Much of the study of memes focuses on groups of memes called meme complexes, or memeplexes. Like the gene complexes found in biology, memeplexes are groups of memes that are often found present in the same individual. Applying the theory of Universal Darwinism, memeplexes group together because memes will copy themselves more successfully when they are "teamed up". Examples include sets of memes like singing and guitar playing, or the Christmas tree and Christmas dinner.
Unlike inherited gene complexes, memeplexes do not have to benefit the individuals expressing them in order to replicate. Rather, because memes and memeplexes replicate virally (i.e., by horizontal transmission), they can be beneficial, inconsequential, or pathogenic to their carriers -- memes and memeplexes do not have to be true or useful to replicate.