Q&A for History of Mankind (18)
Climate change in the Indus Civilization collapse & the origins of North African farming
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This is the eighteenth Q&A for History of Mankind. Paying subscribers received an email soliciting questions and I got some.
I picked three that I think I can help the most with, and they’re all below the paywall. But today first let me present not one, not two, but three recent papers that I think shed a lot of light on pre-historic events.
The first one looks back at a little-known, but extremely important moment in Earth's climate history. The global climate became significantly cooler and drier after 3000 BC and particularly after 2200 BC. A so-called 4.2 Kiloyear Event has been postulated to explain the trend, even though evidence from the Sarasvati basin, China and elsewhere signals that the cooling had started well before something happened in the North Atlantic that may have led to colder weather.
In any case, in climate history this Event kicked off the current Meghalayan Age, the one in which we live, in which the climate – despite an uptick since the 19th century – remains, generally speaking, colder than during the preceding millennia up to the ultra-cold and ultra-dry Younger Dryas period, ended in 9600 BC, discussed here:
A 2022 paper postulated that a quick decline in Maltese architectural complexity marking the end of the so-called Temple Period may be related to the cooling phase, as it resulted in lower agricultural output. These findings have now been further reinforced by the paper “Recurring summer and winter droughts from 4.2-3.97 thousand years ago in north India,” by Alena Giesch et al (Nature, 4.4.2023) -- showing that repeated intensely dry period started around that time spanned multiple generations.
The massive deficits in winter and summer rainfall affecting the Indus Civilization that Giesch and her colleagues found are extremely important for human history and, in particular, the history of India, since they almost certainly kicked off the final decline of the Indus Civilization. As I wrote before:
Even as part of the population moved to Punjab – the modern economic center of Pakistan, with a capital in Lahore; in the Indo-European Sanskrit language, Punjab means the “Five Waters” that feed the Indus – surrounded by ever-drier grasslands turning into semi-desert, a decrease in available water hit the entire region hard and migration towards the wetter lands of southern India may have been significant. This led to the spread of the Dravidian language and traditions in a wild region still in the grasp of ancient traditions such as those that left behind massive ash mounds still visible throughout .
Trade in the urbanized north fell and the last substantive contacts with Mesopotamian traders, to whom the Indus area was known as Meluhha, seem to have taken place not long after 2000 BC. Mohenjo Daro and Kalibangan were entirely abandoned around this time, as the Sarasvati River turned into the intermittent, much-reduced Ghaggar and Hakra endorheic rivers , unable to sustain a large permanent population.
Along the Indus proper, immigrants struggled to stay within large urban settlements, since that river is prone to much stronger floods and radical changes of course than the Sarasvati, or even the Ravi. Much of their experience and technology was inadequate to tame a river that has twice the flow of the Nile: during floods the river in the plains of Sindh, at the mouth of the river, can be over 16 km wide, since the gradient is very low, and there's little ground rock to keep the course stable. Various agricultural techniques were devised to make farming work along the Indus, with various degrees of success. Small artificial courses were dug into natural channels to try and put floods under control, and lifts were used to bring water onto the fields when water levels dropped .
A region that was once covered by forests and lush grasslands with tigers, elephants and rhinoceros depicted on seals lost much of its wildlife and available prey. Brick-burning, indispensable to build and repair large towns and cities with granaries, waterworks and public buildings, became much harder when wood became much scarcer.
On the Indus, life was difficult, less predictable than on the Sarasvati; earthquakes, very uncommon in Egypt and Mesopotamia but frequent in the Indus basin, added to the difficulties, amid unknown tensions that contributed to reduced agricultural surpluses, wealth accumulation and trade, and a return to earlier, small-village patterns of settlement.
A later paper, looking at the contemporary conditions in the southern Sahara (“The African Holocene Humid Period in the Tibesti mountains (central Sahara, Chad): Climate reconstruction inferred from fossil diatoms and their oxygen isotope composition” by Abdallah Nassour Yacoub et al) highlights an abrupt process of desiccation across the southern Sahara from around 3000 BC.
This paper notes that lakes as deep as 300 meters disappeared completely within a few centuries amid a cooling climate that the authors attribute to “gradually declining summer insolation.”
The third paper pertains to the even more distant past Like I wrote in the fourth installment of the History of Mankind project, the issue of just exactly how farming arrived in the North Western quadrant of Africa, the Maghreb now comprising Morocco, Western Sahara, Algeria and Tunisia, has always been a bit of a mystery.
Now, the mystery is less mysterious: it was European migrants, likely arriving from modern Spain, who brought farming, according to the paper “Northwest African Neolithic initiated by migrants from Iberia and Levant,” by Luciana G. Simões et al (Nature, 7.6.2023):
“In northwestern Africa, lifestyle transitioned from foraging to food production around 7,400 years ago but what sparked that change remains unclear. Archaeological data support conflicting views: (1) that migrant European Neolithic farmers brought the new way of life to North Africa1,2,3 or (2) that local hunter-gatherers adopted technological innovations4,5. The latter view is also supported by archaeogenetic data6. Here we fill key chronological and archaeogenetic gaps for the Maghreb, from Epipalaeolithic to Middle Neolithic, by sequencing the genomes of nine individuals (to between 45.8- and 0.2-fold genome coverage). Notably, we trace 8,000 years of population continuity and isolation from the Upper Palaeolithic, via the Epipaleolithic, to some Maghrebi Neolithic farming groups. However, remains from the earliest Neolithic contexts showed mostly European Neolithic ancestry. We suggest that farming was introduced by European migrants and was then rapidly adopted by local groups. During the Middle Neolithic a new ancestry from the Levant appears in the Maghreb, coinciding with the arrival of pastoralism in the region, and all three ancestries blend together during the Late Neolithic. Our results show ancestry shifts in the Neolithization of northwestern Africa that probably mirrored a heterogeneous economic and cultural landscape, in a more multifaceted process than observed in other regions.”
Now for the questions sent by paying subscribers:
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