The word was invented by Richard Dawkins, an evolutionary biologist. He described ideas as reproducing with variation under selection pressure, which is the definition of the evolutionary mechanism.

There is a more recent use of ‘meme’ to refer to what we used to call an ‘internet image macro’. So the meme of the idea ‘meme’ has itself evolved to have a more specific variant of the general idea.

Memes are inherited. You brush your teeth because your parents do. Memes are subject to selection via biological fitness. The people who didn't brush their teeth died sooner of tooth disease, so those who brushed their teeth had more children. Memes mutate. You don't brush your teeth identically to your parents.