Dawkins suggests that it is memes and passed along through the brain some how, but that is pure conjecture and there is no empirical evidence as far as I know.
It's been some time since I read the 'Selfish Gene' but as I recall Dawkins' concept of a 'meme' was not some sort of genetically inherited personality trait, but the opposite: a mental construct, ideas and/or concepts we had picked up via our interactions with society. Things like changing fashions, childrens' playground crazes etc. He even gave religion as an example of a (in his opinion, harmful) meme which was good at persisting and replicating (perhaps without any direct benefit to the host!)
Although some aspects of population genetics might be applicable to the meme concept (they can mutate, for example: people can add to an idea, or recall gossip imperfectly when passing it on), Dawkins' point was actually that human society and culture could not be explained completely by genetics - through language and more recently written records, humans have other ways of passing behaviour on to later generations. Which just goes to show, even the Ultimate Materialistic Bogeyman realises the limits of reductionism...
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