The human brain has been shrinking – and no-one quite knows why

The human brain has been shrinking over the last 100,000 years, and scientists are trying to understand why. Traditionally, our 'big brain' is thought to be what sets our species apart from other animals. Our capacity for thought and innovation allowed us to create the first art, invent the wheel, and even land on the Moon. However, studies show that this trend toward larger brains has reversed in Homo sapiens. In our species, average brain sizes have shrunk over the course of the last 100,000 years. For example, in a recent 2023 study, Ian Tattersall, a paleoanthropologist, tracked the braincase volumes of ancient hominins through time. He found that rapid brain expansion occurred independently in different species of hominins, and at different times across Asia, Europe, and Africa. However, the trend for brain enlargement over time was turned on its head with the arrival of modern humans. The skulls of men and women today are on average 12. 7% smaller than that of Homo sapiens who lived during the last ice age.