I-Y33765 and other Baltic Sea branches of I-Y4252

As at January 2022 FTDNA's Block Tree contained twenty branches immediately downstream of I-Y4252.  Similarly the YFull Tree v.9.05 contains sixteen clades at this position.  Bernie Cullen has written (2020) that "I-Y4252 had a rapid "star-like" expansion" and the number of "rays" emanating from this particular star have increased steadily since the discovery of I-Y4252 in 2014.  This trend will very likely continue as the number of Y4252 (+) men who have Next Generation Sequencing (NGS) results increase.  

It seems to me this burst of branching must indicate a period of enhanced reproductive success for the early group of I-Y4252 men.  Based on NGS results YFull date this phylogenetic expansion to about 2000ybp and it is worth noting that this makes it approximately concurrent with the geographical expansion of Germanic tribes in northern Europe which itself was triggered by social pressures and technological changes that developed within their society about this time. The modern incidence of I-Y4252 which is illustrated by the Phylogeographer Y Heatmap (Figure 1) shows that haplogroup is today distributed throughout the British Isles and across north-west Europe and southern Sweden, with two outliers centred on Dalmatia in the south and Lapland in northern Finland.  Again, this extended geographic spread within such a recent haplogroup suggests to me that the original ancestral cohort were able to migrate easily and that their descendants were comparatively successful within the environments they colonized.

 

Figure 1: Modern incidence of I-Y4252 in Europe (source:https://phylogeographer.com/scripts/heatmap.php ) 

Seven of these I-Y4252 clades contain samples with putative ancestral origins in areas that surround the Baltic Sea and in each case the branch has also recorded positive results from England (Table 1 and Figure 2).  

Table 1: Baltic Clades downstream of I-Y4252 as at January, 2022.  The "SNP" column shows the date at which the SNP that defines the clade was discovered.  The "Baltic Sample" column shows the YFull ID of men whose earliest documented direct-male ancestor lived near the Baltic Sea and the NGS test they have used.

In defining these Baltic clades I have included those branches which contain a sample with an ancestral location that is approximately within a distance of 200km (125 miles) of the shoreline of the Baltic Sea and also that contains a sample whose ancestral location is within England. I have used this methodology because it seems to me these several examples of geographically discrete, shared Y-DNA, support the idea of historical contacts between the Baltic Sea region and England.  

 

Figure 2: Distribution of the earliest known locations for the seven Baltic clades within I-Y4252

The areas bordering the Baltic Sea where I-Y4252 clades have been identified are extensive.  They stretch from north-western Germany and West Pomerania in the south, to Lapland on the shores of the Gulf of Bothnia in the north and from Denmark and southern Sweden in the west to north of St Petersburg at the eastern extremity of the Gulf of Finland.  It also seems to me that such an extensive distribution must reflect the importance of the sophisticated maritime culture that established long-distance trading contacts throughout the Baltic region during the Scandinavian bronze and early iron ages.

Each of these clades has a TMRCA during the first millennium (160 AD to 870AD) and so it would seem reasonable to conclude that their geographic distribution may be an echo of the contacts between England and the various parts of Scandinavia that occurred during the Dark Ages.   An exception to this is the I-FGC56815 branch (see Table 1) in which the clade that contains a supposed Baltic sample, I-FGC56855 (I-Y131221), has a significantly later TMRCA during the sixteenth century and consequently would seem to represent much later interactions.  

Poznik et al. (2016) have demonstrated that "at times of known migrations and technological innovations" the phylogeny of the Y chromosome contains several independent bursts or rapid expansions of male numbers and these authors suggest this is because "privileged male lineages could undergo preferential amplification for generations".  In a similar manner, Balaresque et al. (2015) observed that in Asian pastoral nomads Y-chromosome descent clusters may be associated with a greater ease of transmission of human Y-chromosomes through time and space as a result of gaining the skill to use horses for transport.  

It seems to me that an analogous burst of Y-chromosome mutations downstream of I-L233 happened during the Iron Age when Germanic tribes migrated out of Scandinavia concurrent with their development of an iron-riveted, clinker-built ship technology that facilitated swift movement on water over very considerable distances.  As a result, rivers, lakes, coastal voyages and even passage across open sea created well established routes by which their Y haplogroups became distributed throughout Europe.  Of special significance were the trans North Sea  routes that linked the British Isles and Scandinavia.

In addition it is worth noting that these demographic movements involved pagan tribal groups typified by the Anglo Saxons and Vikings who had a warrior, "raiding and trading" culture that radiated from communities bordering the Baltic sea.  In these groups social hierarchy tended to foster powerful male elites that practiced both polygamy and concubinage. It seems reasonable to think that these practices would further favour the proliferation and accelerated mutation of their Y-DNA.  Hence it may not be too surprising that we find so many Baltic clades within I-Y4252. 

Woolf (2015) suggests, based on archaeological evidence, that the development of the iron-rivet, clinker built ship technology was centered in Scania (southern Sweden) and Denmark.  The earliest surviving example of a Germanic vessel using the clinker technique comes from Nydam Moss, an archaeological site on the eastern side of the Danish peninsula just north of the modern border with Germany.  It dates from 320-350AD.   At Vendal and Valsgarde in the Swedish province of Uppland and in England at Sutton Hoo and Snape in Suffolk and at Sarre in Kent, sixth and seventh century ship burials have been excavated.  Those examples from Suffolk and Kent provide confirmation that the English "Saxon Shore" had extensive interactions with Scandinavia from 500-600AD (Brookes, 2007).  In this connection the ship burials at Gunnerstad, Gamleby, Tjust, Sweden, are worth mentioning as all four Swedish men derived for I-Y33765 have genealogy linking them to the surrounding area.

Figure 3: Proportions of major coin types from the 8th to 12th century found in countries bordering the Baltic Sea.  This illustration is based on data from Table 1, page 9, Talvio (2002).

Further archaeological evidence for contacts between England and the lands of the Baltic and Nordic regions is provided by coin finds (Talvio, 2002).  Interestingly, by comparing Figures 2 and 3, you will see that the proportion of English coins found in countries surrounding the Baltic Sea is higher in those areas where the Baltic clades observed downstream of I-Y4252 have also been recorded.  This would seem to support the idea that these areas had more contact with England during the Dark  Ages.  In 2008, a hoard of coins was found at Hellero, Vastra Ed, Tjust (Palm,2008).  This Swedish archaeological site is again close to the area where all four I-Y33765 Swedish men have documented direct-line male ancestry.  All the English coins in that hoard were made by mints operating in southern England at the end of the first millenium; in other words, in a similar area to where men on the English arm of I-Y33765 have their medieval ancestry.  

So, based on archaeological evidence, Viking Age contact can be substantiated that would inevitably introduce Y-DNA haplotypes from the Baltic region into England. The Baltic clades that proliferated downstream of I-Y4252  are examples of this process.     

 References

Balaresque, P. et al. (2015) Y-chromosome descent clusters and male differential reproductive success: Young lineage expansions dominate Asian pastoral nomadic populations. European Journal of Human Genetics 23, 1413-1422

Brookes, S. (2007) Boat-rivets in Graves in pre-Viking Kent: Reassessing Anglo-Saxon Boat-burial Traditions. Medieval Archaeology 51, 1-18

Cullen, B. (2020) Comment made in activity feed of I2a Project, FTDNA

Palm, V.,Nilsson, N.,Jonsson, K. (2008) Hellero - ytterligare en silverskatt fran Tjust, Smaland. Mynstudier, November 17-33

Poznik, G.D. et al.  (2016) Punctuated bursts in human male demography inferred from 1244 worldwide Y-chromosome sequences. Nat. Genet. 48(6), 593-599

Talvio, T (2002) Coins and coin finds in Finland AD 800-1200, Ed. Torsten Edgren, ISKOS, Finland.

Woolf, A. (2015) Sutton Hoo and Sweden Revisited In: The Long Seventh Century, Continuity and discontinuity in an age of transition. Ed.G.Alessandro. Peter Lang AG.