To reach this conclusion, the researchers compared the evolution of Homo sapiens brain size with climate records. Perhaps, finally, an explanation.
The size of the human brain has been shrinking over the past few millennia, a phenomenon that has long intrigued anthropologists. The answer is surprising, to say the least: it could be an adaptive response to climate change, according to a team of researchers from the California Museum of Natural History, who compared the evolution of the brain size of 298 Homo sapiens specimens over the past 50,000 years with climate records (temperature, humidity, precipitation) on a global scale over the same period.
Climate protest in Paris on April 9, 2022. This research, recently published in the journal Brain, Behavior and Evolution (new window), aims to understand better how humans develop and adapt in response to environmental stress (new window), explains Jeff Morgan Stibel, a cognitive scientist and lead author of the study. “Given recent global warming trends, it is essential to understand the impact of climate change, if any, on human brain size and, ultimately, human behavior,” the scientist emphasizes, quoted by the Science Alert website (new window).
Its size has decreased by about 10.7%
By analyzing the data, the team of scientists found that the average size of the human brain has decreased significantly when the climate has warmed, compared to colder periods.
Average temperatures declined until the end of the Late Pleistocene, about 12,000 years ago. The Holocene then saw average temperatures increase, which has continued to this day. However, during this period, the average human brain size decreased significantly, by about 10.7%, or the size of a tennis ball.
The analysis showed that humidity and precipitation levels also affected brain growth, although temperature was a more important factor. “Changes in brain size appear to occur thousands of years after climate change, and this is particularly pronounced after the Last Glacial Maximum, about 17,000 years ago,” the researcher explains.
This evolutionary pattern occurred over a relatively short period, from 5,000 to 17,000 years ago. Climate does not seem to explain all the variations. According to the researcher, non-climatic factors, such as predation, but also culture, and technology, could also contribute to the decrease in brain size. “Further work will be needed to determine whether the impact of climate change on [homo sapiens] physiology is specifically the result of temperature changes or an indirect effect due to other elements,” the researcher admits. This reduction in the brain does not mean that modern humans are dumber than their ancestors. A similar parallel exists between domesticated animals and wild animals.
Dogs have smaller brains than wolves but are more intelligent and sophisticated because they understand human communication gestures.
