Scientists Say Our Brains Are 13% Smaller Than They Were 100,000 Years Ago

Humans are undoubtedly smarter than they were 100,000 years ago. But that statement is not actually accurate, as most people would think. The reality is we have accumulated so much knowledge and complex technologies that made our primitive ancestors look dumber than we do.

Studies have shown that human anatomy, even from the past, has evidence that proves that the cognitive capacity for using tools and complex thoughts is already present. In other words, the thing that changed the most for modern humans to look and feel like they are smarter is not the fundamental intelligence of the human brain, because in reality, it actually shrank by about 13%.

The Surprising Shrink

Researchers from Cornell University have found that human brain size is declining over time and has possibly peaked during the Ice Age, approximately 100,000 years ago. They have studied the skulls of fossil remains of humans and compared their measurements to each other, including the modern human skull.

They have found out that the decline in size of our brains, which is estimated to be about 13% from 100,000 years ago, was an evolutionary response to changes in our environment and the way we lived. The shrinkage was estimated to have begun significantly about 10,000 years ago, during the Holocene era.

Read more: Cornell University

Why Are Our Brains Shrinking?

The Mystery of Shrinking Brains in Modern Humans | Why Is It Happening?

The Holocene era is the time when our ancestors transitioned from hunter-gatherers to agricultural farmers. It is approximately 11,700 years ago when they first made this change.

The factor that affected this decision the most is probably the change in climate and the end of the Ice age. A warmer and more stable climate is ideal for farming and agriculture, and it coincides with the development of human civilization as we know it. They started creating cities with a population close to a million, giving rise to empires and complex human settlements.

This all points to the leading theory on why our brain shrank, because we have less need to do it all. The tasks can be divided and decentralized, reducing the necessity for humans to have large individual brain power. Some scientists also think our diet from the new agricultural foods from this era has reduced the evolutionary pressures for a larger brain.

Read more: University of Cambridge

Energy and Lifestyle Changes

In human anatomy, our brains are actually one of the most expensive body parts to maintain. It consumes so much energy, roughly 20% of our energy, even at rest. So during the Holocone, the evolutionary process probably chose a brain easier to maintain and consumes less energy, since these would be the people likely to survive that era.

The modern lifestyle, where we have tools, writings for storage of knowledge instead of brains, and a network of people in our community that could do jobs we couldn’t all do, has probably affected the shrinkage of human brain size. This is because there is no selective benefit or reduced benefit for having and sustaining larger brains.

What It Tells Us About Humanity

What this tells us about humanity is that we are not necessarily smarter than our ancestors, if we are just talking about the pure cognitive abilities of our brains. It is just that we have accumulated and stored so much knowledge that our ancestors did not have, along with systems all designed to help our brains function at their best.

It also shows that we are an evolutionary creature that will adapt and change based on our environments and needs for survival. Whether that is shrinking our brains to be more efficient, as we actually are compared to earlier humans, or maintaining what nature and our bodies think will help us survive longer and thrive better.

The Evolution of the Human Brain

Author's Final Thoughts

Brain size is not a direct measure of intelligence; this is all much more complicated than comparing our skulls to earlier humans. Although our brains are much smaller, we are more efficient and optimized for today’s challenges. Understanding this trend helps appreciate how far we have come and how much more we are going to change in order to adapt.

Read more: Scientists Once Thought a Supervolcano 74,000 Years Ago Almost Wiped Us Out — The Eruption Was Still One of the Biggest Ever

References & Further Reading

DeSilva, J. M., et al. (2021). When and why did human brains decrease in size? A new change-point analysis of hominin brain size evolution. Frontiers in Ecology & Evolution. https://www.frontiersin.org/articles/10.3389/fevo.2021.742639/full

Villmoare, B., & 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. Frontiers in Ecology & Evolution. https://www.frontiersin.org/articles/10.3389/fevo.2022.963568/full

DeSilva, J. M., et al. (2023). Human brains have shrunk: the questions are when and why. Frontiers in Ecology & Evolution. https://www.frontiersin.org/articles/10.3389/fevo.2023.1191274/full

Stibel, J. M. (2022). Climate change influences brain size in humans. Brain, Behavior and Evolution. https://pmc.ncbi.nlm.nih.gov/articles/PMC10064386/

Neubauer, S., Hublin, J.-J., & Gunz, P. (2018). The evolution of modern human brain shape. Proceedings of the National Academy of Sciences. https://pmc.ncbi.nlm.nih.gov/articles/PMC5783678/