The main finding of the authors is that haplogroup J was not carried by a single advance from the Middle East into Europe. Rather, at least two expansions can be detected, a "Neolithic" one and a "Greek" one:
In summary, our data are in agreement with a major discontinuity for the peopling of southern Europe. Here, haplogroup J constitutes not only the signature of a single wave-of-advance from the Levant but, to a greater extent, also of the expansion of the Greek world, with an accompanying novel quota of genetic variation produced during its demographic growth. In the analysis by Cavalli-Sforza et al. (1994), the two peopling contributions can be distinguished, as they are caught in the first and the fourth principal component, respectively, but the relevance of the latter may have been underestimated. The two processes, widely spaced in time, are associated with dramatically different travel technologies. This implies that, in the central and west Mediterranean, the entry of J chromosomes may have occurred mainly by sea, i.e., in the south–east of both Spain and Italy.
Human Genetics (online first)
Y chromosomal haplogroup J as a signature of the post-neolithic colonization of Europe
F. Di Giacomo et al.
Abstract In order to attain a finer reconstruction of the peopling of southern and central-eastern Europe from the Levant, we determined the frequencies of eight lineages internal to the Y chromosomal haplogroup J, defined by biallelic markers, in 22 population samples obtained with a fine-grained sampling scheme. Our results partially resolve a major multifurcation of lineages within the haplogroup. Analyses of molecular variance show that the area covered by haplogroup J dispersal is characterized by a significant degree of molecular radiation for unique event polymorphisms within the haplogroup, with a higher incidence of the most derived sub-haplogroups on the northern Mediterranean coast, from Turkey westward; here, J diversity is not simply a subset of that present in the area in which this haplogroup first originated. Dating estimates, based on simple tandem repeat loci (STR) diversity within each lineage, confirmed the presence of a major population structuring at the time of spread of haplogroup J in Europe and a punctuation in the peopling of this continent in the post-Neolithic, compatible with the expansion of the Greek world. We also present here, for the first time, a novel method for comparative dating of lineages, free of assumptions of STR mutation rates.