Did human brains shrink 3,000 years ago, downsizing by an amount equal to around four ping-pong balls?

Humans take a lot of pride in their brains. We like to think we are an intelligent species, and even though size isn't everything, our noggins are some of the largest nature has to offer.

For decades, scientists have heralded the idea that human brains have increased in size over the course of history, evolving in modern humans be much larger than that of our Neanderthal cousins. In October 2021, DeSilva et al., seemingly added more evidence to this hypothesis with a paper that concluded the human brain shrank during the transition to modern urban societies about 3,000 years ago. And while this supported previous literature, the research did establish a new timeline—marking brain decrease as late as the last Ice Age.

Anthropologists believe that brain size has remained dynamic in size. It nearly quadrupled in the six million years since Homo last shared a common ancestor with chimpanzees, but human brains are thought to have decreased in volume since the end of the last Ice Age.

According to the scientific consensus, in the last 6 million years, the size of the human brain increased roughly three times in parallel with the appearance of various new, increasingly complex activities, and then reached its maximum 10-15 thousand years ago, which is considered yesterday in the evolutionary time scale.

The organ's size has actually held steady over the past 300,000 years, according to new research that reassessed data on brain evolution.

The contention the human brain shrank sharply around 3,000 years ago, coinciding with the establishment of cities, has captured popular and scientific imagination, but new evidence suggests it never happened.

The 12th century BC, when humans were forging great empires and developing new forms of written text, did not coincide with an evolutionary reduction in brain size.