Friday, November 5, 2010

Tuscans: Can we guess their origin?

A Cypriot Shepherd

Close examination of the Tuscan results from Dienekes' k=10 ADMIXTURE run revels the familiar Fertile Crescent signature.  It's buried, but in what?

For now, let's assume that the source of the Southwest Asian component in Tuscans originates wholly in the Eastern Mediterranean.   Moreover, let's choose the nearest known Fertile Crescent population, Cypriots.  That may not be the case, but we can revisit that assumption later.

We can quickly calculate that since Cypriots have a 22.8% Southwest component and Tuscans have a 7.7% Southwest component, Tuscans should be composed of 7.7/22.8 = 0.338 Cypriots and 0.662 of a Mystery Composite.

We know that the Mystery Composite must have North European, South European and West Asian components.  Taking a guess at what Mystery Composite is composed of, we let West Asians(column 1), range from 5% to 15%.  We let South Europeans(column 3) range from 45% to 50% and Northern Europeans(column 7) vary from 0.35% to 50%, as follows:

Table of Population Subcomponents 1 to 10
Guess for "Mystery Composite"
Adjusted for "Cypriot" Fertile Crescent Contribution

We now plot Tuscans against 0.338 Cypriots + 0.662 Mystery(1 to 6):

In the stacked bar graph, Tuscans are presented on the left of each two bar set.  There are six bar sets, represented by variations 1 to 6 in the table.   The right bar of each set is 0.338 Cypriots + 0.662 Mystery.  In the graph, variation 1 and 4 both match the Tuscan West Asian subcomponent.

Averaging 1 with 4, one can very quickly see that the solution for Mystery is

[0.15  0  0.475  0  0  0  0.375  0  0  0]

15% West Asian, 47.5% Southern European and 37.5% Northern European.

It would be unlikely that Mystery is the result of a single admixture event, but rather is the result of Neolithic, Bronze Age and Iron Age gene flow between Tuscany, Sardinia and peoples arriving from the north.

Here, we've assumed that it is Cypriots who migrated to Tuscany.  In the next post, we'll see what happens if we assume that Syria was the source of the Tuscan Fertile Crescent component.

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