Last year, a study found that by about 3,000 years ago, the size of the human brain had decreased. This period was called the Early and Middle Bronze Age, characterized by the first empires of the Ancient Near East, which included civilizations such as Mesopotamia and ancient Egypt. The researchers believed that as humans transitioned to modern urban societies, our ancestors’ ability to store information externally in social groups diminished our need to maintain large brains.
Now, a new study led by researchers at the University of Nevada, Las Vegas (UNLV) has refuted this hypothesis.
In the previous study, the researchers explored decades-old ideas about the evolutionary reduction in the size of the modern human brain, based on a comparison with evolutionary patterns observed in ant colonies.
In a new paper published last week in Frontiers in Ecology and Evolution, the UNLV-led team looked at the data set used by the research group in last year’s study and dismissed its findings.
Anthropologist Brian Villmoare said: “We were struck by the implications of a substantial reduction in the size of the modern human brain approximately 3,000 years ago, during a time of many innovations and major historical events: the emergence of the New Kingdom of Egypt, the development of Chinese writing, the Trojan War and the emergence of the Olmec civilization, among many others.
“We re-examined DeSilva et al.’s data set and found that the size of the human brain has not changed in 30,000 years, and probably not in 300,000 years.
“In fact, based on this data set, we cannot identify any reduction in brain size in modern humans for any time period since the origins of our species.”
The UNLV researchers challenged several different hypotheses DeSilva et. Al had proposed, based on a dataset of nearly 1,000 museum specimens and early human fossils.
They noted that because the rise of agriculture and complex societies occurred at different times around the world, there should have been variation in the timing of skull changes observed in different populations.
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However, Professor DeSilva’s data set showed only 23 skulls from the time period critical to the brain shrinkage hypothesis and grouped specimens from locations such as England, China, Mali and Algeria.
The UNLV researchers noted that the data set was highly skewed, as more than half of the 987 skulls studied came from the last 100 years of the 9.8 million year period they were investigating.
Because of the unbalanced range, the team believes that previous research did not provide a clear picture of how much skull size has changed over time.
Multiple hypotheses about the causes of the reduction in modern human brain size must be reassessed if human brains have not changed in size since the advent of our species.
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