How the transition to agriculture affects populations in the present day


Date:
March 9, 2022
Source:
University of California - Davis
Summary:
The transition of human societies from hunter-gatherers to farmers
and pastoralists is a more nuanced process than generally thought,
according to a new study of peoples living in the highlands of
southwest Ethiopia.



FULL STORY ==========================================================================
The transition of human societies from hunter-gatherers to farmers
and pastoralists is a more nuanced process than generally thought,
according to a new study of peoples living in the highlands of southwest Ethiopia. The work was published March 9 in Current Biology.


==========================================================================
Much of the study of how people transitioned away from a lifestyle based
mostly on food collected from the wild to one based on cultivated crops
has focused on Europe, where the shift to agriculture, or "Neolithic transition," concluded thousands of years ago. Based largely on genetic studies, the prevailing view is that the transition occurred mainly by population replacement rather than cultural change, said first author Shyamalika Gopalan, a graduate student at the time of the work advised
by Brenna Henn, associate professor of anthropology at the University
of California, Davis.

"The prevailing view has been that in Europe it was a wave of people
that came through and replaced everyone," Gopalan said.

The transition to agriculture is still underway in the highlands of
southwest Ethiopia. Farmers and pastoralists started moving into the area
1,500 to 2,000 years ago, encroaching on the resident hunter-gatherers,
and the groups have since been living alongside each other. That presents
an opportunity to study this transition and the degree to which it
represents replacement versus cultural change in the present day and a different global context.

The team, led by Henn and Barry Hewlett at Washington State University, Vancouver, collected DNA samples from five groups of people in the
southwest highlands: the hunter-gatherer Chabu; the Majang, who practice small-scale cultivation of crops; and the Shekkacho, Bench and Sheko,
who practice more intensive farming. The goals were to assess both the
genetic ancestry of the different groups and demographic trends in the
recent past.

"Based on genetics we can estimate the effective population size over
the past 60 generations, or about 2,000 years," Gopalan said.



==========================================================================
Last hunter-gatherers The Chabu are the last hunter-gatherers in the
area. They were considered a subgroup of the Majang, but the research
team found they have a distinct genetic profile, said Justin Myrick,
field manager for the Henn laboratory and a staff researcher at the UC
Davis Genome Center.

The new analysis shows that the Chabu are related to a hunter-gatherer
ancestor who lived in the area about 4,500 years ago. Contrary to
expectations based on the European Neolithic transition, the other
agricultural groups in the study also have a majority genetic affinity
with these hunter-gatherer ancestors, though they differ in their other ancestries. The Majang have genetic input from Nilo-Saharan speaking agriculturalists. The Bench and Sheko, in contrast, have contributions
from East African Afro-Asiatic agricultural ancestors - - from whom the Shekkacho are mainly descended.

The population size estimates show that the Chabu have been declining
over the past 2,000 years. That is often, but not always, the case for hunter-gatherer groups during an agricultural transition, Gopalan said, although at least from what we can see in Africa, demographic responses
are heterogenous.

Hunter-gatherers may find new roles living alongside agriculturalists
as specialists, providing services such as blacksmithing.

"What's really interesting here is that we have groups in this study from
the same area who have transitioned to agriculture at different times,
with the Chabu in transition right now," Myrick said. "What we see is
a lot of variation in response to agriculture. The Chabu and Majang's population sizes have been declining, though the Bench and Sheko have not despite all of them having majority indigenous hunter-gatherer ancestry."
"The European Neolithic agriculturalist replacement model isn't bearing
out in East Africa -- there's more admixture going on and culture change," Myrick said. "The process is very complicated, and there may be many
factors contributing." Gopalan is now a postdoctoral scholar at Duke University. Additional authors of the paper are: at UC Davis, Austin
Reynolds and Mira Mastoras; Richard Berl and Zachary Garfield, Washington
State University; Barnabas Bafens, Bench Sheko Zone Administration,
Mizan, Ethiopia; Gillian Belbin, Icahn School of Medicine at Mount Sinai,
New York; Cole Williams and Michelle Daya, University of Colorado,
Anschutz Medical Campus; Akmel Negash, Hawassa University, Ethiopia;
and Marcus Feldman, Stanford University. The work was partly supported
by grants from the National Institutes of Health.


========================================================================== Story Source: Materials provided by
University_of_California_-_Davis. Original written by Andy Fell. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Shyamalika Gopalan, Richard E.W. Berl, Justin W. Myrick, Zachary H.

Garfield, Austin W. Reynolds, Barnabas K. Bafens, Gillian Belbin,
Mira Mastoras, Cole Williams, Michelle Daya, Akmel N. Negash,
Marcus W.

Feldman, Barry S. Hewlett, Brenna M. Henn. Hunter-gatherer
genomes reveal diverse demographic trajectories during the
rise of farming in Eastern Africa. Current Biology, 2022; DOI:
10.1016/j.cub.2022.02.050 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220309111117.htm

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