Dating sub-Saharan admixture in North Africa

From a paper published today in BMC Evolutionary Biology, "The trans-Saharan slave trade - clues from interpolation analyses and high-resolution characterization of mitochondrial DNA lineages":
The interpolation analyses and complete sequencing of present mtDNA sub-Saharan lineages observed in North Africa support the genetic impact of recent trans-Saharan migrations, namely the slave trade initiated by the Arab conquest of North Africa in the seventh century. Sub-Saharan people did not leave traces in the North African maternal gene pool for the time of its settlement, some 40,000 years ago.

4 comments:

Anonymous said...

I don’t understand the last sentence. Is it saying there was no admixture from ~40,000 years ago until the Arabs introduced the trading of slaves from Sub-Saharan Africa?

—Harold

n/a said...

Harold,

That's what they're saying.

The genetic information testifies that recent migrations were the main events leading to the
mtDNA pool observed nowadays in Maghreb populations. The ancestral Near Eastern pool,
remnant of the ancient Back-to-Africa migration through the Levant around 40,000 years ago
[9] is very restricted. Values for these haplogroups are around 8.6% in El Jadida and 10% in
Tunisia [6]. A bulk of the West Eurasian lineages present in Maghreb populations is
constituted by the typical Iberian sub-haplogroups H and V (12.3% and 9.9%, respectively, in
El Jadida). It is highly probable that these lineages did expand towards North Africa when
they expanded to the rest of the European continent, from Iberia, around 14,000 years ago, as
they are present in all North African populations, even in those not known as directly
historically related with Iberia [6].

Recent mtDNA data have shown that considerable local population expansions occurred in
Sahel nomadic populations around 4,000 years ago, following important movements of
northern and eastern African people towards the recently formed Sahel region. These local
expansions were revealed in one branch of the typical East African haplogroups L3f, the L3f3
almost restricted to the Chadic-speaking nomadic groups [1] and in one branch of the typical
Iberian haplogroup V in southern Tuareg populations [8]. Thus, the emergence of the modern
Sahara, beginning some 4,000 years ago, hardened existing geographical divisions and
separated peoples, forcing the black Saharans into the oases or southwards into the more
attractive lands of the Sahel.
This barrier in gene flow is evident when attending to the global L haplogroup frequencies in
African populations. There is a clear horizontal gradient across the continent, attaining values
of 95% and higher in the Sahel region in West and Central Africa, but not in the Eastern
African coast where those values are only reached around the border between Tanzania and
Mozambique. The lower values for L frequencies in the eastern African coast are due to the
southern migration of the Eurasian haplogroup M1, which is typical of East Africa. North
Africa reaches L frequencies of 20-40%, while the Arabian Peninsula and the Near East have
around 20-30% (only higher in Yemen).

n/a said...

[continued]

The coalescence ages for the L sequences observed nowadays in North Africa shows the
young ancestry of these lineages, which were originated in sub-Saharan Africa in the
Holocene. This proves that sub-Saharan people did not leave traces in the maternal gene pool
for the time of settlement of North Africa, some 40,000 years ago. And for sure, the
continuous publishing of complete L sequences across Africa will reveal still younger ancestors between L sequences observed in both sides of the Saharan desert, bringing its
introduction into North Africa to more recent/historical times.

It is also relevant that the interpolation analyses of haplogroups inside the L pool across the
Sahara revealed horizontal gradients, matching in a high extent the known trans-Saharan
routes. The West is dominated by L1b, L2b, L2c, L2d, L3b and L3d. The Center has L3e and
some L3f and L3w. The East bears L0a, L3h, L3i, L3x and, in common with the Center, L3f
and L3w. L2a is almost everywhere, strengthening its dominance in the slave package, not
only towards the New World, but also in the trans-Saharan trade.

Both these genetic evidences agree with historical data that the introduction of the Asiatic
horse into North Africa around 2,000 years ago lengthened the reach of desert nomads’
raiding and trading. Before this period, the few black slaves taken from time to time across
the Sahara would have been seen on the far side of the Mediterranean as mere exotic
household ornaments. But, it may be argued that there was no regular trans-Saharan trade
system before the rise of the camel-mounted Berber nomad, in the first Christian centuries,
and perhaps not even until after the arrival of the first camel-riding Muslim Arabs in North
Africa, in the seventh century [39].

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