- A climate that nearly annihilated our ancient forebears
In the depths of the last Ice Age, approximately 45,000 years back, mankind's first anatomically modern humans departed from Africa and the Middle East, venturing into Europe. This marked the commencement of the Mesolithic era, with tiny groups initially colonizing almost the entire European continent, even during the "Last Glacial Maximum" around 25,000 years ago, when extensive glaciers engulfed Northern and Central Europe.
The significant alterations in climate and subsequent environmental conditions presented an intriguing question: what did these changes mean for the contemporary hunter-gatherers' demographic evolution? Oh boy, obtaining concrete answers is a real challenge due to the scarcity of fossils from this era, and the DNA housed in these fossils often suffers degradation, making it tricky to analyze migration, population growth, decline, and extinction from genetic data, according to Hannes Rathmann from the Senckenberg Centre for Human Evolution and Palaeoenvironment at the University of Tübingen.
An innovative approach: Examining dental data
Given the challenge of preservation, Rathmann and his research team from Italy, the USA, and Germany opted for an imaginative tactic: instead of working with DNA, they examined the dental structures of these prehistoric Europeans. Teeth, being the sturdiest human tissue, are strikingly common in archaeological excavations.
Overall, the study analyzed dental data from 450 ancient humans across Europe, dating back to 47,000 years ago and progressing to individuals who once walked the Earth around 7,000 years ago. The team focused primarily on morphological dental features such as crown cusps' number and shape, ridge and groove patterns on the chewing surface, and the presence or absence of wisdom teeth. Sure, these features are heredity-linked, allowing us to trace genetic relationships among the Ice Age humans, says Rathmann.
Ancient Europe's kinship connections: Teeth as a window to the past
Since these characteristics can be spotted with the naked eye, the research team also scrutinized published fossil photos for dental features. "Studying historical photographs for dental characteristics was a thrilling experience as it let us include crucial fossils, which unfortunately no longer exist, like those lost or destroyed during World War II. It's like piecing together fragments of a long-forgotten story," highlighted Rathmann.
The findings reveal that populations in West and East Europe were strongly connected around 47,000 and even 28,000 years ago. This concurs with our existing archaeological knowledge, which points out widespread similarities in tools, weapons, or portable art from various regions, explained co-author Judith Beier from the University of Tübingen.
The era of big game hunters
During these times, Europe's landscape was dominated by vast open steppes, capable of supporting migratory herds of mammals as their primary food source. These suitable conditions (imagine it as a grand buffet for the hunter-gatherers) might have increased population connectivity.
In the subsequent period, which wrapped up around 14,700 years ago, the researchers found no genetic linkages between West and East Europe. Analysis also indicated that populations in both regions suffered notable declines, resulting in a loss of genetic diversity. Severe climate shifts must have driven these detrimental consequences, with temperatures plummeting to their lowest point during the entire Holocene era, simultaneously expanding ice sheets in Northern and Central Europe.
"Advancing ice caps and deteriorating climate led to shifts in vegetation from steppes to tundra," explains Rathmann. "This transformation impacted the habitats of mammal prey and consequently the hunter-gatherers who relied on them for survival." The research supports the theory that populations were driven south by advancing ice sheets and isolated into relatively isolated regions with favorable environmental conditions, added Judith Beier.
At the height of the ice age, entire populations in West Europe faced extinction. However, as temperatures rose, ice caps retreated, and once-vibrant steppes and forests returned, people were able to repopulate areas previously abandoned. The previously isolated and drastically reduced populations in West and East Europe then regrew and intermingled once again.
"Our study offers valuable insights into the demographic history of Ice Age Europeans and underscores the significant impact of climate and environmental changes on prehistoric human lives. Learning from our past is crucial to face the complex environmental challenges of the future," concludes Rathmann.
The scarcity of well-preserved fossils from the Mesolithic era makes it challenging to obtain genetic data for analyzing migration and population dynamics, as noted by Hannes Rathmann. Given this challenge, Rathmann and his team chose to examine dental structures of prehistoric Europeans due to the durability of teeth and their high prevalence in archaeological excavations.
