The large size of the human brain is what makes us (probably) the most intelligent beings on Earth, but new research surprisingly reveals that our brains may have shrunk slowly since about 3,000 years ago. Are we getting less smart? Scientists are not yet ready to say this, but they have found a possible answer to the mystery of brain size through the study of ants and the use of collective intelligence in their social organizations.
Researchers have found that throughout much of human evolutionary history, our brains continue to grow. In fact, if we count our last common ancestors with chimpanzees six million years ago, the size of the human brain has almost quadrupled. This was due in part to improved diet and nutrition for the elderly. Cro Magnons, Homo sapiens, who had the largest brain in history, were alive 20,000 to 30,000 years ago. But like recent study from scientists at the universities of Dartmouth and Boston points out that about 3,000 years ago, in the current Holocene geological era, our brains began to shrink.
“It is a surprising fact for people today that our brains are smaller than the brains of our Pleistocene ancestors.” shared the co-author of the study, Dr. Jeremy DeSilva of Dartmouth College, adding, “Why our brains have shrunk in size is a big mystery to anthropologists.”
When did the human brain start to shrink?
Scientists have found that the trend to shrink the brain began much earlier than some previous observers of the phenomenon have suggested. By analyzing a set of data from 985 fossil and modern human skulls, the researchers found periods of brain growth. 2.1 and 1.5 million years ago, but also defined the period about 3,000 years ago as the time when the size of the brain began to decrease. Previous research estimated that over the past 20,000 years, the average volume of the human brain has increased from 1,500 cubic centimeters (cc) to 1,350 cc – shrinking by about 150 cc, or 10% (the size of a tennis ball, as commentators comment). indicated).
“Most people are aware that humans have unusually large brains – significantly larger than our body size predicts. In our deep evolutionary history, the size of the human brain has increased dramatically.” said the other co-author of the study, James Traniello of Boston University. “The reduction in the size of the human brain 3,000 years ago was unexpected.”
Why did the brains start to shrink?
The big question, of course, is, “Why is our evolution going backwards?” The interdisciplinary research team that included biological anthropologist, behavioral ecologist and evolutionary neurobiologist, write in the study that their dating techniques don’t do it “support hypotheses about the reduction in brain size as a by-product of the reduction in body size as a result of switching to an agricultural diet or as a result of self-examination.
In fact, previous assumptions about contraction have suggested that as the average human body shrinks over the millennia, our brains also begin to shrink. A larger body should support a larger nervous system. Another aspect of this is that shrinking bodies would encourage smaller pelvic sizes in women. writes Scientific American, and therefore selection can encourage the birth of babies with smaller heads.
But the team behind the new study found no evidence for these explanations. So what did they suggest as the reason why the brains of Homo sapiens began to shrink?
Scientists suggest that the reason we don’t need brains of the same size lies in the creation of our social systems, which favor the distributed collection and sharing of knowledge and information, while offering advantages in group-level decision-making. Because brains use a lot of energy, being able to draw on the knowledge gathered in a larger society would require less individual brain energy to be expended to store and process information. So a smaller brain could do the job just as well.
But what happened about 3,000 years ago that specifically affected our brains? Interestingly, researchers also suggest that the advent of writing about 5,000 years ago may have had a marked effect on the “neural architectures” of individual human brains by increasing the power of group knowledge. Decision making by an increasingly connected group can lead to “Adaptive group responses that went beyond the cognitive accuracy and speed of individual decisions and had implications for fitness.” This could lead to a reduction in the size of the human brain “as a result of saving metabolic costs”.
What can ants teach us?
Unexpectedly, the researchers came to their conclusions by studying ants. As scientists write in their paper, “People live in social groups in which multiple brains contribute to the emergence of collective intelligence.” While understanding the historical forces influencing human brain evolution is a complex endeavor, using only fossils as evidence, researchers examine the communities of ants.
“The remarkable ecological diversity of ants and their species richness encompasses forms converging in aspects of human sociality, including the size of the group, the history of agricultural life, the division of labor and collective knowledge “, explain the scientists in study. The range of social systems in ant societies has allowed them to test hypotheses and come up with insights that provide an overview of how selective forces can affect brain size.
The research team focused specifically to create computational models that represent models of worker ant brain size and energy use, considering groups of weaver ants Oecophylla, leaf-cutting ants and common formica. What they found was that collective intelligence and the division of labor influenced variations in brain size. In a group with shared knowledge and individual specialization in certain tasks, the brains are likely to adapt in the name of efficiency, therefore decreasing in size.
“Ants and human societies are very different and have taken different paths in social evolution.” Traniello shared. “However, ants share with people important aspects of social life, such as group decision-making and division of labor, as well as their own food production (agriculture). These similarities can generally tell us about the factors that can affect changes in the size of the human brain. “
Although this study has no definitive answers as to what has affected the changing volume of our brains, the new modeling is a fascinating step forward in approaching a more complete picture of our evolutionary transformation.