Two theories pertaining to human brain size have sprung up in the 2020s, and these actually contradict each other. One theory claims the human brain has shrunk in the past 3,000 years, while the other posits it in fact has not.
In a study by Jeremy M. DeSilva, James F. A. Traniello, Alexander G. Claxton, and Luke D. Fannin, it was found that in the last 3,000 years, there has been human brain size reduction. The study was published by Frontiers.
In the six million years since the appearance of Homo, human brain size has practically quadrupled. However, human brains are thought to have also seen a decrease in volume since the end of the last Ice Age. Researchers used change-point analysis to estimate the timing of changes in hominin brain evolution. They found that hominin brains experienced positive rate changes. These correlate with Homo’s early evolution as well as technological innovations evident in the archeological record.
The researchers used a dataset of 985 fossil and modern human crania. They surprisingly found that human brains increased in size 2.1 million years ago and again 1.5 million years ago during the Pleistocene. They then decreased in size around 3,000 years ago (Holocene).
Their analysis shows that this recent decrease in brain size may be the result of the externalization of knowledge and advantages of group-level decision-making. This is due in part to the advent of social systems of distributed knowledge and the storage and sharing of information.
Collective intelligence responsible for human brain shrinking
Experts explain that as humans live in small to large-sized social groups, multiple brains contribute to the emergence of collective intelligence. Although difficult to study in the distant past of Homo, the impacts of group size, social organization, collective intelligence, and other potential forces on brain evolution can be explained using ants as models.
There are many species of ants, living in a wide variety of ecological systems, and this rich diversity encompasses forms convergent to aspects of human sociality. These would include large group size, rural life histories, division of labor, and collective cognition. The specific insects that operate as societies, showing patterns that are similar to those of humans, provide a wide range of social systems to generate and test hypotheses concerning brain size enlargement or reduction. Observing the ants can aid in interpreting patterns of brain evolution identified in humans.
Although humans and ants represent very different routes in social and cognitive evolution, the insights ants offer can shed light to the selective forces that have an impact on brain size.
Describing collective cognition in his book Knowledge Illusion: Why We Never Think Alone, Dr. Steven Sloman, a psychologist and professor at Brown University, wrote: “We live in a community of knowledge. Everything we do depends on knowledge that is both inside our head as well as out in the world and in other people’s heads.”
New theory debunks brain decrease hypothesis
New research on the development of the human brain contradicts the theory that our brains have devolved in the past 3,000 years. Brian Villmoare, an anthropology professor at the University of Nevada, Las Vegas (UNLV), and Dr. Mark Grabowski, a paleoanthropologist and evolutionary biologist at the Liverpool John Moores University, argue that the size of the human brain did not change 3,000 years ago—or in fact 300,000 years ago, when the Jebel Irhoud Homo sapiens roamed the sands of Morocco.
According to Villmoare, it is impossible that the human brain shrank at a time when great leaps in human civilization were taken. From the works of Homer and Egypt’s New Kingdom to the development of Chinese script and the Olmec civilization, among other historical developments, there was a wealth of intellect and creativity.
Elaborating further in the UNLV website, the Professor said that after re-examining the dataset of the DeSilva et. al. theory, he found that he cannot identify any reduction in the human brain in the data. Regarding the habits of ants which exhibit certain similarities to those of humans, Villmoare further argues that what did or did not happen to other species’ brains is irrelevant to what happened to the human brain. He added that ants and humans are completely different species with completely different destinies.
The UNLV researchers say that agricultural developments and complex societies occurred at different times around the globe. This would mean there would be variation in the timing of skull changes seen across populations. Moreover, the number of crania used by DeSilva et. al. at the timeframe critical to the brain shrinkage theory is too small (23), and the specimen are taken from four different geographic locations, including England, China, Mali, and Algeria. These were areas where significant agricultural and societal changes took place at various times.
Furthermore, the UNLV team argues that the findings are skewed because more than half of the total 987 skulls examined represent only the last 100 years of a 9.8-million-year span of time. Therefore, they don’t reliably contribute to the understanding of how cranial size may have changed over time.
Scientific studies lead to conclusions that more often than not contradict each other. Further exhaustive studies need to be completed so as to safely assess what has happened to the human brain in the past 3,000 or even 300,000 years.