Of DNA and History
During the hot and violent summer of 2002, while one after another suicide bomber was tearing
himself and society apart, a group of scientists gathered in Tel Aviv to discuss our common genetic
heritage. The meeting concerned “ancient DNA,” which means DNA, the substance of genetic
inheritance, as it can be found in anything no longer living. This brought together participants from
around the world, ranging from forensics experts to anthropologists, archaeologists, and molecular
biologists. Like fossils themselves, DNA can sometimes persist for decades or millennia under the
right conditions. Over time, it degrades; its original configuration as chains billions of bases
(“letters”) long is converted to short pieces of perhaps several 10s or 100s of bases. It is as if a
newspaper is slowly ripped to shreds. The scientist’s job is to take the fragments of the newspaper
and then attempt to reassemble the news of the day from the individual phrases.
The task is not so hopeless as it sounds, however. We know very much about the human
genome, the DNA of a cell including all the genes specifying the instructions of life, and we
understand how it may change over time. Comparing the DNA from one individual – or fossil –
with that of another allows us to determine how closely related those two individuals are or were.
We can say, for example, if one is the offspring of another, or if they were likely members of the
same tribe. Given ancient samples, it may be possible to reconstruct events in human pre-history,
or events in recent times left unrecorded by our historians. Sometimes the DNA studied is not very
ancient, but nonetheless not from the living. The chief scientist in charge of identifying the victims
of the attacks on the World Trade Center was at the meeting and reported on the methods his team
devised. The researchers who identified the “unknown child” of the Titanic were also there. We
can also make inferences about the past by studying materials from the living.
A few examples suffice to illustrate the power and interest of this area of research. Several
years ago, studies of “molecular markers” – fingerprints based on differences in patterns within the
genome – showed that the Palestinians as a group are not, genetically, most similar to those from
the Arabian peninsula as might be expected if they were descendents of invaders, but rather are
most closely related to the Sephardi Jews. This indicates that a local indigenous population, of the
same ancestry as the original, per-Galut Israelites, were converted to Islam by a fairly small number
of clerics or soldiers and not that a large group of invaders settled in a land emptied by the Romans.
Among the Palestinians are Christians and Muslims, the Muslims being in the large majority. Islam
was founded and reached Palestine well before the Crusade arrived in the Holy Land, so it is easy to
think that the Palestinian Christians might have been Muslims converted, again at the sword, to
Christianity. However, the data reported at the meeting in Tel Aviv shows that the Palestinian
Christians are genetically closer to the Jews than to the Muslim Palestinians. This suggests that
they represent an ancient group of Judeo-Christians that persisted in Israel since ancient times, and
may have been already Christian when the Crusaders arrived.
Coming to a more local population, as we all know the archipelago between Sweden and
Finland is Swedish speaking. In the Middle Ages, it had the highest population density of the entire
Nordic region, due to its proximity to a steady source of food (fish) and major trade routes along the
Baltic. The islands today look more to Stockholm for their culture than they do to Helsinki, and it
one might think that, indeed, the settlers in ancient times came from the western side as well.
However, when Ålanders are tested genetically, it turns out that they are more similar to the Finns
of today than to the Swedes. One suspects that the wide channel separating the main island from
Swedish coast proved a greater barrier in ancient times than did the small bays stretching back to
the Finnish mainland, and the bulk of the settlers, but not the language, in fact arrived from the east.
Perhaps the biggest surprise of the meeting, at least for me, was that of the Levis. Although
one’s identity as a Jew is fixed by the religion of one’s mother, the ritual status of a Jewish man is
determined by that of his father. Fathers who are Cohens have sons who are Cohens, and fathers
who are Levis have sons who are Levis. Biologically, our gender is also decided by our fathers:
one pair of chromosomes does the job. Boys have one “X” chromosome and one “Y”, girls are XX.
Since mothers are also therefore XX and fathers XY, the mother can give only an X chromosome to
the offspring, but fathers either an X or a Y, thereby determining the sex of the offspring.
Conveniently, then, both ritual status and gender rides on the Y chromosome: all boys who are
Cohens should therefore have a “Cohen” Y chromosome, and all boys that are Levis should have a
“Levi” Y chromosome. One can distinguish between the Y chromosomes of different groups by
“polymorphisms,” meaning differences in the pattern of molecular markers found on the DNA of
the chromosome. This clever observation was shown, in 1999, to be true for the Kohanim: the
present-day Cohens share a particular polymorphism found on the Y-chromosome; it is
considerably more frequent among this group than among other Jews, or among non-Jews. Details
of its change over time are consistent with an origin of the Kohanim as a distinct group in biblical
times. This was a deeply satisfying finding, confirming our ideas of Jewish peoplehood.
The same British research group that reported these findings went on to study the Levis.
Here, however, the results were surprising. The Levis split into two groups based on their Y
chromosomes, along the Sephardi – Ashkenazi divide. The molecular fingerprint of the Y
chromosomes of the Sephardi Levites fit into the Middle-Eastern framework well – it is highly
likely that the Sephardi Leviim are a homogeneous group descended of the Leviim of biblical times.
The Ashkanazi Levites likewise hold together as a single group. However, their Y chromome is not
of Middle Eastern origin – the ancestor of all current Askenazi Levites was a Sorb, a member of the
western-most Slavic tribe. The Sorbs came into contact with the Jews in late Roman times, when
Jewish settlements were founded in the Rhineland, and before the communities were organized.
The data indicate, then, that a woman married to a Levi bore a child by a Sorb man, but the male
offspring retained the religious status of his non-biological father. The social circumstances
surrounding this event are of course lost to time. One might wonder what happened to all the other
Ashkanazi Levites. The answer is that, through random processes, this one paternal line came to
replace all others, so far as the Y chromosome is concerned. The is not to say all Ashkanazi Levis
are half Sorb; because chromosomes assort independently, only the Y chromosome but not
necessarily others have persisted from the Sorb ancestor. As we all know, some men have many
grandchildren, and others none. Over time, some family lines die out, and others become very
widespread. This appears to have been the case among the Ashkanazi Levites.
For virtually all nations, their sense of identity is a mixture of cultural, political, and genetic
factors. People in Finland will say someone looks “unfinnish,” meaning that they do not share
variants of the few genes determining facial structure and hair color with the majority of Finnish
citizens. Nations also have myths about themselves – “we came from the Urals,” or “out of Egypt,”
which help solidify national identity. Modern genetic methods now enable evidence to be gathered
which support or do not support these claims, allowing us to propose explanations for events in prehistory. This is not the same as proving a certain tradition false, and the use of genetics to make
political claims is also suspect. An adopted child has no genetic claim to his new family, yet the
child inherits full social membership in that family.
The inhabitants of Åland may be amused by new data on their ancestry, but it is doubtful
that widespread knowledge of this will affect their autonomous status. The Christian Palestinians
would find their relative closeness to the Jews inconvenient, certainly not something likely to make
life among their Muslim neighbors easier. As for the Ashkanazi Leviim, there is a theoretical
problem. One cannot inherit Levitical status by adoption. If (when) the Temple is rebuilt, the data
would indicate that only Sephardi Leviim are suited for roles in the Temple. Of course, it will be
rabbis and not geneticists that will decide this, and I strongly suspect that the response from the
Rabbinate, if they were aware of the situation, would either be deafening silence, or a stony “who
asked you?” Perhaps it is just as well, for the sake of the unity of the Jewish people, such that it is.
As a small aside, genetic studies also indicate that among the general Western population, up to 10
% of children are not offspring of their socially defined fathers. For the September 11th victims,
when the data indicated this to be the case, the families were not informed. Again, the information
in most cases would not be welcome.
In the final analysis, it is important to remember that genetic fingerprints are like those on
our fingers – not very important except as identity tags. Sequencing of the human genome and
molecular marker studies have confirmed what we ought to realize anyway: that mankind is one
family, very closely related to each other, with genetic differences between individuals on the order
of a few tenths of one percent. If the Sephardi Jews are closest genetically to the Palestinians, the
Ashkenazi Jews are closest to the Syrians. It is this very closeness of all human beings, though, that
makes the political gulfs between us all the more tragic.
© Alan H. Schulman 2003. All rights reserved.