The spread of different languages in ancient times might seem like a difficult thing to track, but a big part of the story is actually hidden in our genes. Here's the twist: language change is a male-dominated phenomenon.
That might seem like a pretty big claim, so let's examine this a bit. First of all, how is it even possible to track language change using genetics? Basically, we can use certain genetic markers that remain unaltered as they are passed down from generation to generation to reconstruct the movements and origins of different populations. These genetic markers are gender-specific - the Y chromosome for males, mitochondrial DNA for women - which allowed Cambridge researchers Peter Forster and Colin Renfrew to focus on what role gender played in the transmission of language.
As it turns out, males are much more closely associated with language change. One of the best examples of this is the ancient spread of Polynesians into Melanesian territory, creating alternating pockets of Polynesian and Melanesian speaking regions along the New Guinea coast. Crucially, the level of Polynesian mitochondrial DNA in these areas is always about the same - 40% to 50% - regardless of which language is spoken. But the Polynesian Y chromosome is a different story - it's found almost exclusively in the Polynesian speaking areas, and barely at all in the Melanesian speaking regions.
But why is all this happening? To understand this, we need to remember that languages spread because people moved from place to place, and throughout human history men have generally enjoyed far greater mobility than women. In different instances, these males could be conquering warriors or immigrant farmers, but the basic fact remains the same - men could move to new regions in far greater numbers than women could. And when women did move, it wasn't always by choice - consider the case of Vikings kidnapping British women and taking them to Iceland. Under those circumstances, it's not exactly surprising that the language of Iceland isn't Old English.
Professor Renfrew adds:
"It may be that during colonisation episodes by emigrating agriculturalists, men generally outnumber women in the pioneering groups and take wives from the local community. When the parents have different linguistic backgrounds, it may often be the language of the father which is dominant within the family group."
There are also some basic biological facts to consider. Because they can't get pregnant, men are able to father multiple children by multiple mothers in far, far greater quantities than women realistically could. It's a simple enough point, but the effects can be profound - look at Genghis Khan, who legendarily fathered hundreds of children and whose Y-chromosome is now thought to be carried by 0.5% of the world's entire male population. All this means that a male immigrant will have far more chances to pass his language onto his genetic descendants than a woman would.
Dr. Forster notes that this is a somewhat surprising result, if nothing else because of one of the more popular phrases used to describe a native language:
"Whether in European, Indian, Chinese or other languages, the expression ‘mother tongue' and its concept is firmly embedded in popular imagination – perhaps this is the reason why for so many years the role of fathers, or more likely, specific groups of successful males, in determining prehistoric language switches has not been recognised by geneticists. Prehistoric women may have more readily adopted the language of immigrant males, particularly if these newcomers brought with them military prowess or a perceived higher status associated with farming or metalworking."
It's a fascinating result, and a not entirely pleasant reminder of how deep historical patterns can shape our linguistic and genetic inheritance today in ways that we're only now beginning to understand.