Genetic and linguistic diversity: Global distribution and implications for prehistory

Whilst some have claimed that languages and genes evolve in tandem within the human population, data on genetic diversity show that this is not the generally the case. Human genetic diversity is greatest within, and reduces with distance from, Africa. This pattern arose from serial founder effects as an African source population colonised the rest of the globe. Diversity of language families is rather low in African and Eurasia, and highest in Oceania and the Americas. I suggest that this is because language-family diversity is most heavily conditioned by homogenisation associated with agricultural expansions in the Holocene. Such expansions affected more of the land masses of Africa and Eurasia than of Oceania or the Americas. I argue that the different patterns of diversity found in genes and languages are to be expected, since their mechanisms of transmission are so different, with language fast to mutate but potentially slow to diffuse, and genes slow to mutate but fast to diffuse.