The flows and pulses of humanity

Dr. John Hawks points me to a review in BMC Biology, A question of scale: Human migrations writ large and small. It's short, and of interest for the citations themselves. This a field in flux. One point which I think needs to be emphasized in relation to migration parameters is that there are going to be two primary modes which this might play out, short range deme-to-deme contact, and long range cultural/genetic revolution (there is going to be a range between the two, but let us suppose that these are two modes in the distribution). The first case would involve the exchanges of individuals (voluntary or involuntary) between nearby groups. This is where the disjunction of the nature of inheritance between genes and culture comes into play. There are cases, such as in Iraq, where Indo-European (Kurdish languages) and Semitic (Arabic) speakers come into contact. The between group difference in speech is enormous, but it turns out that the genes are not really that different. In fact, Persian speakers from Khorasan, may be a genetic outgroup to Arabic & Persian speakers from western Iran, Kurdistan and Mesopotamia. Though on a macroscale linguistic and genetic trees may be similar because of geography, on a finer resolution the nature of language means that there's a much sharper linguistic than genetic distinction. But the second dynamic are cultural revolutions which produce demographic explosions and transformations. We have plenty of them of recent vintage. The rise of Europeans stands out, but the spread of Bantu dialects was probably concomitant with a genetic change across much of Africa, while Mongol Empire seems to have left a residue of ethno-genetic anomalies across Eurasia. These events seem to be more common in the recent historical period, likely because of the greater rate of cultural innovation, but the rise and spread of anatomically modern humans outside of Africa is arguably the first cultural/genetic explosion.