The skeleton of our primate ancestors developed for millions of years to support a creature that walked on all fours and had a relatively small head. Adjusting to an upright position was quite a challenge, especially when the scaffolding had to support an extra-large cranium. Humankind paid for its lofty vision and industrious hands with backaches and stiff necks. Women paid extra. An upright gait required narrower hips, constricting the birth canal – and this just when babies’ heads were getting bigger and bigger.
