Human brain size reduction: What do ant brains have to tell about it?

Debarati Basu, Makaut WB

The complex organ of the human body that forms the Central Nervous System (CNS) of the human body is the brain. A study is suggestive of the evolutions of the brain that will help us in better understanding the brain. The study shows the reduction in brain size dating approximately 3,000 years ago. The study utilizes ants as models demonstrating reasons for the increase or decrease in human brain size. Researchers are suggestive reduction in brain size is parallel to the evolution of collective intelligence within the human population. This study was published in Frontiers in Ecology and Evolution.

The nature of humanity can be understood by studying and comprehending the causes and results of brain evolution. The increase in the size of the human brain is evident and documented throughout evolutionary history. Reduction in brain size is since the Pleistocene which is not very appreciated. The actual reasons behind these changes and the duration of the changes are not known.

According to Dr. Jeremy DeSilva who is the co-author of this study and also an associate professor in the Anthropology department of Dartmouth College stated that one of the astonishing facts about human brains is that the present human species brain size is smaller compared to the brains of ancestral Pleistocene. But the reason behind this decrease in brain size is yet a big mystery.

A team of researchers from different fields of expertise are trying to solve this mystery by studying the historical human brain patterns, their evolution patterns, and then comparing their results with the ant societies for better understanding.

According to co-author Dr. James Traniello of Boston University, the collective work of a biological anthropologist and a behavioral ecologist and evolutionary neurobiologist on the evolution of the brain lead to the research on humans and ants that will help in better understanding and new possibilities present in nature.

Major points of the study:

A change-point analysis was applied by the researchers on a dataset consisting of 985 human fossils and modern human crania. The findings of this analysis showed that an increase in brain size took place during the Pleistocene from 2.1 million years ago and 1.5million years ago. The size reduction happened around 3,000yeatrs ago during Holocene. The size decrease of the brain happened more recently than it was estimated previously.

Traniello stated that many people know that human brain size was larger than their than our body size. The human brain size increased drastically during the period of evolutionary history but the decrease in brain size unexpectedly happened 3,000 years ago. 

The increase in the size of the brain happened during the early evolution of Homo and the technical development that followed after that. One example is finer diet and nutrition among large social groups. Researchers hypothesize decrease in brain size has a connection with ant societies.

Role of ants in human brain evolution:

According to Traniello ants can be utilized as diverse models in understanding the reason behind the increase or decrease in brain size’s relation to social life by using only the fossils.

The ant brain was utilized as a model and these computational models and was studied. The common garden ant Formica or Oecophylla weaver ant, Atta leafcutter ants size, structure, and energy use were studied that showed both labor division and cognition in group-level help in adaptive selection for variation in brain size. It can be explained in this way that within a social group of knowledge sharing or having specialists individuals in a particular task the adaptive tendency of the brain becomes efficient though there is a reduction in brain size.

Traniello stated that ant and human populations are divergent and have undergone a different course in social evolution. But ants and humans also have similarities as they share important aspects of social life including decision-making in groups and division of labor and also food production. These similarities play an important factor and can influence changes in human brain size.

Significance of the study:

A lot of energy is required by the brain for its functioning and smaller brains require lesser energy. Knowledge externalization in humans requires less energy to store huge information which played one of the major roles in the reduction of brain size.

Traniello further stated that the decrease in brain size is due to increasing dependency on collective intelligence. It can be explained by considering the objective that a group of people will be smarter than the smartest person present in that group also called as ‘wisdom of the crowds’.

Desilva said that he was looking forward to testing their hypothesis as soon as additional data are obtainable.

Also read: Lizard with unprecedented regeneration via CRISPR

Reference:

1. DeSilva, J. M., Traniello, J. F. A., Claxton, A. G., & Fannin, L. D. (2021). When and why did human brains decrease in size? A new change-point analysis and insights from brain evolution in ants. Frontiers in Ecology and Evolution, 9, 742639. https://doi.org/10.3389/fevo.2021.742639

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