The rise of the farming lineages

There’s an open access paper/preprint on Y chromosomal lineages that just came out, A calibrated human Y-chromosomal phylogeny based on resequencing. Since it is open access you can read the whole thing (it’s short). Let me quote from the discussion:

Nevertheless, the rapid expansion of R1b (and possibly I1) in Europe contrasts with the less starlike expansion of E1b1a in Africa, which has been associated with the spread of farming, ironworking and Bantu languages in Africa over the last 5,000 years (Berniell-Lee et al. 2009). Both R1b and E1b1a samples are from a mixture of indigenous donors (from Europe and Africa, respectively) and admixed American donors, so sampling strategy does not provide an obvious explanation for the difference. Instead, the different phylogenetic structure, with far more resolution of the individual E1a1a branches, may reflect expansion starting from a larger and more diverse population, and thus retaining more ancestral diversity.

R1b is the most common haplogroup in Western Europe. This group places its growth 4-13,000 years ago. That suggests to them a Neolithic expansion. I am moderately confident in this number because ancient DNA extraction has not found much R1b in Europe 5-10,0000 years before the present, even though this lineage is present in proportions on the order of ~50% across much of Western Europe today. The contrast with the topology of E1b1a is striking as well, because we have some semi-historical evidence for the Bantu range expansion, and a great deal of autosomal genetic data which points to demographic replacement. A reasonable proxy for the pre-Bantu populations found in much of southern and eastern Africa persists in the form of Bushmen and Pygmies. This may not be the case in Europe. A more “starlike” phylogeny suggests explosive growth of this male lineage (this is the same topology of the Genghis Khan haplotype).

There are still reasonable debates as to the provenance of R1b. Was it present in appreciable frequencies in Western Europe before the end of the Ice Age? Or did it arrive with Middle Eastern farmers? Or perhaps Indo-Europeans? I think we can say with greater confidence that whatever its origin, the transition to agriculture was not one which sampled equally from the extant populations of Western Eurasia, but rather resulted in a winner-take-all dynamics as particular populations which small initial advantages expanded rapidly in numbers, and then compounded their advantages (e.g., more people means greater success in war, and more territorial expansion, which results in more land for demographic expansion). For some plausible reasons of human behavioral ecology it seems that this tendency toward winner-take-all would be most manifest in the Y chromosomal lineages.

It is common to speak of our “Paleolithic minds,” and the fact that most of our existence as a species has been as hunter-gatherers in an Ice Age landscape. But it is important to remember that the transition to the Holocene resulted in a radical reordering of the phylogeography of the human species, and perhaps even of our range of phenotypic variation.

H/T Dienekes

Source: Discover Magazine – Gene Expression