Could climate change be responsible for a reduction in the size of the human brain? Recent research conducted by cognitive scientist Jeff Morgan Stibel from the Natural History Museum in California has unveiled a surprising connection between climate change and a decline in brain size.
Stibel’s study, as reported by Science Alert, involved analyzing climate records and human remains spanning a 50,000-year period. Through this research, he aimed to gain insights into how humans develop and adapt in response to environmental stress. The findings, published in a scientific paper, highlight the importance of understanding the impact of climate change on brain size and, consequently, human behavior.
To carry out the investigation, Stibel examined 298 specimens from the past 50,000 years alongside natural climate records of global temperature, humidity, and rainfall.
The results revealed a notable reduction in average brain size during warmer climate periods compared to cooler ones. This study builds upon Stibel’s previous research on brain shrinkage, motivating him to delve into the underlying causes of this phenomenon.
In an interview with PsyPost’s Mane Kara-Yakoubian, Stibel stressed the critical need to comprehend changes in the human brain over time. He expressed disappointment regarding the lack of research in this area, stating, “We know the brain has grown across species over the past few million years, but we know very little about other macro-evolutionary trends.”
To gather data, Stibel collected information on skull sizes from ten published sources, resulting in 373 measurements taken from 298 human bones spanning 50,000 years. He adjusted for geographical region and gender by considering estimations of body size to accurately estimate brain sizes.
To account for potential dating errors, Stibel categorized the fossils into groups based on their age and conducted his analysis using four different fossil age spans. Additionally, he compared brain size to four climate records, including precise temperature data from the European Project for Ice Coring in Antarctica (EPICA) Dome C, which spans over 800,000 years.
Over the past 50,000 years, the Earth has undergone various climate fluctuations, including the Last Glacial Maximum, characterized by consistently colder temperatures, and the subsequent Holocene period, which witnessed rising average temperatures up to the present day.
Stibel’s analysis revealed a consistent pattern of changing brain size in Homo, correlated with climate fluctuations as temperatures rose and fell. Notably, during the Holocene warming period, which occurred approximately 17,000 years after the last glacial maximum, humans experienced a significant decline in average brain size, amounting to just over 10.7%.
According to Stibel, brain size changes tend to occur thousands of years after climate changes, indicating that species-level adaptation often requires multiple generations. This evolutionary pattern emerged within a relatively brief period of 5,000 to 17,000 years, raising concerns about the potential adverse effects of ongoing global warming on human cognition.
Stibel argues that even a slight reduction in brain size among contemporary humans could have significant physiological implications that are not yet fully understood.
Furthermore, the analysis revealed that humidity and rainfall levels also influenced brain growth, although to a lesser extent compared to temperature. Dry spells showed a weak correlation with slightly larger brain volumes.
While the study establishes a clear relationship between climate change and differences in brain size, it acknowledges that climate alone does not account for all observed variations. Stibel suggests that other factors such as ecosystem elements, indirect climate effects (e.g., vegetation and net primary production), or non-climate factors like culture and technology may also contribute to changes in brain size.
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