In the interests of having something personal to justify this category, though, I'll start with a personal anecdote: Jehovah's Witnesses came by this morning shortly before my hiatus. Not terribly notable in and of itself, of course, but it was actually the first time I've seen them go door-to-door, so kinda exciting. But it got me thinking on the subject of memes.
A little background first: in the mid-19th century, the idea of evolution, in a broad sense - that is, that life used to take different forms than it does now, and that it has somehow developed from those forms into the ones it has now - was generally accepted. But the mechanism behind it was not really known. The most widely accepted theories were those proposed by Jean-Baptiste Lamarck at the beginning of the century: first, that creatures developed certain aspects of their physiologies over the course of their lives and passed them on to their offspring (so a proto-giraffe, stretching its neck to reach leaves, would have children with slightly longer necks than the parents were born with); or, alternately, that there was simply some élan vital that made animals develop and complexify (so successive generations of giraffes would simply have longer necks because, well, that is how their élan tells them to develop). The problem was that the first option (inheritance of acquired characteristics) had a lack of evidence - the children of blacksmiths being born not particularly more muscly then their peers, for instance - and the second (generally just called Lamarckian Evolution) was really just a way of passing the buck into philosophical realms where science couldn't meaningfully argue with it.
In 1859 Charles Darwin, an English naturalist, published a book titled On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (now generally just called On the Origin of Species) in which he proposed a third theory. All creatures, he argued, produce far more offspring than could ever survive to adulthood. Some of them will live long enough to produce the new generation; most will die. Which ones survive? Well, those best adapted to the environment; proto-giraffes with longer necks will have access to more food than their shorter compatriots, be healthier and get more mates (who will also tend to be longer-necked) and their kids, although still having a variety of neck lengths, will on average have necks ever so slightly longer than their parents' generation. Darwin's theory ("Natural Selection") was so eminently testable, was presented with so much evidence (Darwin held off publication for the better part of two decades, never feeling that his increasingly mountainous pile of evidence was enough, until the possibility of being scooped by a colleague* finally prompted him to publish) and above all made so much sense, that it almost immediately became the dominant paradigm of biology, a position it has held ever since.
Then, in the 1970s, a man named Richard Dawkins had an interesting thought about natural selection. Who said it only applies to living things? After all, ideas behave much like animals do: they spread, reproduce, mutate, survive at different rates based on their adaptation to the environment. Dawkins formalized this into the idea of memes (by analogy to genes; it's pronounced "meem"). Perhaps the quintessential example of a meme is a chain-letter or -email. A meme is born, or develops out of an old one: somebody creates a joke and forwards it to some friends. It spreads, passing from person to person, mutating along the way; mutations occur as people change or add or misinterpret or do whatever to the meme. Those mutations that help pass it on (to a chain-letter, perhaps polishing the joke at the core or adding a plea to forward it) are propagated more and faster, and thus take up more and more space relative to the original; mutations that harm its propagation (say, accidentally snipping the joke out entirely) occur as well but die off quickly. As time goes on, natural selection pushes the meme in the direction of better and better reproduction, just like it does to living things; and this is good, because there is a limit to how many chain letters you can forward in a day, so the joke has to not only be good but also be better than any other joke you could be telling in order to get passed on.
But of course memes aren't just limited to chain letters, even if they provide the most clear-cut example. Dawkins pointed out that pretty much anything that might be loosely qualified as an "idea" could be considered as a meme. Fashions are memes: they are created, spread, mutate, and eventually are replaced by other fashions, which (in some hard-to-define way) are better adapted to the environment of people's fashion choices. So are, say, phrases: the "best laid plans" quote towards the top of the post is an example of a meme, spreading through writing and conversation; at one point it lost the Scots dialect ending ("gang aft a-gley") and the new version, despite the weakness of making its ending implicit, outcompeted its progenitor. Philosophical concepts are memes too, as are political ones: communism, for example, mutated out of socialism into a more aggressively expansionist version; developed secondary characteristics (Soviet state education, the Comintern) to help keep up propagation; mutated into new varieties, some of which flourished (eg, Marxism-Leninism), some of which failed due to an inability to reproduce fast enough to stay competitive (Anarcho-Communism), and some of which failed due to changing environmental conditions outside their control (Trotskyism); and finally, the whole environment changed rapidly, outpacing the mutability of the family of communist memes to keep up, replacing them en masse with other memes (largely various species of libertarian capitalism and light authoritarianism). Finally, to take this post back to the opening anecdote, religions can be treated as memes too**; Jehovah's Witnesses (Jehovah's Witnessing? Jehovah's Witnessism?), for example, is a competitive religious meme not least because of its explicit commands to evangelism.
Finally, the internet turns out to be a great breeding ground for memes. People on the internet tend to have plenty of free time, plenty of desire to converse, and with practically real-time connectivity can spread memes around very quickly. The intro to the video game Zero Wing, for instance, was so badly translated that people began referencing it all over the internet, the phrase "All your base are belong to us" in particular becoming a fast spreading meme. After a while, the phrase became seen as boring or old, and mainly died off. There are dozens - probably hundreds - of other memes floating around the internet: rickrolling (innocuous-seeming or downright misleadingly-labelled links to the music video of "Never Going To Give You Up" by Rick Astley), lolcats (weirdly labelled pictures of cats), de-motivational posters (long since mutated to include pretty much anything in the "picture, black frame, label" model), and many, many more.
...And of course, the idea of internet memes (like the concept of memes itself) is a meme in its own right: spreading from person to person, via things like this blog post, and continuing to occupy a niche in the mental environment as long as people continue to pass it on. Memetics never really turned into a science in the sense Dawkins probably imagined back in 1976, but it remains a pretty neat concept to think about and throw around occasionally.
*Alfred Russell Wallace.
**Dawkins has since become an outspoken and frankly irritatingly evangelistic atheist; his reductionistic view of religions as memes only is probably related to this.
