The triple challenge of big-brained infants, a pelvis designed for walking upright, and a rotational delivery in which the baby emerges facing backward is not merely a contemporary circumstance.

• 大头婴儿、直立行走而设计的骨盆、绞的产道（以面朝产妇背面的姿势呱呱坠地）这三重困难不是现代产妇才面临的情境。