The human mind can carry out cognitive tasks that other animals cannot, such as using language, envisioning the distant future and inferring what other people are thinking.
The human brain is exceptional, too. At 3 pounds, it is gigantic relative to our body size. Our closest living relatives, chimpanzees, have brains one-third as big.
Scientists have long suspected that our big brain and powerful mind are intimately connected. Starting about 3 million years ago, fossils of our ancient relatives record a huge increase in brain size. Once that cranial growth began, our forerunners started leaving behind signs of increasingly sophisticated minds, such as stone tools and cave paintings.
But scientists have long struggled to understand how a simple increase in size could lead to the evolution of those faculties. Two Harvard neuroscientists, Randy Buckner and Fenna Krienen, have offered a powerful, simple explanation.
In our smaller-brained ancestors, the researchers said, neurons were tightly tethered in a relatively simple pattern of connections. When our ancestors’ brains expanded, those tethers ripped apart, enabling our neurons to form new circuits.