Brains start growing
Hominin cranial capacity begins a climb that will triple it, and something has to pay for it.
- When
- —
- Duration
- 1.2 million years
- Known to
- ± 100 thousand years
- Era
- Early Pleistocene, Quaternary
From about 2 million years ago brain size increases steadily across the Homo lineage. Brain tissue is metabolically ruinous — in modern humans it is 2 per cent of body mass and 20 per cent of resting energy use — so the increase requires a diet dense enough to fund it. The expensive tissue hypothesis notes that human guts are correspondingly small: higher-quality food, obtained with tools and later cooking, allowed the gut to shrink and released the energy the brain needed.