Jews Behind The Mountains

For the last year or so, I’ve been collecting Iberian, Hispanic, and Sephardic DNA matches. My goal: to map out the segments of my genome inherited from Jews who fled Spain and Portugal, trace them to specific branches of my family (most of whose paper trails run out in the early 19th century), and maybe, just maybe, establish connections to specific places on the Iberian Peninsula.

In my last post, I conjectured that deep analysis of my Y-chromosome subclade could help elucidate my direct male line’s path across the Mediterranean, into the proto-Ashkenazi community, and out to the Polish-Ukrainian border shtetl of Luboml. In all likelihood, this is the path of most of my ancestors. But Central and Eastern Europe have never held much appeal for me; by contrast, I speak Spanish and Portuguese, and have visited both Iberian countries more than once. Focusing on my minor Sephardic ancestry keeps things interesting, and allows me to work at a manageable scale.

With the help of Kevin Brook of, I’ve managed to validate 30 significant segments of Sephardic origin, with several others of lower confidence. Each of them matches at least a few Iberians or Latin American Hispanics, plus the usual boatload of Ashkenazim, and perhaps the odd Balkan or North African Sephardi. So far, I’ve managed to find matches in all but a few Latin American countries, plus several regions of Spain and Portugal.

Some segments of likely Sephardic origin.
The red-and-green one on Chromosome 5 is the subject of today’s post.

Not all of these matches have a story to tell—for what it’s worth, we now know that Jewish ancestry is common across Latin America, and Sephardic segments are anything but rare among Ashkenazi Jews (though my 30 breaks Brook’s previous record).

Here I’d like to focus on one genetic connection, on the paternal strand of my 5th chromosome, which proves to be an exception. A simple e-mail to I.C. revealed the story of a family with deep roots in the secret Jewish community of Trás-os-Montes in far northeastern Portugal, their tenacious preservation of a forbidden heritage, and their far-flung genetic ties to the Americas, Eastern Europe, and the East Mediterranean.

I.C., it turns out, is something of a lay expert about the Jewish community of Trás-os-Montes (“Behind the Mountains”, centered around the county town of Bragança), from which her mother’s mother’s mother hailed. When A.A., a Jewess from Duas Igrejas (a village on the border with Old León), married outside the secretive community, it caused a stir—and on the eve of World War II, she and her husband raised their daughter, N.C., non-Jewish.

Relevant locations, Trás-os-Montes.

A.A.’s family, whose pedigree extends back to the early 17th century on multiple sides, hailed from a collection of villages along the Douro with a documented history of Jewish settlement and inquisitorial persecution, chief among them Lagoaça and Vilarinho dos Galegos.

The earliest of her documented ancestors: F.G. and A.R. of Quintela de Lampaças, likely born around 1600. On October 2, 1634, the Jews of their village decided to hold Yom Kippur services—after which authorities found out, issuing arrest warrants for 19 of the participants, 9 of whom they managed to capture.

Several centuries and inquisitions later, the Jews of Trás-os-Montes forgot all but a few normative Jewish practices, developing their own code of ritual in its place. In any event, the consciousness of difference persisted down into the 20th century, where in dozens of northeastern Portugal villages, everyone knew which families were Jewish and which were “Old Christian”, as well as the limits of inter-communal comity. For example, like ought to only marry like.

But considering that starting around 1500, all secretly-professing Portuguese Jews were officially baptized alongside their gentile neighbors, can we really assume that inter-communal hanky-panky was effectively socially policed and rare?

Existing studies, limited to uniparental markers, present a mixed bag. Curiously, researchers had concluded that relative to the better-known crypto-Jewish community of Belmonte, farther south along the Spanish border, Jews from Trás-os-Montes seemed to have mixed more with the Portuguese general population. But without autosomal analysis (that is, a closer look at the 23 chromosomal pairs of recombinant DNA), it can be hard to draw conclusions about population history.

With N.C.’s genome, we have a chance to elucidate things. Now, for a reminder: N.C.’s father was born to a gentile family in Duas Igrejas in 1890; her mother was born to a Jewish family in the same village in 1916.

Using a simple population admixture Monte Carlo simulation program, we can get an answer to our basic question: what percentage of N.C.’s ancestry is Jewish, as opposed to Portuguese? (Sephardic Jews are quite genetically distinct from Portuguese and Spanish people, as Ashkenazi Jews are from German and Polish people, and so on.)

If N.C.’s father were entirely typically Portuguese, and her mother were entirely Sephardi Jewish, we would expect to get a model of 50% Portuguese and 50% Sephardi Jewish, give or take a few percentage points.

On the other hand, if her mother had picked up some gentile Portuguese admixture over the course of 13-15 generations since the original edict of forced conversion (1497) and the establishment of the Portuguese Inquisition (1536), we would expect a Sephardi Jewish share substantially lower than 50%. There is also the chance that her father might have had some Jewish ancestry, which suggests a Sephardi Jewish “maximum” above 50%.

Knowing nothing about the details of population dynamics among the secret Jews of Trás-os-Montes during the 16th to 19th centuries, one would probably assume that N.C. would come out to 25 or 30% Sephardic, maybe more, but maybe less.

As it turns out, one would be wrong. Using two-way mixes of potentially representative population averages, we yielded the following best fit in Eurogenes K13:

And its rough equivalent in MDLP K23b:

(A note: Algerian Jews are heavily Sephardic, and Galicians (from northwestern Spain) speak a dialect of Portuguese. Working with Eurogenes K13 population averages, nMonte mildly prefers Algerian Jews to Balkan Sephardim as a proxy for “Sephardic”, and prefers Galicians to the given Portuguese sample as a proxy for “northeastern Portuguese”. MDLP K23b prefers the 2 obvious populations.)

The crux:

Two models using the best amateur “admixture calculators” out there estimate that N.C. is between 47% and 58% Sephardic, and between 42% and 53% Portuguese. This corresponds strikingly to the null hypothesis of a “fully Jewish mother, plus a gentile father”—and might as well be taken as direct confirmation of a 50-50 blend.

N.C.’s mother, A.A., was likely of ~100% Jewish origin. While other Jews from Trás-os-Montes might test differently, this result is of broader relevance than just one individual’s Jewish limpieza de sangre. Because A.A.’s family originates in a wide range of locations across Trás-os-Montes, this result suggests the existence of crypto-Jewish kinship networks across northeastern Portugal that maintained very strict endogamy for ~400 years. This possibility can be further illuminated by testing more individuals of recent crypto-Jewish ancestry (it’s unlikely that there are many of full Jewish stock left, but half- and quarter-Jewish individuals, like N.C., will do).

And when you accept this finding, things begin to fall into place. Secret Jews, known pejoratively and with a wink as Cristãos Novos (New Christians), were viewed by their neighbors as necessary partners in trade, but were otherwise considered a race apart, too disreputable to marry—while they themselves took to shunning members of the clandestine tribe who got too chummy with members of the outgroup.

A caveat:

Both of these two models exceeds the ideal 2-3% distance limit, meaning that while the proportions of our models make an impressive case for Jewish endogamy in Trás-os-Montes, the degree of fit could be a bit better.

For starters, I would guess that none of the Sephardic reference populations are pure representations of the medieval Spanish/Portuguese Jewish population. Turkish, Greek, and Bulgarian Sephardim are likely to have mixed with Ashkenazi and Romaniote Jews, and all North African Jewish populations are a mix of Sephardic migrants and veteran Jewish communities.

Plus, it is possible that Trás-os-Montes Portuguese are genetically distinct from other Portuguese groups (Portuguese regional variety is not well-characterized, and Trás-os-Montes is the most isolated corner of the country), or that modern Portuguese have some Jewish ancestry, on average, making them a poor stand-in for the Portuguese gentiles of a few centuries ago.


The segment I share with I.C. and her grandmother, N.C., is also shared with several Ashkenazim, Mexicans, and New Mexico Hispanos, as well as a Chilean, a Brazilian, and an Alexandrian Sephardi Jew. It is very likely that the most recent common ancestor was a Spanish Jew, and that at least some share of N.C.’s Jewish ancestry derives from the wave of Spanish Jews who fled to Portugal around the turn of the 15th century. However, the segment of DNA we share is quite long to be 500 years old, so the possibility of a later flight from Portugal to Eastern Europe can’t be ruled out.