We know, and this is quite intuitive, that the human brain has grown throughout our evolutionary history . However, a more unknown fact is that our thinking organ has also decreased in size since the Pleistocene, and until now the reason was not known.
Studying ants as models that can illustrate the causes of changes in brain size, a team of researchers has hypothesized that their contraction parallels the expansion of collective intelligence in human societies. The results are published in the journal Frontiers in Ecology and Evolution and provide new clues about the evolution of this complex organ and about our own history as humanity.
The researchers applied a switch point analysis to a data set of 985 fossil and modern human skulls. They found that human brains increased in size 2.1 million years ago and 1.5 million years ago, during the Pleistocene, but decreased in size about 3,000 years ago (Holocene).
“Most people are aware that humans have unusually large brains, significantly larger than predicted from our body size. In our evolutionary history, the size of the human brain increased dramatically, ”explains James Traniello, a researcher at Boston University and a co-author of the study. ” The reduction in the size of the human brain 3,000 years ago was unexpected .” The timing of the increase in size coincides with what was previously known about the early evolution of Homo and the technical advances that led, for example, to better diet and nutrition and larger social groups. Regarding the decrease, the team of researchers proposes a new hypothesis:
“We propose that ants can provide various models to understand why brains can increase or decrease in size due to social life. Understanding why brains increase or decrease is difficult to study using only fossils, ”explains Traniello.
The study of models and computational patterns of the worker ant brain size, structure and energy use in some ant clades, such as the weaver ant Oecophylla , the leaf-cutter ants Atta or the common garden ant Formica , showed that group-level cognition and division of labor can influence adaptive variation in brain size. This means that within a social group where knowledge is shared or individuals are specialists in certain tasks, brains can adapt to be more efficient, such as decreasing in size .
“Ant and human societies are very different and have taken different routes in social evolution,” explains the researcher. “However, ants also share with humans important aspects of social life such as group decision-making and the division of labor, as well as the production of their own food (agriculture). These similarities can broadly inform us of the factors that can influence changes in the size of the human brain. “
Consume less energy and be more efficient
Brains use a lot of energy and smaller brains use less energy. The externalization of knowledge in human societies, which means that less energy is needed to store much information as individuals, may have favored a decrease in the size of the brain.
“We propose that this decline was due to a greater reliance on collective intelligence, the idea that a group of people is smarter than the smartest person in the group, often called the ‘wisdom of crowds,'” concludes the expert. .
