structural:summarization, structural:reformatting
Memetic lifecycle: transmission, retention

Memes, analogously to genes, vary in their aptitude to replicate; successful memes remain and spread, whereas unfit ones stall and are forgotten. Thus, memes that prove more effective at replicating and surviving are selected in the meme pool.

Memes first need retention. The longer a meme stays in its hosts, the higher its chances of propagation are. When a host uses a meme, the meme's life is extended. The reuse of the neural space hosting a certain meme's copy to host different memes is the greatest threat to that meme's copy. A meme that increases the longevity of its hosts will generally survive longer. On the contrary, a meme that shortens the longevity of its hosts will tend to disappear faster. However, as hosts are mortal, retention is not sufficient to perpetuate a meme in the long term; memes also need transmission.

Life-forms can transmit information both vertically (from parent to child, via replication of genes) and horizontally (through viruses and other means).Memes can replicate vertically or horizontally within a single biological generation. They may also lie dormant for long periods of time.

Memes reproduce by copying from a nervous system to another one, either by communication or imitation. Imitation often involves the copying of an observed behavior of another individual. Communication may be direct or indirect, where memes transmit from one individual to another through a copy recorded in an inanimate source, such as a book or a musical score. Adam McNamara has suggested that memes can be thereby classified as either internal or external memes (i-memes or e-memes).

Some commentators have likened the transmission of memes to the spread of contagions. Social contagions such as fads, hysteria, copycat crime, and copycat suicide exemplify memes seen as the contagious imitation of ideas. Observers distinguish the contagious imitation of memes from instinctively contagious phenomena such as yawning and laughing, which they consider innate (rather than socially learned) behaviors.

Aaron Lynch described seven general patterns of meme transmission, or "thought contagion":