Thursday, May 17, 2012

Dating Cattle Husbandry In Africa

Marnie at the Linear Population Model blog has a nice post on the archaeological evidence for cattle domestication at specific points in time in specific regions of Africa (numerous citations in blog post omitted, all material below quoted from other sources):
The history of cattle in Africa is better known than that of any other domestic species; it is also very complicated because for at least three thousand years the continent has been a melting-pot for unhumped cattle (Bos taurus) brought in from Eurasia and humped cattle (Bos indicus) brought in from Asia, in particular from India. In addition, it is possible that cattle were locally domesticated in north Africa from the endemic wild aurochs (Bos primigenius).

At present, the earliest securely dated finds of cattle in a cultural context come from Capeletti in Algeria and date from the seventh to the sixth millenium BC. Other early finds have been recorded from sites in the Sahara and in west Africa. Whether these cattle originated from western Asia, through Egypt or were domesticated in Africa, cannot be determined . . . . By 6000 BP [i.e. 4000 BCE] it is probable that cattle pastoralism was well established throughout north Africa and that with the increasing desertification of the Sahara people began to move south with their cattle, only to meet the tsetse-fly belt.

The archaeological evidence for the presence of cattle in west Africa for a very long time and their continuity to the present day is provided by the small humpless N'Dama breed, which has evolved a natural immunity to trypanosomiasis, the disease carried by tsetse-fly. In east Africa pastoralism became established late in the third millenium BC, and over the next 1000 years domestic livestock slowly moved towards Tanzania. These cattle were probably humpless, for the earliest evidence for humped cattle comes from ancient Egyptian paintings dated to around 1500 BC. These authors believe that cattle with cervico-thoracic humps (i.e. with humps on their necks) were first introduced into the Horn of Africa.

If the Egyptian evidence is to be credited, the arrival of humped cattle significantly preceded the arrival of the Austronesians who settled Madagascar (which came sometime between 1000 BCE and 0 BCE) and brought Southeast Asian origin tropical plants like the banana to Africa.   Presumably humped cattle arrived in Africa from India, providing a latest possible date for trade networks that included cattle trading with India, quite possibly a maritime trade for at least part of the route (something that is known to have existed between Sumeria and the Indus River Valley ca. 1000 BCE from historical records in Sumeria and archaeological evidence; the Indus River Valley civilization emerged with a complete Fertile Crescent package of crops a thousand or two years after this package had been consolidated in the Fertile Crescent itself, around the same time that the package reached Egypt).  Another post at the same blog quoting a different source commenting on a painting from 1350 B.C.E. in Egypt sheds more light on the path that the earliest humped Zebu cattle must have taken: "The few ancient depictions of true zebu cattle always occur in the context of tribute from Syria[.]"  Hence, the last leg of the trip for humped cattle to arrive in Egypt took place either by land or sea through or along the Levant, not via the Indian Ocean, and not with the Austronesians who made their way to Africa from Borneo.

Prior African cattle having their origins either in the western Asia (i.e. the Middle East) or an independent domestication in the Nile Valley. West African N'Dama cattle appear to be derived from North African stock, whatever its provenance, and must have come at least somewhat later in time than cattle arrived in North Africa.

Give the strong association of both Chadic populations and Nilo-Saharan populations with herding, the archaeological evidence for the arrival of domesticated cattle in different parts of Africa also provides a plausible basis with which to calibrate less reliable estimates of the origins of these peoples based upon genetic mutation and recombination rates.

The quite late arrival of pastoralism in East Africa, which is also some to relict hunter-gatherer populations which are absent in North Africa and in West/Central Africa to the North of the Congo jungle, suggests that herding (and probably farming as well, at least in less arable land) may have come much sooner to North Africa and West Africa than to East Africa (with Southern Africa not experiencing agriculture until the Bantu expansion arrived there after it had swept the rest of the continent). Indeed, the arrival of  cattle herding in East Africa could conceivably have predated Bantu expansion by only a thousand years or so.

If one makes the plausible assumptions that the ancestors of Cushitic populations predate Nilo-Saharan populations in East Africa who in turn pre-date Bantu populations in East Africa, and that all of these language families were spread by cultures that employed herding or farming, the late arrival of cattle herding to East Africa (ca. 3000 BCE to 2000 BCE), the fairly well dated arrival of Bantus in East Africa (ca. 1000 BCE-500 BCE), and the known paleoclimatic wet sahara/dry sahara/chad basin size changes quite tightly constrain and compress the timing of Cushitic and Nilo-Saharan expansions in East Africa. It also probably puts the time that the source cultures for these language families arrives in East Africa sometime after the ethnogenesis of the culture that gave rise to the Niger-Congo languages that are dominant in West Africa (which necessarily predated the expansion of its Bantu branch of that language family ca. 1500 BCE-1000 BCE).

Tishkoff argues based on genetic evidence associated with the digestion of cow's milk by adults and archaeological evidence that:

Cushitic-speaking Afro-Asiatic populations . . . are thought to have migrated into Kenya and Tanzania from Ethiopia ~5,000 years ago and practice a mixture of agriculture and pastoralism . . . [while] the Nilotic-speaking Nilo-Saharan populations. . . are thought to have migrated into Kenya and Tanzania from southern Sudan within the past ~3,000 years and are strict pastoralists.
Thus, according to Tishkoff's account, Nilo-Saharan linguistic populations arrived in East Africa proper only a few centuries before the Bantu expansion reached the area, and the Cushitic population was expanding south from Ethiopia only shortly after Egypt and Sumeria developed written languages at about the same time as the high point of the Indus River Valley civilization, although their arrival in or ethnogenesis in Ethiopia clearly must have happened earlier.  Tishkoff doesn't reach a conclusion about whether a milk digestion gene specific to Africa arose first in Cushitic or Nilotic populations, but another quote from the same article strong suggests that the Cushitic people, rather than the Nolitic population was its source (and hence that the Cushitic people had cattle farming): "The absence of C-14010 in the southern Sudanese Nilo-Saharan–speaking populations suggests that this allele either originated in or was introduced to the Kenyan Nilo-Saharan populations after their migration from southern Sudan."

Tishkoff also recaps the archaeological evidence for cattle domestication in Africa:

Archeological evidence suggests that cattle domestication originated in southern Egypt as early as ~9,000 years ago but no later than ~7,700 years ago and in the Middle East ~7,000-8,000 years ago, consistent with the age estimate of ~8,000-9,000 years (95% c.i. ~2,200-19,200 years) for the T-13910 allele in Europeans. The more recent age estimate of the C-14010 allele in African populations, ~2,700-6,800 years (95% c.i. ~1,200-23,000 years), is consistent with archeological data indicating that pastoralism did not spread south of the Sahara and into northern Kenya until ~4,500 years ago and into southern Kenya and northern Tanzania ~3,300 years ago

Interestingly, the arrival of cattle herding herding in East Africa happens at roughly the same time as the South Indian Neolithic at the core of what was the approximate point of origin of the Dravidian languages which included a number of crops domesticated in the African Sahel, and only 1500 to 500 years or so before the arrival of cattle from India in Africa.  It could be that both events were the product of a single Neolithic expansion wave intermediate in time between the West African Sahel Neolithic and Bantu expansion and largely lost to recorded history since the literate caste of the two literate cultures of that time (Egypt and Sumeria) had much more narrow horizons then than they would later in their histories. We do know, however that there was significant maritime trade between Sumeria and the Indus River Valley in that era (late fourth millennium BCE) and it wouldn't be too surprising if this maritime trade network also extended to the Horn of Africa. We know that maritime trade did extend that far no later than about 0 CE which it is documented in an Egyptian geography text.

The main crops of the West African Sahel and some of the Ethiopian Highland crops are indigenous African domestications that were not part of the Fertile Crescent agricultural package. Fertile Crescent crops are a poor fit for parts of Africa beyond the Mediterranean fringe and the Nile basin; they are confined to regions further north than the regions where Fertile Crescent livestock can thrive without evolving to adapt to African weather and diseases. The quoted post dealt only with cattle husbandry, and one needs to look at dating for goats and sheep herding and for indigenous African crops to reliably date the West African and East African Neolithic (I've seen some references, that I'll have to track down, that have proposed an early date of arrival for these herd animals than for cattle.) It could be that early African agriculture didn't include cattle until other parts of the agricultural package were better established.

One possibility that could reconcile the various lines of evidence, and also relax some of the tight constraints in timing discussed above, is to envision the Cushitic languages expanding to the herding of sheep and goats, and the Nilo-Saharan expansion as being boosted by the addition of cattle husbandry to the Cushitic food production package (although, as noted above, Tishkoff's sources, at least, doubt that scenario). A comment from Marnie in the Tishkoff post on milk digestion genese also provides some dating boundaries from the original domestication of various Fertile Crescent farm animals:

Regarding the dates that Tishkoff is mentioning, she is referring specifically to cattle domestication. The earlier dates that I believe you might be referring to are for sheep and goats. Zeder's 2008 open access paper "Domestication and early agriculture in the Mediterranean Basin: Origins, diffusion and impact" has these domestication dates BP: sheep 11,000; goats 11,000; pigs 10,500; cattle 10,000(Upper Euphrates Valley). However, she states that morphologically altered domestic cattle are not found in Central Anatolia until after 8,500 BP.

I continue to think that an association of the Niger-Congo language family with the West African Sahel Neolithic is the most likely scenario, but that dating of that event as of the most recent sources I am familiar with, isn't very precise although there is some room to bound to a range of historical dates. The evidence from the arrival of cattle in the region quoted above puts that expansion at least as far back in time as the 4th millennium B.C.E. (i.e. at least more than 5000 years before present) and possibly a thousand or so years before then (i.e. as much as 8000 years before present).

Recent East African autosomal genetic data also makes clear that there was not any significant demic impact of West African Niger-Congo populations in East Africa prior to the Bantu expansion into that region, although the domesticated crops of West Africa and East Africa respectively a testaments to the mutual exchange of locally domesticated plants between the regions at some point in time.

I have seen sources that point to a very early domestication of crops in West Africa (possibly independently of contact with the Fertile Crescent Neolithic and possibly even slightly earlier than the Fertile Crescent Neolithic), such as Jared Diamond's classic "Gun, Germs and Steel", and I have also seen sources (e.g. in journal articles referenced at Mathilda's Anthropology blog, which is also references articles suggesting a two stage dissemination of herding with sheep and goats coming before cattle) that suggest that the crops that were domesticated in West Africa from indigenous plants were not cultivated in anything other than proto-agriculture (i.e. cultivation of wild plants unmodified with dietary supplementation from other sources) until around the time that the source above says that cattle husbandry arrived there. All of the sources I've seen on those points are fairly old and I don't know that literature well enough to evaluate the relative reliability of the competing sources (if I could even locate them quickly), or to know if there has been any important new discoveries in the archaeology of African farming and herding since then.

Another implication of this narrative, if it is accurate, is that within the Afro-Asiatic language family, the Berber and Coptic language families probably significantly predate the Cushitic and Chadic language families.  (These speculations don't resolve one way or the other the relative origins of Berber and Coptic languages on one hand and the Levantine Semitic languages on the other, although Ethio-Semitic languages surely broke off as a branch of the Semitic languages after all of the language families within the Afro-Asiatic macro-language family were established, probably sometime in the Bronze Age).

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