From Richard Dawkins, The Blind Watchmaker, p. 157:
In The Selfish Gene I speculated that we may now be on the threshold of a new kind of genetic takeover. DNA replicators built 'survival machines' for themselves—the bodies of liming organisms including ourselves. As part of their equipments, bodies evolved on-borard computers—brains. Brains evolved the capacity to communicate with other brains by means of language and cultural traditions. But the new milieu of cultural tradition opens up new possibilities for self-replicating entities. The new replicators are not DNA and they are not clay crystals. They are patterns of information that can thrive only in brains or the artificially manufactured products of brains—books, computers, and so on. but, given that brains, boooks and computers exist, these new replicators, which I called memes to distinguish them from genes, can propagate themselves from brain to brain, from brain to book, from book to brain, from brain to computer, from computer to computer. As they propagate they can change—mutate. And perhaps 'mutant' memes can exert the kind of influence that I am here calling 'replicator power'. Remember that this means any kind of influence affecting their own likelihood of being propagated. Evolution under the influence of the new replicators—memic evolution—is in its infancy. It is manifested in the pehnomena that we call cultural evolution. Cultural evolution is many orders of magnitude faster than DNA-based evolution, which sets one even more to thinking about the idea of 'takeover'. And if a new kind of replicator takeover is beginning, it is conceivable that it will take off so far as to leave its parent DNA (and its grandparent clay if Cairns-Smith is right) far behind. If so, we may be sure that computers will be in the van.
From E. O. Wilson's Consilience, p. 136:
The natural elements of culture can be reasonably supposed to be the hierarchically arranged components of semantic memory, encoded by discrete neural circuits awaiting identification. The notion of a culture unit, the most basic concept of all, has been around for over thirty years, and has been dubbed by different authors variously as mnemotype, idea, idene, meme, sociogene, concept, culturgen, and culture type. The one label that has caught on the most, and for which I now vote to be winner, is meme, introduced by Richard Dawkins in his influential work The Selfish Gene in 1976.
The definition of meme I suggest is nevertheless more focused and somewhat different from that of Dawkins. It is the one posed by the theoretical biologist Charles J. Lumsden and myself in 1981, when we outlined the first full theory of gene-culture coevolution. We recommended that the unit of culture—now called meme—be the same as the node of semantic memory and its correlates in brain activity. The level of the node, whether concept (the simplest recognizable unit), proposition, or schema, determines the complexity of the idea, behavior, or artifact that it helps to sustain in the culture at large.
I realize that with advances in the neuroscience and psychology the notion of node-as-meme, and perhaps even the distinction between episodic and semantic memory, are likely to give way to more sophisticated and complex taxonomies. I realize also that the assignment of the unit of culture to neuroscience might seem at first an attempt to short-circuit semiotics, the formal study of all forms of communication. That objection would be unjustified. My purpose in this exposition is the opposite, to establish the plausibility of the central program of consilience, in this instance the causal connections between semiotics and biology. If the connections can be established empirically, then future discoveries concerning the nodes of semantic memory will correspondingly sharpen the definition of memes. Such an advance will enrich, not replace, semiotics.
From Eric Chaisson's Epic of Evolution, pp. 424-25:
Cultural evolution tracks the changes in the ways, means, actions, and ideas of society, including their transmission from one generation to another. Called "memes" by some, in loose analogy to genes, these are cultural replicators, such as a new word or song invented by one person and mimicked by others. To be sure, many of the cultural traits already noted, including the construction of useful tools, the theaching of elaborate language, the practice of viable agriculture, and not least the discovery of controlled energy, have been initiated and refined over scores of generations. The bulk of this newfound knowledge was transmitted to succeeding offspring not by any genetic-directed inheritance but by its use and disuse of information available to intelligent beings.
A mostly Lamarckian process (based on the ideas of the nineteenth-century French evolutionist, Jean-Baptiste de Lamarck), cultural evolution proceeds via the passage of acquired attributes. Like galactic, stellar, and planetary evolution before it, cultural evolution involves no molecular reactions as in chemical evolution and none of the genetic inheritance typical of biological evolution. Culture enables animals to transmit favourable traits and survival skills to their offspring by non-genetic routes. Information gets passed on behaviorally, from brain to brain. Human culture itself is shaped by the sum total of human minds, often acting imitatively and cooperatively, sometimes over the ages but at other times in a single generation. The upshot is that cultural evolution acts much faster than biological evolution. Genetic selection operates little, if at all, in evolutionary realms sandwiching neo-Darwinism, where adaptive and selective pressures clearly predominate. Even so, a kind of selection was, and is, at work culturally. The ability to start a fire or throw a spear, for example, would have been a major selective asset for those hominids who possessed them, an asset transmitted not by genes but by memes. Perhaps more than anything else, memes are what sets us apart from other species.
Memes e intertextualidad