Welcome to the Meme Garden

Ever had a song stuck in your head? For me, it's often a song I hate. But it hangs in there like a tick.
I once had a Boy George song (Karma Chameleon) so firmly ensconced in my mind's ear that I nearly pulled a Vincent van Gogh.
Listen to the song (http://www.youtube.com/watch?v=btRpokScYxs) and tell me if sticks in yours. Listen while you read and then tell me later if it kept playing on a continuous loop.
If you've ever had a song stuck in your head, you've experienced meme replication.
A meme is the noumenal equivalent of a gene, according to Richard Dawkins (http://richarddawkins.net), the British scientist who coined the term.
A gene's number one goal is to replicate itself. That is its evolutionary prerogative. A meme does the same, Dawkins says -- it tries to replicate itself. The difference between the two is that genes have a physical dimension -- memes don't. Genes are phenomena; memes are noumena. Noumena is something that has no physical dimension, but nonetheless exists.
Language is a good example. Right now, I am communicating to you, the reader. I am transmitting ideas. I may be using physical processes to do this (fingers typing on a keypad) and you may be using physical processes to absord what I've written (your eye and brain).
But the ideas being transmitted have no physical qualities. This is noumena. Some of these memes can be simple, like a song, or complex, like an entire language, or a religion. These are ideas that tend to propagate themselves. If they didn't, they would soon cease to exist. So there is an evolutionary function at work.
A simple way of putting it is simply an idea that really catches on. Facebook, Twitter and Youtube are meme factories of epic proportions. You've no doubt heard of a Youtube posting going viral (Eg. "If you touch my junk, I'm going to have you arrested.") The word "viral" is apropos, I think, given that memes are really like noumenal viruses.
There is something in a meme that wants to repeat itself, and in the repetition, it often morphs into something else. And by using the word "want" I do not mean to suggest that there is some higher intelligence behind meme propagation. It's just how things evolved, and it was a result of human consciousness, although I suppose it could be said that, even at the animal level, we see meme replication (birdsong comes to mind).
Sadly, it's not just the good ideas or good songs that go viral. Indeed, it's often the trite and trivial that becomes popular, simply because it is so easy to grasp.
And that is the one irony of Dawkins' meme theory. The very theory that explains how ideas and language and music and religion and science evolve and propagate seems to be having a hard time making its way into our nomenclature.