Around 3,000 years ago, the size of the human brain shrunk considerably. A new study suggests that, as in ants, this shrinkage is linked to the expansion of collective intelligence in human societies.
- Although gradually increasing over time, the size of the human brain began to shrink around 3,000 years ago.
- This decrease in brain volume coincides with the enlargement of social groups: by promoting collective intelligence, humans have seen the size of their brain decrease.
- This characteristic has also favored the survival of the human species: by becoming smaller, the brain has become more efficient and requires less energy.
The evolution of man, and more particularly that of his brain, is at the heart of the work of paleoanthropologists to better understand the nature of humanity. Until Neanderthal, the size of the brain gradually increased in relation to the size of the body, reaching 1520 cm3.
But a mystery remains. Over the past millennia, the size of the brain has regressed. “A startling fact about humans today is that our brains are smaller than those of our Pleistocene ancestors. Why our brain size decreased is a great mystery to anthropologists,” explains Dr Jeremy DeSilva, from Dartmouth College (USA).
In a study published in Frontiers in Ecology and Evolution, the researcher and his interdisciplinary team shed new light on the human brain and its evolution. By bringing together research on humans and ants, they may have found the answer.
A smaller brain for about 3,000 years
The researchers analyzed the change points to a dataset comprising 985 fossil and modern human skulls. They found that human brain size increased 2.1 million years ago and 1.5 million years ago, during the Pleistocene, but decreased around 3,000 years ago (Holocene ), which is more recent than previous estimates.
The timing of the increase in size coincides with what is already known about the beginnings of the evolution of Homo and the technical advances that have made it possible, for example, to improve food and nutrition and expand social groups.
And it is precisely this widening of social groups that would also be at the origin of the decrease in the size of the human brain.
A decrease linked to the emergence of the social group
To put forward this hypothesis, the researchers base themselves on clues within ant societies. “We propose that ants may provide various models for understanding why brains may increase or decrease in size due to social life”explains Dr. James Traniello, of Boston University, co-author of the article.
The team used computer models to analyze patterns of worker ant brain size, structure and energy use. The results showed that group-level cognition and division of labor can lead to adaptive variation in brain size. This means that within a social group where knowledge is shared or individuals are specialized in certain tasks, brains can adapt to become more efficient, and thus shrink in size.
“Ant societies and human societies are very different and have taken different paths in social evolution, recalls Dr. Traniello. Nevertheless, ants share important aspects of social life with humans, such as group decision-making and the division of labor, as well as the production of their own food. These similarities can tell us a great deal about the factors that may influence changes in human brain size.”
This decrease in the size of the human brain is therefore due, according to the researchers, to the use of collective intelligence. The externalization of knowledge in human societies, requires less energy to store a lot of information as individuals, which has promoted a decrease in brain size. And Dr. Traniello quotes “the wisdom of crowds”: “A group of people is smarter than the smartest person in the group.”
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