A team of researchers led by the University of Nevada, Las Vegas (USA) turns previous theories of evolution upside down, refuting a hypothesis that is becoming increasingly popular among the scientific community : the human brain does not was reduced in the 12th century BC
Thus, scientific theories that the human brain shrank as we transitioned to modern urban societies during the Holocen or have been ruled out by this work.
Dismantling theories
The researchers concluded that any assumption that a reduction in skeletal size in human evolution implied a shrinkage of the brain is unfounded.
“This is quite an exciting result because it is generally accepted that there was a reduction in brain size in modern humans,” explains Mark Grabowski, co-author of the study published in the journal Frontiers in Ecology and Evolution.
Without going any further, a recent study, from 2021, suggested that around 3,000 years ago, humans experienced a decrease in brain size stimulated by the organization of society, which meant that information storage was “clustered into the group”. This period was called the Early to Middle Bronze Age, characterized by the first empires in 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.
There was no reduction in size
“We were struck by the implications of a substantial reduction in the size of the modern human brain approximately 3,000 years ago, during an era of many important innovations and historical events: the rise of the New Kingdom of Egypt, the development of Chinese writing, the War of Troy, and the rise of the Olmec civilization, among many others”, said Biran Villmoare, also a co-author of the work. “We re-examined the DeSilva et al. and we find 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 over any period of time since the origins of our species.”
The researchers challenged several different hypotheses in work published in 2021, based on a dataset of nearly 1,000 museum specimens and early human fossils . They noted that since the rise of agriculture and complex societies occurred at different times around the world, there should be variation in the timing of skull changes seen in different populations.
According to the authors, previous research was biased. They noted that from the study’s data set, more than half of the 987 skulls studied came from the last 100 years of the 9.8-million-year time period they were investigating, so it doesn’t give a clear picture of how long it has been. The size of the human skull has changed over time.
Referencia: Brian Villmoare et al, Did the transition to complex societies in the Holocene drive a reduction in brain size? A reassessment of the DeSilva et al. (2021) hypothesis, Frontiers in Ecology and Evolution (2022). DOI: 10.3389/fevo.2022.963568
When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in Ants. Jeremy M. DeSilva et al. October 2021
Frontiers in Ecology and Evolution 9:742639 DOI:10.3389/fevo.2021.742639
