A Succinct Definition of a Meme
Memes are ideas that are replicated, have variation, and are subject to selection, making them things that can evolve.
For something to count as a replicator it must sustain the evolutionary algorithm based on variation, selection and retention (or heredity). Memes certainly come with variation - stories are rarely told exactly the same way twice, no two buildings are absolutely identical, and every conversation is unique - and when memes are passed on, the copying is not always perfect. As the psychologist, Sir Frederic Bartlett (1932) showed n the 1930s, a story get a bit embellished or the details are forgotten every time it is passed on. There is memetic selection - some memes grab the attention, are faithfully remembered and passed on to other people, while others fail to get copied at all. Then, when memes are passed on there is retention of some of the ideas or behaviors in that meme - something of the original meme must be retained for us to call it imitation or copying or learning by example. The meme therefore fits perfectly into Dawkin's idea of a replicator and into Dennett's evolutionary algorithm.