The Shrinking Human Brain: What’s Causing It and Is It a Cause for Concern?

Jeremy DeSilva, a professor of paleoanthropology at Dartmouth College in the United States, asserted: “The commonly held belief that brain evolution follows a linear trajectory, where it continuously grows, reaches a plateau, and eventually ceases development, is erroneous. Contrarily, our brains have indeed diminished in size, losing brain tissue equivalent to the dimensions of a lime.” Calculations conducted by De Silva’s research team demonstrate that over the course of several millennia, the size of the human brain has rapidly declined by approximately 10%. Pertinent research papers have been published in the esteemed Swiss journal, Frontiers in Ecology and Evolution. Therefore, what precipitates this reduction in brain size? Will this shrinkage adversely impact brain function?

The concept of collective intelligence comes into play.

As per the calculations performed by De Silva’s research team, the average human brain capacity has essentially remained at around 1,450 milliliters over the past 150,000 years. However, within the past few thousand years, this value has experienced a swift decline of approximately 10%, reaching 150 milliliters.

Chris Stringer, a paleoanthropologist at the Natural History Museum in London, and neuroscientist Christopher Coker from the Allen Institute in the United States contend that books, personal devices, and the Internet function as reservoirs of information. It is plausible that these resources exacerbate the trend of brain shrinkage. Stringer elaborated, stating: “Our brains no longer necessitate the same level of exertion as they once did, thus they have diminished in size.” A report featured in the American magazine, “Discover,” highlights the reasons behind the decrease in human brain size. Arguably, the most compelling hypothesis posits that Homo sapiens underwent a process of “self-domestication.” This terminology originates from our comprehension of animal domestication. Domesticated species, such as sheep and dogs, exhibit numerous divergences in both physical and behavioral traits when compared to their wild ancestors. These differences include docility, diminished timidity, and smaller brain sizes.

Humans may have undergone a form of self-domestication as well: during the Stone Age, individuals who were cooperative and level-headed were more likely to survive and procreate than their aggressive counterparts. These proclivities are influenced by genetic factors, which also impact human physical characteristics, including body shape and brain size. Over time, this process of self-domestication within humans culminated in a reduction in brain size.

De Silva’s team speculates that collaboration within human social organizations has experienced a substantial increase within the past 3,000 years, thereby invoking the influence of collective intelligence. Living in groups enables individuals to solve problems more swiftly, efficiently, and accurately than if they were alone. As David Geary, a cognitive scientist at the University of Missouri, elucidates: The escalating complexity of societies implies that humans no longer need to master a wide array of survival skills characteristic of primitive societies. Consequently, certain functions of the human brain have gradually deteriorated, leading to a decline in brain capacity.

Functions are progressively advancing.

Will the reduction in human brain size impact its functions?

“The loss of a portion of the brain will not significantly impede its functionality.” Qiu Zilong, a researcher at the Songjiang Research Institute of Shanghai Jiao Tong University School of Medicine, asserts, “The human brain possesses a certain degree of redundancy. Even if a segment is lost, it will not exert a substantial influence on its overall function. The impact is minimal.”

Qiu further expounds from a neuroscientific perspective, postulating that the human brain does possess a certain amount of redundancy – an “idle space,” so to speak. If the loss does not involve a crucial component, it will not hinder the functioning of the entire brain. The evolution of the human brain is a gradual process, with significant transformations spanning tens of thousands of years. After examining human intelligence quotient (IQ), New Zealand scientist James Flynn discovered that throughout the course of continuous evolution, human IQ is consistently enhancing. This phenomenon has come to be known as the “Flynn effect.”