Human brains tripled in size mostly within the last two million years

Evidence

Compared to those of other animals, our brains are big, dense, and groovy. While we don’t have the biggest brains in the natural world—whales and elephants beat us—we do have the most cortical interconnections and the highest degree of cortical folding. Cortical folding produces that “crumpled wad of paper” (groovy) appearance that particularly characterizes human brains. But that’s just the beginning of our oddities. Our brains evolved from the size of a chimpanzee’s, at roughly 350 cm3 , to 1350 cm3 in about 5 million years. Most of that expansion, from about 500 cm3 upward, took place only in about the last 2 million years. That’s fast in genetic evolutionary terms. — Joseph Henrich, The Secret of Our Success, 212

Categorization

• XREF: connects to: Collective brain size, not individual intelligence, may have driven Neanderthal replacement — Joseph Henrich, The Secret of Our Success: How Culture…, 736; Brain expansion via longer lifespans makes species extinction-prone — Joseph Henrich, The Secret of Our Success: How Culture…, 977; Using tools led to the survival and proliferation of larger-brained humans. — Neil MacGregor, A History of the World in 100 Objects, 84

Broader Connections

• Using tools led to the survival and proliferation of larger-brained humans. #expands (0.85) — Neil MacGregor, A History of the World in 100 Objects, 84
• Brain expansion via longer lifespans makes species extinction-prone #expands (0.78) — Joseph Henrich, The Secret of Our Success, 977
• Collective brain size, not individual intelligence, may have driven Neanderthal replacement #complicates (0.75) — Joseph Henrich, The Secret of Our Success, 736