Compared to Homo sapiens, a species that existed 100,000 years ago, modern humans have brains that are about 13% smaller, this is giving a definition Human Brain Shrinking. People commonly believe that our species’ “big brain” sets us apart from other animals. Human ingenuity has facilitated the creation of masterpieces, the invention of the wheel, and the remarkable achievement of landing on the moon. Indeed, in comparison to other animals of similar size, our brains are remarkably large. Over the course of six million years, the human brain has experienced a significant increase in size since our species diverged from chimpanzees. On the other hand, research indicates that the shift towards larger brains has actually reversed in Homo sapiens. Over the past 100,000 years, average size of the human brain shrinking.
American Museum of Natural History in New York City
Ian Tattersall, a paleoanthropologist and curator emeritus at the American Museum of Natural History in New York City, conducted a recent study in 2023 that analyzed the braincase volumes of ancient hominins over time. He began his study with the most ancient species and concluded with modern humans. Researchers discovered a rapid expansion of the brain in various species of hominins, occurring at different times across Asia, Europe, and Africa. Several species experienced brain growth over time, such as Australopithecus afarensis, Homo erectus, Homo heidelbergensis, and Homo neanderthalensis.
40 000 Years to the End of the Last Ice Age
We were on top of the food chain thanks to our superior brain size, which strengthened our belief. Evolution was unmistakably pointing towards our dominance over larger brains. This implies that possessing more intelligence equates to outsmarting the competition, which in turn leads to global dominance and enjoyment. Such a notion is logical and appealing, even if it’s not entirely accurate. Let’s travel back some 40 000 years to the end of the last ice age, when the thick pack of ice was slowly receding from mainland Europe. Our ancestors found their way to these new green pastures only to find that they weren’t the first ones there; indeed, they were Neanderthals. For thousands of years, they had been using these planes as hunting grounds. They had adapted to the rough climate and extreme conditions; they were magnificently superior to us in every aspect. They had stronger bones and muscles, could run faster, see and smell better, and yes, they even had a larger brain than we do, approximately 1,600 cubic centimeters versus our 1500 cubic centimeters.
Human Brain Shrinking Is Not a New Idea
Human brain shrinking is not a new idea and is not as controversial as Villmoare and Grabowski (2022) suggested. Von Bonin (1934) wrote, “There is a definite indication of a decrease, at least in Europe, within the last 10,000 or 20,000 years” in the human brain or human brain shrinking. Noted anthropologists Franz Weidenreich (1946) and Philip Tobias (1971) observed that modern human brain volumes are on average smaller than Pleistocene hominin crania. Schwidetzky (1976) discovered a decrease or shrinkage in the estimated number of “extraneurons” (following Jerison, 1963) since the Neolithic in parts of Europe. Wiercinski (1979) used linear measurements on 20 different populations in Europe, Africa, Asia, and Australia and found that the cranial dimensions were smaller in 17 of them. He came to the conclusion that this was a global phenomenon that happened after the Aurelian period.
Beals et al. (1984) used a set of 5,288 cranial capacities from 122 different global populations to find that brain size has been shrinking recently. They wrote, “We consider de-encephalization through the last 100,000 years as confirmed.” Henneberg (1988) evaluated primarily linear measurements taken on nearly 13,000 skulls and concluded that there had been a 10–17% decrease from the Mesolithic to modern times. We obtained most of these data from specimens from Europe, supplemented by additional skulls from northwest Africa and west Asia. Henneberg and Steyn (1993, 1995) identified a similar decrease in brain size in samples from sub-Saharan Africa and Japan. By 2004, Henneberg’s global study had exceeded 14,000 samples from 15 thousand years ago (ka) to the present day.
It’s getting better when it comes to brain size. Those same Homo sapiens, 40000 years ago, did have a larger brain than we do today. In other words, our brains aren’t becoming bigger; on the contrary, they are shrinking approximately 1400 cubic centimeters now compared to 1500 before, so what’s happening? Why did evolution reverse, and what does it all mean? Are we dumber than Neanderthal? Are we dumber than 40000 years ago? Brain size doesn’t always matter; otherwise, sperm whales and elephants would be ruling the old planets on second thoughts, and that might not have been such a bad idea. Now, brain size tends to vary according to body size; a stronger body with more muscles would need more brain volume to handle it, which partially explains the difference.
Theories on shrinking brains
Neanderthals have given rise to numerous theories about our shrinking brains. These theories range from dietary changes, such as consuming less protein due to agriculture, to the idea that larger heads make childbirth more challenging. Warmer climates cause less body mass to keep us warm. There is one theory I’m really fond of: the individual intelligence of the hormone neonatal versus the social intelligence of Homo sapiens. You see, Neanderthal was great; he was strong and smart enough to survive individually in a dangerous environment. He lived in small groups and thrived in a hostile environment. Homo sapiens, on the contrary, was way too weak, and on an individual level, we actually had no choice but to team up with others to have a chance to survive.
Limitations in Brain size Shrinking
Paradoxically, it is our weaknesses and limitations that paved the way to our success. So our brains turned us into truly social beings, with a strong emphasis on communication. All members of the Neanderthal clan were capable of performing all necessary tasks. As clan members died, we started to specialize, share, and rely even more on each other. Our higher communication skills led us to transfer knowledge from one generation to another, and you probably see where this is leading. As time went on, technology helped us share our knowledge even more, from books to radio to television and the internet. We’ve been relying more heavily on external sources and our own stalking device each time. While our brains are using them less and less, it’s needless to say that it costs way less energy to know how and where to find information than to remember the information itself. So our brain size is shrinking, and it will continue to do so, which means we’re becoming increasingly efficient and more social. Just remember that, as with more things in life, we use the equipment.
Deficiency of Vitamin B12 cause of Brian shrinking
Normal ageing causes the brain to shrink by an average of 1.9 percent every 10 years, beginning in young adulthood and becoming more prominent in your 60s. This is due to the natural decline of the number of grain cells with age. However, aging is not the only reason for our brains to shrink. Sleep disruptions and anxiety also contribute to the loss of brain volume. Healthy older adults with short sleep durations have significantly smaller brains. In addition to physical shrinkage, individuals with shorter sleep durations experience a 0.67 percent decrease in cognitive performance for every hour of reduced sleep duration. A deficiency in vitamin B12 can result in significant atrophy of the brain. One study showed that healthy volunteers with lowered but normal levels of vitamin B12 had more drain volume loss than healthy volunteers with higher levels. Implementing steps to improve B12 levels can prevent and often revers this type of atrophy.
Depression Is Associated With Brains Shrinkage
Depression is associated with shrinkage in the hippocampus, the region of the brain responsible for learning and memory. One study showed that depressed people have less brain tissue in their brain memory centers. The study revealed that the effects become more severe the longer an individual suffers from depression, and in people who received a diagnosis at an early age, several medical conditions can cause the brain to atrophy, including Alzheimer’s disease. Stroke, cerebral palsy, Huntington’s disease, and certain infections like HIV and encephalitis cause brain atrophy significantly faster and more detrimental than Alzheimer’s disease.
This article provides information on “Human Brains Shrinking: Evolutionary Insights into Human Brain Reduction.” I hope you will keep this list of information in mind. Best wishes for my readers.
Dr. Abid Hussain Nawaz
Post Doc, Ph.D, MPhil
References
DeSilva, J., Fannin, L., Cheney, I., Claxton, A., Ilieş, I., Kittelberger, J. & Traniello, J. (2023). Human brains have shrunk: the questions are when and why. Frontiers in Ecology and Evolution, 11, 1191274.
Villmoare, B., and Grabowski, M. (2022). Did the transition to complex societies in the Holocene drive a reduction in brain size? A reassessment of the DeSilva et al. (2021) hypothesis. Front. Ecol. Evol. 10:737.
von Bonin, G. (1934). On the size of man’s brain as indicated by skull capacity. J. Comp. Neurol. 59, 1–28. doi: 10.1002/cne.900590102
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Dear Dr.Abid
Thank you for your insightful article on human brain reduction! Your research and writing have shed light on a fascinating topic, sparking important discussions and new perspectives. Your contribution to the scientific community is invaluable. Keep sharing your expertise and inspiring new ideas.