Different mechanisms of evolution
Though memetic and genetic evolution are subjected to the same basic principles of blind variation and natural selection on the basis of fitness, memetic evolution is basically a much more flexible mechanism. Genes can only be transmitted from parents (or parent in the case of asexual reproduction) to offspring. Memes can in principle be transmitted between any two individuals (though it will become more difficult the larger the differences in cognitive mechanisms and language are). (this is sometimes called "multiple parenting").
For genes to be transmitted, you typically need one generation, which for higher organism means several years. Memes can be transmitted in the space of hours. Meme spreading is also much faster than gene spreading, because gene replication is restricted by the rather small number of offspring a single parent can have, whereas the amount of individuals that can take over a meme from a single individual is almost unlimited. Moreover, it seems much easier for memes to undergo variation, since the information in the nervous system is more plastic than that in the DNA, and since individuals can come into contact with much more different sources of novel memes. On the other hand, selection processes can be more efficient because of "vicarious" selection (Campbell, 1974): the meme carrier himself does not need to be killed in order to eliminate an inadequate meme; it can suffice that he witnesses or hears about the troubles of another individual due to that same meme.
The conclusion is that memetic evolution will be several orders of magnitude faster and more efficient than genetic evolution. It should not surprise us then that during the last ten thousand years, humans have almost not changed on the genetic level, whereas their culture (i.e. the total set of memes) has undergone the most radical developments. In practice the superior "evolvability" of memes would also mean that in cases where genetic and memetic replicators are in competition, we would expect the memes to win in the long term, even though the genes would start with the advantage of a well-established, stable structure. This explains why sociobiological models of human behavior can only
be partially correct, as they neglect memetic factors.
Different selection criteria
When memetic and genetic fitness criteria are inconsistent, the different
implicit objectives of memes and genes will lead to a direct competition for
control of the carrier's behavior. Both replicators have similar aims to the degree that they use the same vehicles: individual organisms. Everything that strengthens the vehicles should in general be good for the replicators, and hence both genes and memes should be selected on the basis of their support for increased survivability and reproducability of their carriers. However, the implicit goals of genes and memes are different to the degree that they use different mechanisms for spreading from one vehicle to another one. Memes will be positively selected mainly for increased communicability. Genes will be selected mainly for sexual reproducability. These different emphases may lead to direct conflicts.
For example, priests in many religions are prohibited to marry and to have children, in striking disagreement with genetic injunctions. Yet we can easily imagine that the religious meme of celibacy would have been selected because unmarried priests can spend more time and energy on "spreading the word", and hence replicating the meme.
An even more vivid example of countergenetic behavior, closely related to the issue of altruism, is that of martyrs, suicide teams, or kamikaze pilots, who are willing to give up their life in order to promote the spread of a meme: a religion, an ideology or a nation (i.e. a group defined by a common culture or ideology). In that case, the loss of one or a few carriers is compensated by the increased chances of survival for the other carriers or for the meme itself. For example, the suicide of an individual may attract the attention of other individuals to the meme he is carrying, and thus facilitate its spreading. A well-known example is Jan Palach, the Czech student who put himself to fire in order to protest the Soviet suppression of the "Prague Spring". In this case the meme would be the Czech version of "socialism with a human face".
Reference: Heylighen F. (1992) : "Selfish
Memes and the Evolution of Cooperation", Journal of Ideas , Vol.
2, #4, pp 77-84.