Using a large assemblage of human fossils from Ice Age Europe, paleoanthropologists have identified a population turnover in Western Europe at 28,000 years ago, isolates in western and eastern refugia between 28,000 and 14,700 years ago, and bottlenecks during the latest Ice Age.
An artistic reconstruction of a hunter-gatherer group from the Ice Age. Image credit: Tom Björklund.
“Around 45,000 years ago, the first modern humans migrated to Europe during the Ice Age, marking the beginning of the so-called Upper Paleolithic epoch,” said Dr. Hannes Rathmann, a researcher at the University of Tübingen.
“These early groups continuously populated the European continent, even during the so-called Last Glacial Maximum about 25,000 years ago, when glaciers covered large parts of northern and central Europe.”
“Archaeologists have long debated the influence of climatic changes and the associated new environmental conditions on the demography of hunter-gatherers at that time.”
“Due to the limited number of fossils available and their often poor molecular preservation for ancient DNA analysis, it has been very difficult to draw conclusions about the impact of climatic factors on migration, population growth, decline, and extinction.”
As teeth dominate the fossil record and preserve genetic signatures in their morphology, Dr. Rathmann and colleagues compiled a large dataset of 450 dentitions dating between 47,000 and 7,000 years ago.
They focused on morphological tooth traits — small variations within the dentition, such as the number and shape of crown cusps, ridge and groove patterns on the chewing surface, or the presence or absence of wisdom teeth.
“These traits are heritable, which means we can use them to trace genetic relationships among Ice Age humans without requiring well-preserved ancient DNA,” Dr. Rathmann said.
“As these features can be observed with the naked eye, we also examined hundreds of published photographs of fossils.”
The results show that from around 47,000 to 28,000 years ago — during the Middle Pleniglacial — populations in Western and Eastern Europe were genetically well connected.
In the subsequent period, the Late Pleniglacial, between 28,000 and 14,700 years ago, the researchers found no genetic connections between Western and Eastern Europe.
In addition, the analyses show that both regions experienced a significant reduction in population size, which led to a loss of genetic diversity.
“This drastic demographic change was probably caused by massive climate changes,” Dr. Rathmann said.
“Temperatures during this period dropped to the lowest values of the entire Upper Paleolithic and culminated in the Last Glacial Maximum, a time when ice sheets reached their greatest extent and covered most of northern and central Europe.”
“The deteriorating climate caused a shift in vegetation from steppe to a predominantly tundra landscape, which affected the habitats of prey animals and, consequently, the hunter-gatherers who depended on them.”
“Our results support the long-held theory that populations were not only driven southward by advancing ice sheets but also separated into largely isolated refugia with more favorable environmental conditions,” said Dr. Judith Beier, also from the University of Tübingen.
Another remarkable finding of the study is the discovery that populations in Western Europe went extinct at the transition from the Middle to the Late Pleniglacial and were replaced by a new population that migrated from Eastern Europe.
After the Late Pleniglacial, temperatures steadily rose again, glaciers retreated, and steppe and forest vegetation returned, allowing for the first recolonization of previously abandoned areas.
The team observed that during this period, the previously isolated and greatly reduced populations in Western and Eastern Europe began to grow again in numbers and migration between the regions resumed.
“Our new method has enabled us for the first time to reconstruct complex prehistoric demographic events using morphological data,” said Dr. Maria Teresa Vizzari, a researcher at the University of Ferrara.
“As far as we know, this has never been achieved before.”
“Our study provides important insights into the demographic history of Ice Age Europeans and highlights the profound impact of climate and environmental changes on the lives of prehistoric humans,” Dr. Rathmann said.
“We should urgently learn from our past if we want to address the complex environmental problems of the future.”
The findings were published in the journal Science Advances.
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Hannes Rathmann et al. 2024. Human population dynamics in Upper Paleolithic Europe inferred from fossil dental phenotypes. Science Advances 10 (33); doi: 10.1126/sciadv.adn8129
This article was adapted from an original release by the University of Tübingen.
