Estimation of the geo-ethnic origin of Y-DNA in Belgium
History is complicated, and migrations have often come from similar regions. So we may never know the proportion of Y-DNA that came directly from Italy during Roman times, as opposed from Gaul/France or southern Germany. It's impossible at present to distinguish between a G2a or T that came from the Near East to Belgium via the Neolithic farmer migration from the Balkans, one that came from Roman Italy, and one that came 200 years ago from France. We also can't know if a Belgian R1a is descended from Scandinavia, Eastern Europe, Greece or if that R1a has been in Belgium since the Corded Ware period. I will nevertheless attempt to give the maximum likelihood for the traditional ancient ethnic groups : Germanic, Celtic, Roman, and Neolithic farmers.
Germanic Y-DNA
The Germanic group is the easiest to identify because it has the most distinctive haplogroups. It is totally possible that Germanic tribes had a few "foreign" haplogroups among them by the time they invaded the Roman Empire and settled in Belgium. I will disregard them to simplify the task (and because anyway there is absolutely no way of knowing until ancient Germanic skeletons are tested). The following haplogroups in Belgium can be considered the result of Germanic migrations :
- I1 (12.5%)
- R1b-U106 (26%)
It is usually considered that I2b is also Germanic. But as it is in fact the descendants of Paleolithic hunter-gatherers, this haplogroup could have been present in Belgium for much longer. I have seen Belgian I2b STR haplotypes with no close match anywhere else, so they are unlikely to be a recent split from northern Germany.
R1a is even more complex due to its very wide geographic spread and few subclades. I find it strange that only 3.75% of R1a is found in Belgium. That's about what could be expected from the Corded-Ware settlement, but that leaves no place from later Germanic migration. Proportionally to I1 and R1b-U106, there should be at least an additional 4% (unless different Germanic tribes had very different frequencies). Or it could be that the R1a Indo-Europeans of the Corded Ware never crossed the Rhine, and therefore all the R1a in Belgium is of later Germanic origin. I think that this latter hypothesis is the most likely.
The last possible Germanic component would be the other clades of R1b than U106. I would exclude S28, SRY2627 and M343 because they are too rare in Germanic countries. But some P312, P310 and M269 could be Germanic.
I estimate that the minimum percentage of Germanic lineages in Brabant is :
12.5% + 26% + 3.75% = 42.25%
The maximum would be around 62%, depending on the actual number of I2b and other R1b of Germanic origin. 48% seems a reasonable estimate.
Italo-Celtic Y-DNA
The Celtic group is hard to define. The original Celtic speakers would normally be the Indo-European R1b. The question is whether the Indo-European Celts really intermingled with the locals, or whether they remained a separate social group throughout the age of Celtic culture, until the Roman conquest. The Celtic ruling class was patrilineal, so it is easy to imagine the Celtic aristocracy being made up primarily of R1b lineages.
The Celts lived in towns and owned slaves, probably taken from the aboriginal population. But what exactly happened to the Pre-Celtic farmers and megaliths builders when the Proto-Italo-Celts settled in Central Europe about 4000 years ago ? Indigenous paternal lineages suffered a considerable set back over time. Pre-Celtic I2, J2b, E-V13, G2a and T all together only account for 10 to 15% of the modern Belgian Y lineages (depending if we include I2b or not), so only a third to half of the supposed R1b lineages of Italo-Celtic origin. As all those pre-Celtic lineages are also found in France, southern Germany and Italy, it is not even certain that they are the continuity of the lineages found on the Belgian territory, or a later repopulation that came during the La Tène or Roman period.
Did the Neolithic farmers keep farming on the side for their new Celtic rulers in their oppida, or did they become completely Celticised and integrated ? Both Celtic and Roman nobility were pretty exclusive. Nobles were the only ones allowed to become warriors, just like in medieval times. Nobles stayed in the forts or towns, and farmers in their villages. The Celtic aristocracy will surely have taken beautiful wives or concubines among the local farmers, progressively mixing autosomal DNA. Y-chromosomes, however, would have been preserved.
With this in mind, true Celtic lineages (Indo-European aristocracy) would be the R1b-P312 lineages and its subclades, i.e. 32% of the population (a small percentage of these lineages could be Germanic though).
Only a few centuries separate the La Tène expansion to Belgium from the Roman conquest. It is therefore difficult to determine which of the present-day haplogroups are descended from ancient Belgae and which are Roman. The only percentage I can give is the Gallo-Roman (or Belgo-Italic) admixture. Roman in this case means Northern and Central Italian around 2000 years ago. Southern Italians being mostly of Greek and Phoenician descent, I will create another category.
Near-Eastern Y-DNA
Neolithic farmers are also ultimately from the Near East, but they came to Europe much earlier, and via a very different route through the Balkans and the Danube basin. Their autosomal admixture would be quite different from the southern Italians and Greeks of classical times. That is why I insist on separating the two groups.
Most J2a, J1, L and other E subclades than V13 are probably of Etruscan, Greek, Phoenician or southern Italian origin rather than northern Italian or Central European. That represents about 7.5% of the population. Add to that the 4.5% of R1b-M343, which could also be Greco-Anatolian or southern Italian.
In conclusion, up to 12% of the Brabantine Y-DNA could be of Greek or Levantine origin, in addition to the 7.5% already counted under "Neolithic farmer". That's nearly 20% of Near-Eastern Y-DNA, a bit more than I expected.
