I-Y33765 and early maritime culture in the Baltic

Four Swedish men with seventeenth or eighteenth century direct-line male ancestry from the harads of Tjust or Kinda, Småland are derived for the I-Y33765 SNP and share a varying number of downstream (more recent) mutations.  Apart from this genetic similarity there is no documented genealogical connection between these men.   The grouping of their four derived (+) results in such close proximity suggests that the Tjust region might be considered the ancestral "homeland" of the I-Y33765 clade.

The eastern boundary of Tjust is formed by the Baltic Sea and here it's coast is characterized by an archipelago with elongated bays, that at several places extend deep into the interior of the region.  Since the end of the last ice age there has been considerable geological "uplift" along much of the eastern seaboard of Sweden (Passe & Daniels, 2015) and in the area of Tjust since the Vendel period (AD550-800) this elevation of the shore level has been by two or three metres.  Hence, at the time the Y33765 mutation formed (circa 670AD), inlets, rivers and streams would have been navigable further inland.  During the Vendel and Viking periods the major bays of Gamleby Viken and Gudingen and the streams entering them would have provided perfect navigable access to the hinterland around the present day settlements of Gamleby & Lofta.

This was also the case during the early Iron Age and Bronze Age and the Tjust coast has many examples of Bronze age rock carvings that demonstrate the familiarity of those living there with boat building, sea faring and navigation.  At Casimirsborg in Gamleby parish in 2010 an outcrop of rock was discovered that shows one of the largest groups of Bronze Age ship images found anywhere in Scandinavia.  It contains representations of over a hundred engraved ships (Goldhahn, 2011).  When the images were made in the middle part of the Bronze Age the rock outcrop on which they are carved lay near the eastern shoreline of Gamleby Viken in a natural harbour (Broström, 2011).

Bronze age ships depicted in rock art at Carimirsborg, Gamleby parish, Tjust, Sweden

Similar rock art images of ships are found in other coastal areas across the Baltic and together these demonstrate that a maritime culture existed around its shores from an early date.  Archaeologists consider this shared culture reflects a Bronze Age coastal trading network.  A detailed study of the archaeology of this network (Wehlin, 2013) has identified Gamleby Viken as one of several "nodes" on the east coast of Sweden that connected the western Baltic to Gotland, Mälaren and the Gulf of Finland in the east (see map).  Wehlin terms this network of trade routes and shared maritime culture around the eastern Baltic as a "Maritorium".

Baltic trade routes.  The route along the east coast of Sweden, which connected the western Baltic to the Gulf of Finland was in use from the Bronze Age.  The extensive bays of Gamleby Viken and Gudingen are a strategic anchorage on this route, north of Oland and opposite Visby and facing the eastern Baltic (cross symbols show ancestral locations for I-Y33765  men)

It seems quite plausible that the technically advanced Bronze Age shipbuilding implicit in such an extensive network would develop into the robust and innovative Scandinavian ship technology of the Iron Age based on broad, shallow drafted, lapstrake hulls (clinker boarded), in which the strakes (boards) were joined together with iron nails riveted through iron roves (washers), and masts with a single rectangular sail.  This sophisticated Scandinavian ship building revolution allowed "Northmen" from Denmark, Norway and Sweden to trade, pillage and explore into distant seas and rivers of the then known world. In the Baltic many of the trading routes that were established in the Bronze Age persist through to the late Viking Age and beyond (see map above).  So for centuries this maritime network would have distributed the genetics of Scandinavian coastal communities, along with their produce and goods, throughout the inland sea and beyond. 

The essence of Iron Age Scandinavian ship technology: a handmade iron ship rivet and rove washer (left); ship rivets from the Sutton Hoo ship burial (middle); ship rivets joining the strakes on the Nydam iron age boat (right).

Clear archaeological evidence that this Iron Age maritime culture was active in the Gamleby district contemporary with the formation of the I-Y33765 SNP has already been recorded. The cremation boat burial at Gunnerstad contained iron ship rivets indicating that the boat used was of clinker boarded design and the scorching of stones within the mound suggested it's length was about 5m.  This size would make it suitable for rivers and protected routes following the coastline. The burial has been dated to the beginning of the 6th century AD (Palm, 2017) during the Vendel Period and at that date such a craft may have just had oars rather than a mast and rectangular sail   Also, between the bay of Gamleby Viken and the inland waters of  Dynestadsjön the remains of a Viking period “pole barrage” has been radio-carbon dated to 1030 +/- 30ybp. (Palm & Rönnby. 2018).  The structure is submerged within the narrow channel of Dynestadviken at a place called Stäket.  Archaeological surveys of the site are ongoing but marine archaeologist Johan Rönnby of  Södertörn University / MARIS has said "I would not be surprised if there is a Viking ship down there somewhere because it was quite common to use old boats when constructing pole blockages".  At the Skuldelev defensive blockage in the Roskilde Fjord, Denmark, six old ships were sunk for this purpose between 1070 and 1140AD. These Skuldelev wrecks were excavated by Danish archaeologists in the late 1950's.  The pole blockage at Stäket probably indicates that the Dynestadsjön pool was used as a harbour during the Viking Age. If so, this is evidence that the hinterland of the nearby Husa "central place" was connected to the Baltic trading network at this time.

Within the past month the result of a major, six year study into the population genomics of the Viking World has been published.  The authors (Margaryan et al., 2020) extracted genomic DNA from 442 ancient humans, mostly from Viking age burials (142 Viking age samples from Sweden) and compared them with genomic samples from modern populations.  Their findings confirmed previous conclusions based on medieval documentary sources and on archaeology; that Vikings with Danish ancestry mainly moved west to England, those with Norwegian ancestry traveled to Iceland, Greenland, Ireland and the Isle of Man, while the eastward expansion and exploration of the rivers of Russia and eastern Europe involved Vikings who were mainly from Sweden.  However they noted "we also see evidence of individuals with ancient Swedish and Finnish ancestry in the westernmost fringes of Europe".  This comment seems compatible with the evidence available from present results for the I-Y33765 clade which appears to have migrated from south eastern Sweden to south western England. These authors also report that in most of Viking Age Scandinavia the distinct regional populations show little or no evidence of genetic mixing.  However they found greater genetic diversity in "a few cosmopolitan centers to the south" in southern Sweden (notably Oland and Gotland) and Denmark.  They interpret this as being "consistent with a limited number of sea routes between different Scandinavian areas and beyond".  

Just how to estimate when I-Y33765 is most likely to have made its journey from Scandinavia to England is an interesting puzzle. As mentioned earlier, historic sources and archaeology strongly suggest that earlier Swedish Viking voyages both for trade or plunder were typically to the east. Maritime trade routes connected to Tjust would seem to facilitate travel in that direction.  Consequently, it does not seem unreasonable to conjecture that, as the I-Y33765 SNP formed circa 670AD, during the three hundred years following its formation any chap carrying that mutation would naturally seek his fortune to the east. Hence it maybe that in the future, when more men have their Y-DNA tested, descendant lineages of I-Y33765 will be identified in Estonia, Belarus or Ukraine.  

Rune stone Sm101 in the parish of Nävelsjö, Småland: The runic inscription is translated as "Gunnkel placed this stone in memory of Gunnar, his father, Rode's son. Helge laid him, his brother, in a stone coffin in Bath in England".  Sweyn Forkbeard's followers were at Bath, Somerset in 1013.

It was only when the flow of silver dirhams from the Middle East decreased in the latter quarter of the tenth century that Swedish adventurers began to look elsewhere for opportunities and, as a result, joined the ambitious Danish kings on their manoeuvres to the west,  in England. Although rune stones are not dated, the majority of those in Sweden that refer to men who traveled to, or who died in, England seem to relate to the period at the very end of the 10th and beginning of the 11th centuries when English silver geld payments were at their maximum.  It seems to me very likely that during these few years or the decades immediately after, between say Sweyn Forkbeards first attacks on England in the early 990's and his grandson Hathacnut's death in 1042, the I-Y33765 haplogroup somehow "found it's way" from Tjust to north Somerset.   And as evidence that this may not be too fanciful an idea a Viking Age rune stone in Småland, in the parish of Nävelsjö (Sm101), is a memorial to a man named Gunnar who made almost exactly the same journey during that period. He died and "Helge laid him, his brother, in a stone coffin in Bath in England".  Nävelsjö is about 100km south west from Tjust and the city of Bath is in north Somerset about 15km east of the parishes where the ancestors of our English I-Y33765 men were living in the eighteenth century. 

References

Broström, S.G. (2011) Skålgropsfat, skeppshäll och solvagn : nyfunna hällbilder vid Casimirsborg i Tjust vid norra Smålandskusten, Fornvännen, Journal of Swedish Antiquarian Research, 106, 54-57

Goldhahn, J. (2011) Törnsfall 107 – hällbilder vid ett röse och ett röse med hällbilder, Kalmar Studies in Archaeology VIII, Linnéuniversitetet, Kalmar

Margaryan, A., Lawson, D., Sikora, M. et al. (2020) Population genomics of the Viking world. Nature 585, 390-396 

Palm,V., Rönnby,J. (2018) Stäket vid Valstad, Gamleby socken, Stiftelsen Västerviks museum

Passe, T., Daniels, J. (2015) Past shore-level and sea-level displacements, Geological Survey of Sweden

Wehlin, J. (2013)  Östersjöns skeppssättningar - monument och mötesplatser under yngre bronsålder,  GOTARC Serie B. Gothenburg Archaeological Theses 59