/max/800/1*29M-_cVKMtf_mm7hpzvx8w.png
https://d262ilb51hltx0.cloudfront.net/max/800/1*_zT3FH-ZmuxxAT0cQKvNHg.png
https://d262ilb51hltx0.cloudfront.net/max/800/1*BnIZYfFDTQUYnL5yHpuldw.jpeg
https://d262ilb51hltx0.cloudfront.net/max/800/1*qUnA1tkRQ6qeUZP6Wxd_yQ.png
https://d262ilb51hltx0.cloudfront.net/max/800/1*oGaYyDJNEZ6UL5nN-43YMg.png

funny!

I hope those links work for longer than just the page view I did...
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