Visitors to East Africa are often surprised by huge herds of cattle with a beautiful series of horn, hump and fur patterns.
Pastoralism – a way of living around herding sheep – is a central part of the identity of many Africans.
It is also an important economic strategy that is now threatened by climate change, increasing demand for meat, urban sprawl and land conflicts.
The roots of the ministry may contain clues to solve these modern challenges.
Studies suggest that traditional ways to manage livestock – moving around and exchanging with other shepherds – have enabled herders to cope with instability and economic changes in the environment.
Visitors to East Africa are often surprised by huge herds of cattle with a beautiful series of horn, hump and fur patterns. Pastoralism – a way of living around herding sheep – is a central part of the identity of many Africans
Research also helps scientists understand how millennia of herding – and livestock manure – have formed East Africa & savannah and diversity of wildlife.
How did pastoralism begin in Africa? Currently, most archaeologists believe that wild ancestors of contemporary cattle, sheep, and goats were domesticated for the first time in the & # 39; Fertile Crescent & # 39; of the Middle East.
Archaeological research shows that the sheep began to appear in and spread from what is now about 8,000 years ago in Egypt.
Throughout 5,000 years ago, shepherds bury their dead in elaborate monumental burial sites near a lakeside in Kenya.
Two millennia later, pastoral settlements were present in much of East Africa, and in 2000 there were cattle in South Africa.
Much remains unanswered: did the animals spread mainly through exchange, just as money circulates in large quantities while people usually remain seated?
Were people long distances with their herds, crossing the continent from generation to generation?
Were there many individual migrations or few, and what happened when immigrant herders met native foragers? We decided to ask these questions using ancient DNA from archaeological skeletons from all over East Africa.
Bringing together the genetic history of shepherds
Archaeologists study the waste of old people – broken clay pots, abandoned jewels, leftover meals, even droppings – but we also study the people themselves.
Bioarchaeologists examine human bones and teeth as indicators of health, lifestyle and identity.
Now it is also possible to sequence old DNA to look at genetic ancestors. Until recently, however, Africa stood on the sidelines of the & # 39; old DNA revolution & # 39; for various reasons.
Progress in DNA sequencing has created new opportunities to study African population history.
In our new research, our team buried the genomes of 41 people buried at archaeological sites in Kenya and Tanzania, more than doubling the number of old people with genome-wide data from sub-Saharan Africa.
Large herds of cattle graze near Lake Manyara in Tanzania, where they have been an important part of the economy for 3000 years
We obtained radiocarbon dates from the bones of 35 of these people – important because direct dates on human remains hardly exist in East Africa.
Working in a team meant forging partnerships between curators, archaeologists and geneticists, despite our different work cultures and specialized vocabularies.
The people we studied were buried with a wide range of archaeological evidence that links them to foraging, pastoralism and, in one case, agriculture.
These associations are not airtight – people may have shifted between foraging and herding – but we rely on cultural traditions, artifact types and food scraps to try to understand how people got their meals.
After grouping individuals based on the lifestyles we derived from associated archaeological evidence, we compared their old genomes with those of hundreds of living people and a few dozen old people from across Africa and the neighboring Middle East.
We were looking for patterns of genetic affiliation.
Some of our old monsters didn't look like other famous groups. Despite great efforts to document the enormous genetic variation in Africa, there is still a long way to go.
There are still gaps in modern data and no old data at all for much of the continent.
Although we can identify groups that have genetic similarities with the old shepherds, this picture will no doubt become clearer as more data becomes available.
Hats expanded in stages
So far, we can see that herding has spread through a complex, multi-step process. The first step was a & # 39; ghost population & # 39; – one for which we do not yet have direct genetic evidence.
These people drew about half of their ancestors from groups that lived in the Middle East or presumably northeastern Africa (a region for which we have no relevant aDNA) or both, and about half from Sudanese groups.
While this group spread to the south – probably with cattle – they interacted and genetically integrated with collectors who already live in East Africa. This period of interaction perhaps lasted from around 4,500 – 3,500 years ago.
Red dots are archaeological sites in the authors' study. Gray dots mark selected Rift Valley sites. Prettejohn & # 39; s geological Gully survey, marked by a black star, produced the oldest DNA in Kenya
After this happened, it seems that old shepherds genetically kept to themselves.
Methods that allow us to estimate the average date of mixing – that is, the gene flow between previously isolated groups – indicate integration that was largely halted by around 3500 years ago.
This suggests that there were social barriers that caused shepherds and collectors to have children together, even if they interacted in many other ways.
Alternatively, there may have been far fewer breeders than herders, so the gene flow between these communities did not have a major demographic impact.
About 1,200 years ago, we document new arrivals from people dealing with recent Sudanese and – for the first time – West African groups, associated with early iron work and agriculture.
Pottery is the Tupperware of the past – sustainable and ubiquitous at archaeological sites. But there is not always a connection between styles and ancestral identities. We compared funerals associated with two different artifact traditions – Savanna Pastoral Neolithic (A) and Elmenteitan (B) – and found no genetic differences
After this point, a social mosaic of farmers, shepherds and collectors became typical of East Africa, and it still is.
An interesting question is how early shepherds used their herds. For example, are they drinking milk?
Although many East Africans nowadays carry a genetic mutation that helps them digest milk into adulthood, this may be a recent development.
Today we have been able to test eight people in many East African livestock farmers for the genetic variant responsible for lactase persistence. Only one man, who lived in Tanzania 2,000 years ago, wore this variant.
Perhaps dairy cattle were rare, but it is also possible that people found creative culinary solutions, such as fermented milk or yogurt, to prevent indigestion.
Cultural and biological diversity are not the same
Archaeologists have a saying that & # 39; pots are not people & # 39 ;. Certain artifact styles are not believed to reflect concrete identities – just as we would not assume today that the choice of kilts versus lederhoses is determined by DNA.
In Kenya and Tanzania, archaeologists had previously identified two early shepherd-cultural traditions, distinguished by different pottery styles, sources of stone tools, settlement patterns, and burial practices.
The people who created these cultures lived at about the same time and in the same area. Some scientists assumed that they spoke different languages and different & # 39; ethnic & # 39; identities.
Our recent study found no evidence of genetic differentiation between people associated with these different cultures; in fact we were struck by how closely related they were.
Now archaeologists can ask another question: why did different cultures arise among such closely related neighbors?
(Re) discovering lost places and people
Some of our most exciting findings came from unexpected places.
The bookshelves in the museum are full of potentially game-changing collections that have yet to be studied or published.
In a back corner of a storage room we found a tray with two fragmentary human skeletons uncovered during a geological expedition in the Rift Valley in Prettejohn's Gully in the 1960s.
There was little contextual information, but with the encouragement of curators, we sampled the remains to see if we could at least determine their age.
Archives form an important part of old DNA research, which sometimes leads to the rediscovery of long forgotten archaeological collections
We were shocked to hear that these 4,000-year-old burials were the oldest DNA in Kenya and that the man and woman buried in that place were perhaps one of the earliest shepherds in East Africa.
Thanks to them, we can demonstrate that the spread of herding in Kenya included different separate movements of ancestral different groups.
We have a lot to learn from older collections and archaeologists do not always have to dig to make new discoveries.
Old DNA research does not only answer questions about our shared past.
It also calls new ones that have to be answered by other fields. Our results do not tell us what migration and mixing mean in social terms.
What led people to move with cattle? What happened when people with radically different lifestyles met?
What has become of the collectors who have lived the entire past in East Africa, and whose descendants of these descendants are today and few?
Ultimately we hope that by studying the past in the past – and demonstrating the resilience of this way of life – we can somehow contribute to understanding the challenges that shepherds face today.
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