A new study sheds light into a correlation between past climate changes and a reduction in the size of the human brain.
In the new study, cognitive scientist Jeff Morgan Stibel analyzed climate records and human remains spanning a 50,000-year period to explore how humans have developed and adapted in response to environmental stress.
The study specifically examined brain size changes in 298 Homo specimens over the past 50,000 years in relation to natural records of global temperature, humidity, and rainfall. The findings indicate that during periods of warmer climate, the average brain size decreased significantly compared to cooler periods.
Stibel was motivated by his prior studies on brain shrinkage and aimed to uncover the underlying causes. The study aimed to shed light on the impact of climate change on brain size and, ultimately, human behaviour.
To gather data, Stibel compiled skull size measurements from ten separate published sources, encompassing a total of 373 measurements from 298 human bones spanning the 50,000-year period. The brain sizes were estimated by adjusting body size estimations for geographical region and gender.
The fossils were categorized based on the timeframe in which they existed, and Stibel conducted his analysis using four different fossil age spans (100 years, 5,000 years, 10,000 years, and 15,000 years) to account for potential dating errors. Brain size was then compared to four climate records, including temperature data from the European Project for Ice Coring in Antarctica (EPICA) Dome C, which provides accurate temperature measurements dating back over 800,000 years.
Over the past 50,000 years, the Earth experienced the Last Glacial Maximum, characterized by consistently colder temperatures until the end of the Late Pleistocene. Holocene period followed this, during which average temperatures rose, leading up to the present day.
The analysis showed a general pattern of changing brain size in Homo, which correlates with climate change as temperatures rise and fall. Humans had a considerable decline in average brain size, amounting to just over 10.7 percent, throughout the Holocene warming period. According to Stibel, ecosystem factors like predation, indirect climate effects like vegetation and net primary production, or non-climate factors like culture and technology could all be contributing to changes in brain size.
“The results suggest that climate change is predictive of Homo brain size, and certain evolutionary changes to the brain may be a response to environmental stress,” Stibel said.
The study’s findings contribute to our understanding of how environmental factors, such as climate change, can potentially influence human brain development and evolution. The study says further research needed to deepen the knowledge of this complex relationship and its implications for human behaviour.