The idea that our brains are shrinking is generally not well received. For more than four decades, experts have largely ignored the hypothesis put forth repeatedly by a cohesive group of paleontologists. Now, the brain shrinkage hypothesis is being tested again, as a team from the University of Nevada, Las Vegas (UNLV) claims it does not hold up under scrutiny.
The debate really began last year when a paper prepared by paleoanthropologist Jeremy DeSilva and his colleagues was published, based on a comparison of human fossils with evolutionary patterns in ant colonies, suggesting that the human brain has shrunk in size by about four ping pong balls. Moreover, they claimed that this occurred just 3,000 years ago, which is indeed recent compared to other theories. Some scientists posited that human brains started to shrink sometime after the last Ice Age, which ended about 11,700 years ago. DeSilva's paper pinpointed the loss in brain size around the time complex human societies emerged.
As such, developing a smaller brain was proposed as it allowed for information to be stored in writing or distributed among others in society. In other words, our brains did not become less intelligent; they became more efficient.
This attractive theory garnered global attention, but not everyone was convinced. The UNLV team now claims to have uprooted the entire idea. Brian Filmowar, an anthropologist at UNLV, stated, "We reexamined the dataset from DeSilva et al. and found that human brain size has not changed for 30,000 years, and probably not for 300,000 years. In fact, based on this dataset, we cannot identify any decrease in brain size among modern humans over any period since the emergence of our species." Their findings are based on a new analysis of fossilized skulls, which differs from DeSilva's paper in several significant ways.
Of the 987 skulls analyzed by DeSilva and his team, only 23 skulls come from the critical time frame proposed for brain shrinkage. The dataset in the new study is much narrower to avoid distorting the results, focusing on modern humans from the past 300,000 years. This is because the UNLV researchers are not convinced that nearly 10 million years of early human history is relevant to an event purportedly occurring just 3,000 years ago.
Even within the last 300,000 years, most of the human fossils included in the UNLV analysis are dated within the last 10% of that time frame, making it difficult to find older fossils. To counter this uneven comparison, the researchers specifically honed in on human skull fossils from the last 30,000 years, creating a more natural distribution. Using DeSilva's own methods on the newly refined dataset, researchers found no significant point of change in human skull size for nearly 3,000 years.
Filmowar and his colleagues wrote: "Overall, our conclusion is that considering the dataset more suitable for the research question, human brain size has been remarkably stable over the past 300,000 years. Therefore, recent change hypotheses are not supported by evidence." DeSilva and his colleagues have not yet responded to the recent criticisms, but there is no doubt they will have something to say. In 2021, the researchers expressed hope that others would put their hypotheses to the test.
