MemesWhat about cultural symbionts? Numerous people have speculated that different cultural traditions historically lead to sharp divisions between human populations - though of course these days, culture appears to be having the opposite effect - of uniting the whole planet. One issue I address in my memetics book is whether the historical divisions could have been deep enough to result in reproductive isolation and speciation. We can see a number of what appear to be speciation events among our ancestors, though the sort of isolation that produced them is not always clear. Of course there's one particularly obvious speciation event - the one that divided us from chimps. Could that have been caused by a difference in cultural traditions?
It's long been speculated that bird song is a possible cultural mechanism for speciation.
A recent paper about speciation in killer whales proposes that learned cultural differences between ecologically divergent killer whale populations have resulted in sufficient reproductive isolation even in sympatry to lead to incipient speciation.
These kinds of thing promote the link between cultural symbionts and speciation. If sufficient evidence of cultural symbionts causing speciation arises from the study of other species, we are going to have to seriously consider the possibility that our ancestors were so divided by their memes that their populations became permanently divided.
RaftsIsland isolation represents one of the best-known speciation mechanisms. It is known that some species colonise islands using natural rafts as a form of based on oceanic dispersal. Interestingly, the ability to build rafts is largely a culturally-transmitted trait among humans. Rafting could easily have promoted geographic isolation on islands among our ancestors. Human use of rafts dates back at least 100,000 years. There's evidence that Homo Erectus migrated through the Indonesian archipelago using bamboo rafts. Many other primates have managed to hop around the planet on natural rafts long before that. Memes could have isolated some of our ancestors in more than one way.