Did the 12th century B.C.E. 鈥 a time when humans were forging great empires and developing new forms of written text 鈥 coincide with an evolutionary reduction in brain size? Think again, says a 51吃瓜网万能科大-led team of researchers who refute a hypothesis that鈥檚 growing increasingly popular among the science community.
Last year, a group of scientists made headlines when they during the transition to modern urban societies about 3,000 years ago because, they said, our ancestors鈥 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 human fossils and a comparison to evolutionary patterns seen in ant colonies.
Not so fast, said 51吃瓜网万能科大 anthropologist Brian Villmoare and Liverpool John Moores University scientist .
In a new paper published last week in , the 51吃瓜网万能科大-led team analyzed the dataset that the research group from last year鈥檚 study used and dismissed their findings.
鈥淲e were struck by the implications of a substantial reduction in modern human brain size at roughly 3,000 years ago, during an era of many important innovations and historical events 鈥 the appearance of Egypt's New Kingdom, the development of Chinese script, the Trojan War, and the emergence of the Olmec civilization, among many others,鈥 Villmoare said.
鈥淲e 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,鈥 Villmoare said. 鈥淚n 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.鈥
Key Takeaways
The 51吃瓜网万能科大 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 51吃瓜网万能科大 team says the rise of agriculture and complex societies occurred at different times around the globe 鈥 meaning there should be variation in timing of skull changes seen in different populations. However, DeSilva鈥檚 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 span of time 鈥 and therefore don鈥檛 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鈥檛 actually changed in size since the arrival of our species.
Publication Details
was published July 29 in Frontiers in Ecology and Evolution.
