The Evolution of Human Brain Size, Religion, and the Decline in Cognitive Independence
For much of prehistory, the growth of the human brain and its relationship to body size—what scientists call encephalization—has been well-documented. This growth is believed to be the key to our advanced cognitive abilities. But in the last 50,000 years, both our bodies and our brains have begun to shrink. Some scientists suggest that for the last 25-50 thousand years, brain growth slowed, stopped, and then began to decline rapidly around 2,000 years ago.
Researchers have noted that the reduction in encephalization in modern humans, compared to our ancestors from the Holocene and Late Pleistocene, isn't just due to smaller bodies. When they adjust for body mass, the changes are proportional, suggesting other factors at play—like increased obesity and changes in lifestyle. A review of genome-wide studies hints at selective pressures that might have led to a reduction in brain mass, possibly more than 10%, over this period (DeSilva et al., 2021), (Stibel, 2021).
Brain Size Reduction During the Holocene
The most significant reductions in human brain size have occurred in the last 10,000 years, particularly during the Holocene. This reduction, tracked through skull size and brain volume, cannot be solely explained by genetics or smaller body sizes. It suggests that evolutionary pressures on the brain were influenced by energy needs, nutrition, and life history factors during early human development (Hawks, 2011).
The evidence shows that our brains began to shrink after the last Ice Age, with the most rapid changes occurring within the last 3,000 years. This shrinkage does not seem to be linked to body size reduction, agricultural diets, or self-domestication. Instead, it may be driven by the externalization of knowledge and the benefits of group decision-making. Social systems that promote collective thinking and knowledge-sharing may have played a significant role (DeSilva et al., 2021).
Religion’s Role in Cognitive Decline
As our brains shrank, organized religion grew. Religion, while unifying and morally guiding, has also been a force that suppresses independent thought. In medieval Brittany, people sought forgiveness through rituals tied to their ancestors’ beliefs, risking their ability to think independently. This mirrors the fate of Homo floresiensis, the "hobbits" of Flores, who failed to adapt and evolve intellectually, and so vanished (DeSilva et al., 2021).
Over the last 2,000 years, a period marked by the rise of organized religion, humans have lost about 10% of their brain volume. The link between the rise of religion and the decline in brain size suggests that as people leaned more on religious beliefs, they relied less on independent thought. Our brains, once our greatest tool for survival and innovation, are now at risk of wasting away if we continue to let rituals and dogma guide our thoughts instead of reason (DeSilva et al., 2023).
The Greeks and the Importance of Independent Thought
The sun rose over the African savannah. Our ancestors stood tall, their brains swelling with potential. But time is a cruel master. It gives and it takes away. For 50,000 years, our brains have been shrinking, like a receding tide, leaving behind smaller shells of our former selves. We were giants once, in mind if not in body.
The ice melted. The mammoths died. And our brains, those magnificent organs, began to melt too. In the last 3,000 years, this shrinkage accelerated. We lost knowledge like sand through an hourglass. We lost ourselves in the process.
Religion came like a warm blanket on a cold night. It brought rules, comfort, and a sense of belonging. But it took something too. It took our need to think, to question, to challenge. In medieval times, people prayed to stone and wood. They forgot to think. Like the little people of Flores, they could not adapt. They died, not in body, but in mind.
The Greeks knew better. They drank wine and argued philosophy under olive trees. Socrates, with his crooked nose and piercing eyes, said, "Think or die." Seneca, wrapped in his toga, warned us not to give our minds away. But we did not listen. We were too busy building empires and burning witches.
Now our brains are 10% smaller. We pray more. We think less. We are dying, not with a bang, but with a whimper. The scientists have numbers. They have charts. They show the brain getting smaller. They show religion getting bigger. It is not a coincidence. It is a tragedy (DeSilva et al., 2023).
Diversification
If you focus too much on developing traits instead of true professions, you’ll end up with workers who are little more than biorobots. They’ll be able to handle repetitive tasks, but they won’t think, they won’t innovate. Above them, you’ll have managers who look busy, who seem productive, but they’re just spinning wheels, adding no real value. This creates a cycle where real productivity drops, costs rise, and prices inflate. The basics become more expensive, and life gets harder. People feel helpless, unable to change things, trapped in a system that doesn’t reward real skill or hard work.
If you spend too much effort on developing generic traits rather than honing specific professions, you’ll end up with biorobots on the lower rungs of the value chain. These individuals will be capable only of performing repetitive, known operations. Meanwhile, at the managerial level, you’ll have sly, spineless people who only mimic productivity, giving the appearance of efficiency without adding real value. This approach leads to cognitive helplessness, where workers and managers alike lose the ability to think critically or innovate. The end result is a reduction in actual productivity, which drives up costs and inflates the prices of basic goods. As prices rise and quality declines, the overall standard of living falls.
The solution lies in education, but there’s a catch. If education itself becomes too automated, too focused on rote learning, you risk creating the same problem in the classroom as in the workplace. Students trained only to follow instructions without understanding the principles behind them will enter the workforce as the very biorobots we sought to avoid. Education should focus on fostering critical thinking, creativity, wide modular knowledge allowing to quickly get profound understanding in specific fields. This way, future generations will be equipped not just to participate in the economy, but to lead and innovate within it.
We used to survive by thinking, by outwitting the saber-toothed tiger and the wooly rhinoceros. Now we survive by believing, by following, by obeying. It is easier. It is more dangerous. The brain was our best tool. Now it is rusting. We must use it or lose it.
To live is to think. To stop thinking is to start dying. We must question the priest, the politician, the professor. We must challenge the book, the law, the custom. We must think until our heads hurt and our hearts race.
If we do not, we will fade, like the people of Flores, like the Neanderthals, like all those who could not adapt. We will become a footnote in the book of life, a cautionary tale for whatever species comes after us.
The evolution of human brain size over the past 2,000 years has been shaped by a complex mix of evolutionary, environmental, and social forces. The rise of organized religion, while promoting social cohesion, may have also led to a decline in independent thought and cognitive ability, paralleling the observed reduction in brain size. To keep the essence of what makes us human, we must continue to question, think, and challenge the norms. We must think to live. We must think to be human. We must think to survive. The future is not written. It is thought. Let us think it well. Let us think it hard. Let us think until we become what we were meant to be. What we can be. What we must be.
Religions need to focus less on rituals and more on the core moral values that matter. The ceremonies, the rituals, the grand buildings—they should all take a back seat to what truly counts: teaching people to live good lives, to help one another, to be kind. Religion should be more about action and less about pomp. And it’s time to break up the power held by religious institutions. Decentralize them, let local communities take the lead. Make them answerable not just to a higher power, but to the people they serve. Strip away their privileges—the tax breaks, the special treatment, their parking lots. Donations to churches should not be called charity unless they’re truly helping those in need. It's about fairness, about making sure that religion isn’t just another institution hoarding wealth and power, but a force for good in the world (McKay, 2015) (STR, 2017) (Humans and Nature, 2017) (OpenTextBC, n.d.).
To counteract the risks of improper diversification, education must be leveraged effectively. However, care must be taken to avoid the pitfalls of robotization in education itself. Over-reliance on automated teaching methods and rote learning can further entrench the problems of a mechanized workforce, where students are trained to follow instructions without understanding the underlying principles. Education should focus on fostering critical thinking, creativity, and deep knowledge in specific fields, ensuring that future generations are equipped not just to participate in the economy but to lead and innovate within it (Investopedia, 2024), (Investopedia, n.d.), (HBR, 1997). For more on the diversification dilemma please see my article https://www.saklakov.com/blog/beyond-the-bet-how-to-win-or-lose-in-the-game-of-diversification .
The sun sets on the savannah. Our descendants stand tall, their brains swelling with potential once again. Time is a cruel master, but we are its masters now. We think, therefore we are. We think, therefore we will be.
References
- DeSilva et al., 2023 - "Human brains have shrunk: the questions are when and why"
- DeSilva et al., 2021 - "When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in Ants"
- Hawks, 2011 - "Selection for smaller brains in Holocene human evolution"
- Stibel, 2021 - "Decreases in Brain Size and Encephalization in Anatomically Modern Humans"
- McKay, R. (2015). Religion and Morality. PMC. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4345965/
- STR. (2017). Do You Need Religion to Have Morals? Stand to Reason. Retrieved from https://www.str.org/w/do-you-need-religion-to-have-morals-
- Humans and Nature. (2017). From Ritual to Morality: Where Deeds and Words Meet. Humans and Nature. Retrieved from https://humansandnature.org/from-ritual-to-morality-where-deeds-and-words-meet/
- OpenTextBC. (n.d.). Chapter 15. Religion. Introduction to Sociology. Retrieved from https://opentextbc.ca/introductiontosociology/chapter/chapter-15-religion/
- Investopedia - The Dangers of Over-Diversifying Your Portfolio
- Investopedia - Labor Productivity: What It Is, Calculation, and How to Improve It
- HBR - To Diversify or Not To Diversify