Digital microscope images of beads from the past. Credit: Jen Miller.
Humans are social creatures, but little is known about when, how and why different populations connected in the past. The answers to these questions are important for interpreting the biological and cultural diversity that we see in human populations today. The ancient meetings can't be addressed with the use of DNA because it can't address cultural exchanges. Scientists from the Max Planck Institute for the Science of Human History have turned to an unexpected source of information to shed light on ancient social networks. The researchers found that population connection and isolation was caused by changing rainfall patterns in southern and eastern Africa.
eggshell beads are a window into the past
OES beads are ideal for understanding ancient social relationships. Humans completely transformed the shells to produce beads, meaning that they are the oldest fully manufactured ornaments in the world. There are many opportunities for variations in style. Prehistoric accessories give researchers a way to trace cultural connections because they produced beads of different styles.
Miller says it's like following a trail of bread. The beads are clues and are waiting to be noticed.
The largest database of eggshell beads was assembled by Miller and Wang. It includes data from more than 1500 individual beads unearthed from 31 sites across southern and eastern Africa. It took more than a decade for this data to be gathered.
There is a string of beads from eastern Africa. Credit: Hans Sell
Climate change and social networks in the Stone Age.
Miller and Wang found that people in eastern and southern Africa used nearly identical OES beads between 50,000 and 33,000 years ago. The long-distance social network was once connected to people in the two regions.
The result is surprising, but the pattern is clear, says Wang, co-corresponding author of the study. This is the only time period in the 50,000 years that the bead characteristics are the same.
The oldest social network ever identified is from 50–33,000 years ago, and it coincides with a particularly wet period in eastern Africa. A major shift in global climates is believed to have triggered the disappearance of signs of the regional network. As the tropical rain belt shifted southward, eastern Africa experienced a dramatic reduction in precipitation. The increased rain in the large area connecting eastern and southern Africa may have created a geographic barrier that disrupted regional social networks.
"We can see the connection between climate change and cultural behavior through this combination of paleoenvironmental proxies, climate models, and archaeological data," says Wang.
Oldupai Gorge is an important site in studies of human evolution and is experiencing drying and more irregular rainy reasons. Credit: Yiming Wang.
A story is being woven with beads.
The results of this work document a 50,000-year-long story about human connections and climate change. The data provides new insight into variable social strategies between eastern and southern Africa. The responses show that there is more than one path to success.
"These tiny beads have the power to reveal big stories about our past," says Miller. "We encourage other researchers to build upon this database, and continue exploring evidence for cultural connection in new regions."
The 50,000-year-old social network in Africa is revealed by eggshell beads. www.nature.com/articles/s41586-021-04227-2
Nature journal information.
The 50,000-year-old social network across Africa was revealed by eggshell beads.
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