This comic is calling into question the accuracy of Wikipedia. This is a favorite past-time of librarians and professional researchers, and not usually one of Randall's. But, to take it seriously for a moment: People, Wikipedia is editable by anyone. If you are doing serious work, follow through the citations, and decide which are from upstanding sources, and which are just people writing on their blog, and which are people writing on their blog who know what they are talking about.
The title of the comic is a play on the word cytogenesis. Cytogenesis is the formation of cells and their development. Citogenesis, on the other hand is a portmanteau of 'Citation' and 'Genesis'. Citation meaning quoting a source. Genesis being the origin of something. So, citogenesis would be the creation of a quote that can be used to back-up a fact or statement.
The comic is discussing citogenesis occurring on Wikipedia. Wikipedia is a free and freely editable encyclopedia that aims to become the most complete and correct knowledge base available, in all languages, to all people. Wikipedia is managed by the Wikimedia Foundation who publish MediaWiki, a web-based wiki engine written in PHP. The explain xkcd wiki is run on a MediaWiki server.
- Where Citations Come From:
- Citogenesis Step #1
- Through a convoluted process, a user's brain generates facts. These are typed into Wikipedia.
- [A guy with short hair sits at a desk, typing on a laptop.]
- Guy: (typing) The "scroll lock" key was designed by future Energy Secretary Steven Chu in a college project.
- A rushed writer checks Wikipedia for a summary of their subject.
- [Ponytail sits at a desk, typing on a desktop.]
- Ponytail: (typing) US Energy Secretary Steven Chu, (Nobel Prizewinner and creator of the ubiquitous "scroll lock" key) testified before Congress today...
- Step #2
- Surprised readers check Wikipedia, see the claim, and flag it for review. A passing editor finds the piece and adds it as a citation.
- [Cueball sits on a couch with a laptop in his lap, typing.]
- Cueball: Google is your friend, people. (typing) 
<ref>tags exist, but no
<references/>tag was found