A recent study reveals connection between climate change and reduced brain size in modern humansafter it was published in the scientific journal Brain, Behaviour, and Evolutionwhich delved into the relationship between brain size evolution and obesity in modern humans.
Previous research has established a connection between reduced brain size and increased levels of obesity. However, this new paper explores an intriguing hypothesis suggesting that climate change could be a contributing factor to the changes observed in brain size over time.
The study proposes that the decrease in brain size among humans may be a result of natural selection driven by environmental stress, particularly in response to climate change. The researchers suggest that approximately 15,000 years ago, a period characterized by significant climatic shifts, our ancestors faced challenges that necessitated adaptive changes in brain structure.
By examining the evolutionary history of brain size, the scientists hypothesize that the environmental stressors associated with climate change may have exerted selective pressure on humans, favoring individuals with smaller brains. This reduction in brain size could have conferred certain advantages in terms of energy allocation, metabolic efficiency, and increased survival and reproductive success in challenging environments.
According to Jeff Morgan Stibel, who serves as a board member and trustee of the Natural History Museum:
As a cognitive scientist, understanding how the brain has changed over time in hominins is critical but very little work has been done on this subject. We know the brain has grown across species over the past few million years but we know very little about other macroevolutionary trends. I wrote about decreases in brain size in my last book Breakpoint, so this research was a natural extension of exploring the reasons for these changes.- Jeff Morgan Stibel, board member and trustee of the Natural History Museum
The human brain with different sparks of lines linked to it
In this study, a sample of 298 remains was utilized to examine the relationship between body size, latitude, and sex, while accounting for differences in brain size. The fossils considered in this research spanned the past 50,000 years, allowing for the analysis of two significant temperature periods: before and after the last interglacial period. To facilitate analysis, the fossils were categorized into groups representing different time intervals: 100 years, 5,000 years, 10,000 years, and 15,000 years.
To estimate brain size, cranial data from various published sources, including meta-analyses, were compiled. This resulted in a total of 373 independent cranial capacity measurements for 298 skulls. These measurements were used to estimate brain size. The obtained brain size data were then compared to four climate records.
The data used in this study were sourced from a variety of references, including the EPICA Dome C dataset, which provides surface temperature data dating back approximately 810,000 years. For more comprehensive information about the dataset, please refer to the following link.
“The most important thing to understand is that the human brain continues to evolve. Here, we found macro-evolutionary trends in brain size that happened in as few as 5-17 thousand years,” Stibel told PsyPost. “The Holocene warming period has led to more than a 10% reduction in brain size in modern humans. If global temperatures continue to warm, this could place increased evolutionary pressure on the human brain.”
Approximately 15,000 years ago, the phenomenon of shrinking brain size began, and it may have persisted up to the present day as an adaptive response. The researcher also observed that humidity and precipitation levels played a role in influencing brain size. Specifically, periods characterized by low or negligible rainfall were associated with larger brain sizes. However, it is important to note that these factors had a relatively smaller predictive impact on brain size compared to other variables.
“It is surprising how little we know about the human brain, despite it being a pretty important organ,” the researcher added.
Are there questions that ought to be addressed in the future? Stibel responded, “of particular importance to this research, there is evidence that both brain and body size are under natural selection in response to climate change. One particularly relevant question is whether one phenotype is under direct selection whereas the other is simply responding to an evolutionary correlation.”
The researcher concluded, “Even a slight reduction in brain size across extant humans could materially impact our physiology in a manner that is not fully understood.”