The enigmatic headless Romans from York

My dataset was recently enriched with six ancient individuals from Roman York, courtesy of Martiniano et al. 2016.

They were either gladiators or soldiers. Each one was decapitated. This may have been a coup de grâce or a burial rite. At least one, 3DRIF-26, was not native to Britian.

In fact, isotopic evidence suggests that he spent his childhood in a region with a hot and dry climate such as North Africa or the Levant. Moreover, his top matching population in terms of pairwise Identical-by-State (IBS) allele sharing are present-day Saudis (see here).

However, I thought it might be useful to revisit 3DRIF-26's genetic affinities after taking into account his non-trivial Sub-Saharan admixture. This can be done with qpAdm. The best ten models are listed below.

Please note that in the last model I had to use 3DRIF-26 as a mixture source for present-day Egyptians, because he has less Yoruba-related admixture than the Egyptians.

Anatolia_Neolithic 0.528
Caucasus_HG Kotias 0.379
Yoruba 0.093
chisq 2.813 tail prob 0.421347

Samaritan 0.940
Yoruba 0.060
chisq 3.706 tail prob 0.447229

Cypriot 0.915
Yoruba 0.085
chisq 4.564 tail prob 0.334981

Lebanese_Druze 0.933
Yoruba 0.067
chisq 5.961 tail prob 0.202081

BedouinB 0.998
Yoruba 0.002
chisq 6.311 tail prob 0.17709

Lebanese_Christian 0.929
Yoruba 0.071
chisq 6.660 tail prob 0.155006

Lebanese_Muslim 0.943
Yoruba 0.057
chisq 6.874 tail prob 0.142671

Druze 0.933
Yoruba 0.067
chisq 8.235 tail prob 0.0833513

Iraqi_Jew 0.924
Yoruba 0.076
chisq 8.443 tail prob 0.0766321

Egyptian
Roman_outlier 0.900
Yoruba 0.100
chisq 9.262 tail prob 0.0548746

I'd say these results provide rather convincing evidence that 3DRIF-26's West Eurasian ancestry is derived from the Levant. Moreover, his relatively high level of Sub-Saharan admixture suggests that he came from the southern Levant or perhaps a nearby region, like the Sinai Peninsula.

Interestingly, the best models feature a couple of religious minorities (Samaritans and Lebanese Druze), an island population (Cypriots), and a fairly unique group in terms of genetic structure from Israel's Negev Desert (BedouinB). This suggests that 3DRIF-26 may have belonged to a similar religious or geographic isolate population, or, alternatively, that most of the Levant has experienced significant genetic shifts since he was alive.

The rest of the headless Romans were, in all likelihood, born and raised in or near Britain. However, two of the individuals, 3DRIF-16 and 6DRIF-3, show elevated IBS affinity to Lithuanians and Poles. At the same time, they both belong to Y-chromosome haplogroup R1b-U106 (aka M405), which is a marker generally thought to have arrived in Britain with Anglo-Saxons and Scandinavians. This might be a coincidence, but probably not.

D-stats confirm that they do show elevated Northeastern European affinity relative to the other three Romans. Only one of the Z-scores is statistically significant (>3), but most of the others would probably also reach significance with more SNPs and higher quality sequences.

My guess is that 3DRIF-16 and 6DRIF-3 were Britons of mixed origin, with recent ancestry from Scandinavia and/or East Central Europe. Indeed, they can be modeled with qpAdm as part Swedish and Polish.

England_Roman 0.869
Swedish 0.131
chisq 1.784 tail prob 0.775339

England_Roman 0.884
Polish 0.116
chisq 1.971 tail prob 0.741124

Data source and citation...

Martiniano, R. et al. Genomic signals of migration and continuity in Britain before the Anglo-Saxons. Nat. Commun. 7:10326 doi: 10.1038/ncomms10326 (2016).