Pregnancy Is a War; Birth Is a Cease-Fire

Evolutionarily speaking, every human is a bit of a preemie. The nine months most babies spend in the womb are enough for them to be born with open eyes, functional ears, and a few useful reflexes—but not the ability to stand, sprint, climb, or grasp onto their parents’ limbs. Compared with other primates, our offspring are wobbly and inept; they’d probably get their butts kicked by infant lemurs, gorillas, and even tiny tarsiers, which all come out more fully formed. Think of it this way: Researchers have estimated that, for a newborn human to be birthed with a brain as well developed as that of a newborn chimp, they would have to gestate for at least—at which point they might run 27 inches from head to toe, and weigh a good 17 or 18 pounds, more than the heftiest bowling ball on the rack.