Northern Cameroon is home to two major Y-DNA genetic outliers. A group Chadic language speaking people, a majority of whose men are genetically related most closely to the Atlantic modal haplotype, in a variant found nowhere else, and a group of Niger-Congo language speaking Fulani people where one of six of their men have a type T haplotype (discussed previously at this blog two post ago), which is found in the Nile River Valley, Somolia, Southern India, Mesopotamia and at low frequency in Central, Eastern and Southern Europe.
My prior post described my hypothesis that the type T haplotype came to India from Africa, rather than the other way around. But, how did T and R1b end up in Northern Cameroon in the first place where they are outliers?
Here is a plausible story.
Northern Cameroon is where you get dumped if you follow the White Nile to its source and then hop over a very low mountain range to the next river system over which is one or two more days journey on foot.
My hypothesis is that both T and R1b expand up the Nile Valley from the Near East/Balkans, follow it up the White Nile get dumped in North Cameroon. They can't go any further since Niger-Congo speaking Y-DNA type E haplotypes with farming suited to the region (Sahel farming slightly predates Near Eastern farming) are already established and in the way.
The T types present throughout the Nile Valley probably bring Mesopotamian package farming to Egypt (which is the direction it happened) and subsequently get diluted especially on the Egyptian end by new migrants to Egypt, which is one of the two major civilization centers of the ancient world. In this view, the T types are the early Neolithic population (ca. 7000 BCE - 6500 BCE), which explains their presence in early Neolithic areas of Europe via the Balkans as well. The T haplotype men, unable to farm with their package of crops from the Near East, they have to rely solely on the herd animals once they reach Cameroon.
Sister haplogroup K to type T (which was called K2 until less than a decade ago), in contrast, is strongly associated with the Harappan population descended from Sumeria, and to a lesser extent with Caucusian immigration from Mesopotamia, so an early Mesopotamian orign makes sense. But, the T area and K area do not strongly overlap (hence supporting the Afro-Dravidian hypothesis, and I am still not willing to speculate regarding whether that migration is by land via the Nile, or by sea along the Atlantic Coast via Minoan sailors, or to the East African coast and then by sea to India).
R1b, I hypothesize, comes to the region later than T, but before the Old Egyptian dynasty which could exclude them (perhaps 5500-6500 BCE rather than 15000 BCE as sometimes suggested), but they are herders in the first place. They move rapidly through the Nile Valley much more rapidly as a result, and thus don't leave a genetic trace there. However, they keep their own Afro-Asiatic language that diverges into Chadic, unlike the older T haplotype group that adopts the Niger-Congo languages and admixes to a much greater extent and adopts Sahel farming to some extent, because they've been there longer. (Now, notably, the two groups which are now both Islamic herders are starting to admix with each other and lose separate ethnic identities).
The Case for a Hyskos Dynasty Era Migration
It is tempting to put the R1b migration even later in the Hyskos dynasty in Egypt (ca. 1900 BCE), but one would expect some Semitic J Y-DNA haplotypes in the group if this were the case, because the foreign Hyskos dynasty in Egypt was believed to be Semitic in origns, and there is already a known back migration to Africa of Ethiopic Semitic languages (which appear to all descend from a single proto-language) around then that is a much better fit.
Ethiopia, of course, is where you get dumped if you trace the Nile Valley to its Blue Nile source. The proto-Ethiosemites could have traced the Blue Nile, while the proto-Chadic people could have traced the White Nile, perhaps both at the suggestion of the expansionist Hyskos dynasty in small numbers that expanded when they arrived.
If R1b does date to the Hyskos (by permission from them probably) it would have to have been quite a small group to escape offical mention in the area where there are the best records, particularly in light of the fact that this was a complete group of men and women, suggesting that the group couldn't have been that small. The strongest argument in favor of a Hyskos rather than a pre-Old Dynasty origin for the Northern Cameroon Chadic peoples is that they aren't very admixed for a population that has been in the area only a little longer than the very admixed T haplotype Fulani in Northern Cameroon.
A Dead Sea Clue?
Notably, one of the other ancient R lineages (R* basically) like the Cameroon subtype which is quite different from the R types most commonly found in Europe and South Asia, was found at high frequency (about 40%) among men in the Dead Sea area. This would suggest that R split up into subtypes further South than it is mostly observed now (perhaps in and around Jerico in or just prior to the early Neolithic) and this would be a plausible geographic source for the Cameroon branch of R1b that fits the time window that I suggest.
A Mixed Gender Migration
The matralineal lineages Chadic people of North Cameroon (who are associated with the outlier R1b Y-DNA haplotype), as well as the men, are genetically distinct from the rest of sub-Saharan Africa
Dating African Livestock
Some archeological studies argue for a quite recent introduction of goats and sheep to sub-Saharan Africa around 2200 BCE, while others make a case for a much earlier date around 7500 BCE in the Nile River Valley and perhaps not much later immediately beyond it. The recent date would fit with the North Cameroon Chadic and Ethiosemitic peoples both bringing goats and sheep around the time of the Hyskos dynasty.
The earlier date would suggest that goats and sheep might have arrived with the T haplotype population of the Northern Cameroon Fulani, with the other groups constituting later waves of herders at an undetermined date.
Footnote on the History of R1b and R1a
As a footnote, many people associate Y-DNA type R1a with the proto-Indo-Europeans. The association shows up in India (it is most common in high caste Indo-European language speakers), but I doubt that R1a is specific to Indo-Europeans in Europe. More likely, R1b and R1a constitute two different wings of the early Neolithic farmers that brough the Near Eastern agricultural package to Europe. R1a is a fit to the Linear Pottery culture and its cultural descendants that brought agriculture up from the Balkans through the river basins of Eastern Europe and expanded to towards Central Europe from there; while R1b, the Atlantic modal haplotype, is a fit to the early Neolithic population that expanded along the Mediterranean and Atlantic coasts associated with the Corded Ware culture and its successors and also with the megalithic structures seen in the Atlantic area.
In my view, as expressed in my previous previous post, the Indo-Europeans, whose defining genetic tell is the Anatolian J2 haplotype (a good argument for an Anatolian or Caucasian homeland for the Indo-Europeans rather than a Balkan or Central Asian one, by the way), came much later. R1a, in contrast in my view, is likely to be a haplotype associated was a pre-Indo-European farmers who may have either turned to herding when they reached Central Asia (herding emerges contemporaneously with the emergence of farming, unlike hunter-gatherer lifestyles which far precede both), or may have been a deeper substrate of the farming population to which which J2 people (associated with origins in Mesopotamia and Anatolia) were added later on, that merged into the proto-Indo-European peoples not long before they entered India.