The Human Brain Did Not Shrink 3,000 Years Ago

Author: University of Nevada, Las Vegas
Published: 6 Aug 2022 - Updated: 22 Aug 2026
Publication Details: Peer-Reviewed | Findings

Table of Contents:
Synopsis - Definition - Overview - FAQs - Insights, Updates - Related Content

Synopsis

This research reports on a University of Nevada, Las Vegas led study, published in the peer-reviewed journal Frontiers in Ecology and Evolution, that disputes a widely circulated claim that the human brain shrank during the shift to complex urban societies roughly 3,000 years ago. Anthropologist Brian Villmoare and Liverpool John Moores University scientist Mark Grabowski reanalyzed the same dataset behind the 2021 DeSilva et al. hypothesis and concluded that human brain size has not changed in 30,000 years, and likely not in 300,000 years, identifying no measurable reduction at any point since our species began. This matters to anthropologists, evolutionary biologists, educators, students, and general readers because the original idea had gained real traction and shaped assumptions about how society and cognition co-evolved. The authors point to serious sampling problems in the earlier work, noting that agriculture and complex societies arose at different times worldwide and that the dataset leaned heavily on recent specimens, with more than half of the 987 skulls representing only the past century of a 9.8-million-year span. Grounded in direct examination of the original evidence and clearly explained, the findings offer a reliable correction that helps a broad audience, including seniors and people with disabilities interested in brain science, understand how researchers test and revise claims about human evolution.*

At a Glance

• 1 - The disputed 2021 hypothesis drew its reasoning from evolutionary patterns observed in ant colonies. It proposed that storing information externally within social groups lowered our need for large brains.
• 2 - The original dataset sampled only 23 crania from the window critical to the shrinkage claim. It grouped together specimens from England, China, Mali, and Algeria despite their different histories.
• 3 - The proposed shrinkage was said to coincide with the New Kingdom of Egypt, the development of Chinese script, the Trojan War, and the rise of the Olmec civilization. Villmoare noted these were eras of major innovation rather than cognitive decline.
• 4 - Because agriculture and complex societies emerged at different times across the globe, the timing of any skull changes should vary between populations. The absence of that expected variation undercuts a single 3,000-year turning point for brain reduction.

Topic Definition

Human Brain

The human brain is the central organ of the human nervous system, and with the spinal cord makes up the central nervous system. The brain consists of the cerebrum, the brainstem, and the cerebellum. It controls most of the body's activities, processing, integrating, and coordinating the information it receives from the sense organs and making decisions about the instructions sent to the rest of the body. The human brain can be divided into three basic units: the forebrain, the midbrain, and the hindbrain. Weighing about 3 pounds in the average adult, the brain is about 60% fat. The remaining 40% is a combination of water, protein, carbohydrates, and salts. The brain itself is not a muscle. It contains blood vessels and nerves, including neurons and glial cells. For decades, brain scientists have noticed that male brains tend to have slightly higher total brain volume than female ones, even when corrected for males' larger average body size. Scientists have learned more about the brain in the last ten years than in all previous centuries because of the accelerating pace of research in neurological and behavioral science and the development of new research techniques.

Overview

Did the 12th century B.C.E., when humans were forging great empires and developing new forms of written text, coincide with an evolutionary reduction in human brain size? Think again, says a UNLV-led team of researchers who refute a hypothesis that's growing increasingly popular among the science community.

Last year, a group of scientists made headlines when they concluded that the human brain shrank during the transition to modern urban societies about 3,000 years ago because, they said, our ancestors' ability to store information externally in social groups decreased our need to maintain large brains. Their hypothesis, which explored decades-old ideas on the evolutionary reduction of modern human brain size, was based on a comparison to evolutionary patterns seen in ant colonies.

Not so fast, said UNLV anthropologist Brian Villmoare and Liverpool John Moores University scientist Mark Grabowski.

In a new paper published last week in Frontiers in Ecology and Evolution, the UNLV-led team analyzed the dataset that the research group from last year's study used and dismissed their findings.

"We were struck by the implications of a substantial reduction in modern human brain size roughly 3,000 years ago, during an era of many important innovations and historical events - the appearance of Egypt's the New Kingdom, the development of Chinese script, the Trojan War, and the emergence of the Olmec civilization, among many others," Villmoare said.

"We re-examined the dataset from DeSilva et al. and found that human brain size has not changed in 30,000 years, and probably not in 300,000 years," Villmoare said. "In fact, based on this dataset, we can identify no reduction in brain size in modern humans over any time period since the origins of our species."

Key Takeaways The UNLV research team questioned several of the hypotheses that DeSilva et al. gleaned from a dataset of nearly 1,000 early human fossil and museum specimens, including:

• The UNLV team says the rise of agriculture and complex societies occurred at different times around the globe - meaning there should be variation in the timing of skull changes seen in different populations. However, DeSilva's dataset sampled only 23 crania from the timeframe critical to the brain shrinkage hypothesis and lumped together specimens from locations including England, China, Mali, and Algeria.
• The dataset is heavily skewed because more than half of the 987 skulls examined represent only the last 100 years of a 9.8-million-year period - and therefore don't give scientists a good idea of how much cranial size has changed over time.
• Multiple hypotheses on causes of reduction in modern human brain size need to be reassessed if human brains haven't actually changed in size since the arrival of our species.

What Occurs in The Brain At Time of Death - Research reveals brain oscillations associated with memory retrieval alter in the moments before death, suggesting our brain may replay significant life events just before we die.

Frequently Asked Questions

NOTE: Researched FAQs by Disabled World (DW)

Who conducted the study that disputes the brain shrinkage claim

The reassessment was led by University of Nevada, Las Vegas anthropologist Brian Villmoare along with Mark Grabowski of Liverpool John Moores University.

What was the original brain shrinkage hypothesis

A 2021 study proposed that the human brain grew smaller about 3,000 years ago as complex societies let people store knowledge externally, reducing the need for large individual brains.

Where was the new rebuttal published

The rebuttal appeared in the peer-reviewed journal Frontiers in Ecology and Evolution, where the team reanalyzed the same dataset used in the earlier study.

How large was the dataset the researchers examined

The dataset contained nearly 1,000 early human fossil and museum specimens, though the team found its coverage across time was very uneven.

Why does the sampling of skulls matter to the conclusion

More than half of the 987 skulls represented only the last 100 years of a 9.8-million-year span, which skews the picture of how cranial size changed over deep time.

Does the human brain differ in size between the sexes

Researchers have long observed that male brains tend to have slightly larger total volume than female brains, even after adjusting for larger average body size in males.

How far back does the study say brain size held steady

The team concluded that human brain size has not changed in 30,000 years and probably not in 300,000 years, finding no reduction since our species began.

What does this mean for other theories about brain evolution

If brain size has stayed constant, then the various hypotheses built to explain a supposed shrinkage need to be reassessed or set aside.

Insights, Analysis, and Developments

Editorial Note: The strength of this rebuttal lies less in new fossils than in a careful second look at old numbers, a reminder that a striking dataset can mislead when its sampling is uneven. If human brain size truly held steady since the origin of our species, then the broader family of theories built to explain a supposed shrinkage, including ideas about externalized memory and social offloading, may need to be set aside or rethought from the ground up. There is also a quiet lesson here about how popular science claims travel, since the 3,000-year figure captured headlines and public imagination well before it was stress-tested, and about the value of researchers who take the time to check whether a compelling story actually holds up against the evidence that produced it.*

Attribution/Source(s): This peer reviewed publication was selected for publishing by the editors of Disabled World (DW) due to its relevance to the disability community. Originally authored by University of Nevada, Las Vegas and published on 6 Aug 2022, this content may have been edited for style, clarity, or brevity.

* Editorial additions by Ian C. Langtree.