Definition
A meme is a unit of cultural transmission — a tune, idea, catch-phrase, fashion, way of making pots, way of building arches — that propagates from brain to brain by imitation. The term was coined by Richard Dawkins in topic 11 of The Selfish Gene (1976) as a deliberate analogy to gene: a meme is to culture what a gene is to biology.
Memes meet the three properties of replicators: they are copied (via brains, books, media), they vary (most memes mutate substantially during transmission), and they are selected (some spread, others die out). The evolutionary dynamics of memes — meme spread, meme mutation, meme extinction — run in parallel with, and sometimes against, the evolutionary dynamics of genes.
Why it matters
How it works
A new meme is generated (perhaps by a single creative act, perhaps by mutation of an existing meme). It is observed by other brains, which either copy it (with some fidelity) or do not. Copies are observed by further brains, and so on. Selection pressures — what catches attention, what is memorable, what is useful, what is compatible with existing meme inventories — determine which memes spread and which die.
The substrate matters. Memes spreading by oral tradition mutate faster than those preserved in writing. Memes spreading on the internet have shorter generation times than those spreading by book. Different substrates favor different meme properties.