Nature | Vol 637 | 2 January 2025 | 125
(including one with ancestry related to Britain) are part of the majority 
strontium values, consistent with them having grown up locally. By 
contrast, the six most clearly non-local individuals based on the sta-
ble isotopes all have 50% or more EIA Scandinavian Peninsula-related 
ancestry, although three individuals with wholly EIA Scandinavian 
Peninsula-related ancestry also had local values. This suggests that 
the presence of central European-related ancestry was not a transient 
phenomenon, but an ancestry shift that occurred at some point after 
about 500 ce, the period to which individuals from the massacre site 
at Sandby Borg ringfort on Öland were dated; these individuals all have 
strictly EIA Scandinavian-related ancestry. Indeed, one hypothesis is 
that the massacre at Sandby Borg could represent conflict associated 
with movements of people that contributed to later ancestry change, 
although other scenarios are possible and further synthesis of biomo-
lecular and archaeological data is necessary to test this hypothesis.
Viking Age mobility into Scandinavia
Previous studies had suggested a major influx of ancestry related to 
Britain into Viking Age Scandinavia 6,7. Although we detect this ances-
try in some individuals (7 individuals in Norway, 14 in Denmark and 
14 in Sweden), including some individuals whose ancestry appears to 
be entirely derived from Iron Age Britain, its overall impact appears 
reduced compared with previous reports. Our analysis indicates a pro-
portionally larger impact of ancestry from Iron Age Britain in northern 
Norway, with southern Scandinavia predominantly influenced by 
continental central European ancestries (Fig.  4d). We hypothesize 
that our estimates of ancestry from Britain are reduced relative to 
previous studies because ancestry related to Britain and continen-
tal central Europe may have been indistinguishable. This could be 
due to a lack of statistical power to distinguish these closely related 
sources with standard methods, as well as through potential biases 
introduced by using modern surrogate populations that have since 
been influenced by later gene flow (such as gene flow into Britain). 
We illustrate this by replicating the analyses previously described 6,7 
(Extended Data Fig. 8).
Similarly, a previous study has suggested that individuals at sites such 
as Kärda in southern Sweden carried ancestry from southern Europe6. 
In our models, two Kärda individuals fit with central European-related 
ancestry, but none of the individuals has a substantial proportion of 
ancestry related to southern European sources (Extended Data Fig. 9). 
Instead, we detect ancestry from southern European sources in only 
three individuals from Scandinavia, and in relatively small propor -
tions (Fig. 4a).
Interestingly, we detect ancestry from Bronze and Iron Age sources 
from Eastern Europe (present-day Lithuania and Poland), concentrated 
in southeastern parts of Sweden, particularly the island of Gotland  
(14 individuals; Fig.  4a). This is consistent with previous genetic 
studies6,7. We find that this ancestry is enriched in male individuals 
(Extended Data Fig. 7d), suggesting male-biased mobility and/or burial. 
The closest match tends to be Roman Iron Age Lithuanian genomes 
associated with Balts, which would be consistent with mobility across 
the Baltic Sea, but we caution that the geographical representation of 
available genomes is still limited.
Viking Age expansion from Scandinavia
Traditionally, historical perspectives on what is now often referred 
to as the Viking diaspora placed an emphasis on the movements and 
settlements of population groups from various parts of Scandinavia67. 
Our explorative MDS analysis again indicates mixed ancestries related 
to the Scandinavian EIA, with regional differences that point to varied 
local admixture (Fig. 4e and Extended Data Fig. 10).