A first look at the genome of the Tyrolean Iceman

Thanks to the publication of the Tyrolean Iceman's (reconstructed on the left) genome sequence, by Keller et al. (2012), I have been able to include him in a joint analysis with 2,671 other individuals, previously assembled for the K7b and K12b calculators of the Dodecad Project.

I have essentially repeated the unsupervised ADMIXTURE analysis from scratch, with two differences:

• The dataset now includes Oetzi, and
• The number of markers has been reduced to 44,435 by intersecting the 166,770 SNPs used in K7b/K12b with the SNPs available for Oetzi

I had predicted that Oetzi would turn out "Mediterranean" in his genomic profile, and the published analysis seems to have confirmed this by discovering that his closest modern kin are Sardinians, a Mediteranean population. Sardinians are usually modal for the various "Mediterranean", and "Atlantic_Med" components inferred by the Dodecad Project.

Thankfully, the ADMIXTURE analysis in both the K=7 and the K=12 case, resulted in the same solution as in K7b and K12b, despite the inclusion of Oetzi and the fact that a smaller number of markers were used. There are slight variations in the admixture proportions compared to the K7b/K12b numbers, and an expected increase in "noise levels" in the minor components, but the overall solution appears to be the same.

The results for Oetzi and the reference populations, including Dodecad populations with 5+ members are included in the spreadsheet.


Below, I will briefly comment on them.

K=7


Oetzi turns out to be 51.9% "Southern" and 43.1% "Atlantic_Baltic" in the K=7 analysis, with noise levels of the other components. The salient point is that he seems to be lacking the "West Asian" component, unlike most Europeans, except Basques and Sardinians, who have:

Basques: 27.6% "Southern" and 69.5% "Atlantic_Baltic"
Sardinians: 46.2% "Southern" and 52% "Atlantic_Baltic"

So, Oetzi does appear to be most Sardinian-like in this analysis, and indeed to be a little more "Southern" than extant Sardinians. This is consistent with Keller et al. (2012) which finds him to cluster with Sardinians and to be a bit more "southern" (in PCA space) than Sardinians.

K=12

Oetzi turns out to be 57.7% "Atlantic_Med" and 22.3% "Caucasus" in this analysis. Once again, this makes him quite similar to Sardinians who are 64.9% "Atlantic_Med" and 21.3% "Caucasus". Two components are salient in their absence: the "Gedrosia" component which is present in non-Sardinian modern Italians, and the "North_European" component which is also present in the same.

Discussion


If we compare Oetzi with modern Europeans, he certainly appears to be most Sardinian-like. If we compare him to modern Italians (the samples N_Italian_D, North_Italian, as well as the neighboring Tuscan, TSI30, and C_Italian_D) populations, he appears to possess many of the same components (including Atlantic_Med, Caucasus, Southwest_Asian, and Northwest_African in non-trace quantities).

This of course does not indicate that Oetzi was of "mixed" ancestry, since ADMIXTURE components are but imperfect reflections of ancestral populations. It does, however, indicate that his profile consisted of many of the same elements found in Italy today, but in different proportions. Moreover, any additional or "exotic" ancestry in Oetzi cannot have existed in substantial amounts so as to render the inferred proportions (in terms of modern populations) nonsensical.

The three exceptions to this rule are the "West_Asian" component in K=7 and the "Gedrosia"/"North_European" components in K=12, which are conspicuous in their absence. And, given that all three of these have their present-day center of weight in more eastern longitudes, we can be fairly certain that present-day Italians have been affected by people from the east, by one or more routes.

This is, again, reasonable, and in agreement with the observation of Keller et al. (2012) -pictured on the left- that the Iceman occupies a "western"/"southern" position relative to modern Italians, and is consistent with the idea that modern Italians were formed by an eastward shift (in the case of more southern Italians) and a northeastward shift (in the case of more northern Italians).

We can have near-absolute certainty that a "North European" element was present in northernmost Italy by at least the first half of the first millennium BC, the time of the Hallstatt culture of Central Europe and of historical references about the arrival of Celts in Cisalpine Gaul. Oetzi is dated to the latter half of the 4th millennium BC. Hence, there is an intervening period of about 2.5k years between the two; it will be interesting to sample individuals from that time period to see when -within that time interval- the arrival of this trans-Alpine element occurred. It will also be very interesting to sample individuals from further north, east, and west, to ascertain the full spatial extent of "Oetzi-like" individuals during the early Copper Age.

Similarly, we can be certain that more "eastern" elements were present in Southern Italy by at least the time of the Greek colonization, which occurred at much the same time as the arrival of the Celts in the north. However, since all Italians are eastward shifted relative to Oetzi, even those from furthermost north, it is likely that the eastward shift of modern Italians preceded the historical colonization and that some of the myths preserved by Roman and Greek writers about eastern origins of various pre-archaic Greek and pre-Etruscan Italian peoples may hold an element of truth.

At present, we are disadvantaged by the fact that we are trying to place ancient individuals within a modern genetic landscape. Oetzi's genome suggests the fluidity of this landscape as we move into the past. Thankfully, it is all but certain that we will soon obtain full genome sequences from other prehistoric and historic individuals from different spots in space and time, so our understanding of how West Eurasians came to be is only bound to improve.