Over at A Replicated Typo they are talking about a short paper in Science, Mother Tongue and Y Chromosomes. In it Peter Forster and Colin Renfrew observe that “A correlation is emerging that suggests language change in an already-populated region may require a minimum proportion of immigrant males, as reflected in Y-chromosome DNA types.” But there’s a catch: they don’t calculate a correlation in the paper. Rather, they’re making a descriptive verbal observation. This observation seems plausible on the face of it. In addition to the examples offered, one can add the Latin American case, where mestizo populations tend to have European Y chromosomal profiles and indigenous mtDNA.
In one of the more nuanced instances cited by Renfrew and Forster they note that though there is a fair penetration of both Austronesian mtDNA and Y chromosomes amongst Austronesian speaking inhabitants of New Guinea, Austronesian Y chromosomes are nearly absent from those populations which speak Papuan. In other words, the inference is that the native indigenous male elite perpetuated the Papuan language! I think the key issue here is social dominance, and the role of male cultural units. This is clear when you have a group like African Americans. Though mostly West African in ancestry this ethnic group clearly has ~20% European ancestry, mostly mediated through European males. This is simply a function of the social dominance of European males in relation to African males. And, it may be telling that African Americans are an English speaking Christian population, albeit with their own distinctive accent.
In the paper the authors note:
…It may be that during colonization episodes by emigrating agriculturalists, men generally outnumbered women in the pioneer colonizing groups and took wives from the local community. When the parents have different linguistic backgrounds, it may often be the language of the father that is dominant within the family group….
There is certainly some truth to this. But what I think that this narrative misses are the coarser and larger scale social units which expansive male cultural communities operate through. The spread of European males in Latin America was not uncoordinated. Often small groups of males decapitated indigenous male power elites, sometimes literally! Long distance travel, such as what the Austronesians engaged in, almost certainly must have entailed a minimal level of political and ideological commitment. They cite the example of the Genghis Khan haplotype, but that wasn’t perpetuated through a process of gradual demic expansion.