Memes vertically transmitted
A number of memes are transmitted in the population entirely or primarily from parents to offspring, i.e. via the same direction pathway as genes. As a consequence, together with the successful meme, i.e. with a meme that increases the inclusive fitness of its bearer, the genes that the bearers of the particular gene have in their genome can also spread in the population. However, this can happen only if the bearers of the relevant meme do not reproduce with individuals that do not carry the particular meme. This is generally a rather difficult condition to fulfill, so that ideally this situation can probably occur only for the spreading of the already mentioned meme for killing heathens. However, for a certain structure of the population and means of transmitting memes and genes, the progress of biological evolution can also be affected by cultural evolution when the bearers of the various memes reproduce together. In studies of the genetic polymorphism in four types of cetaceans, it was, for example, found that the mitochondrial DNA of each of the species is practically identical in the entire area (Whitehead 1998; Whitehead 1999). Similar to most other species of animals, here also the mitochondrial DNA is inherited only from the mother and is practically not subject to genetic recombination. From the viewpoint of population structure, these were matrilinear species in all cases, i.e. species in which the offspring remain in the original herd, while adult males visit other herds for short periods for the purpose of mating. As a result of this type of population structure, memes will also be inherited in the same way as mitochondrial DNA, i.e. down the maternal line. It is known that very intense cultural evolution occurs in cetaceans and the individual herds differ substantially, for example, in the means of obtaining food; the members of a single species catch completely different food in various areas and use very different hunting techniques (Rendell & Whitehead 2001). In some cases, vary rapid spreading of a new pattern of behavior has been observed, for example new hunting techniques within the entire area of occurrence of a particular species (Fig. XVII.7). The authors of the relevant molecular biological studies assume that the particular mitochondrial DNA variant spreads together with the spreading of the biologically successful meme, i.e. the meme increasing the fitness of its bearer, and that it finally replaced all the other variants in the gene pool of the species.