The Pain of Altruism
Pain functions to alert an animal to potential damage and to reduce activity after trauma. Pain may also motivate social activity. In certain circumstances, the presence of others can affect the intensity of pain.
Across all human cultures, women receive help in birthing. In contrast, solitary birth is the norm for other primates.
The source of human labor pain comes from the contraction of the uterus and dilation of the cervix. This pain signals a risky and potentially lethal event hours later: birth. The delay between the onset of pain and delivery affords opportunity to enlist assistance.
Childbirth for women is uniquely painful. This owes to a size mismatch between a baby’s outsized head and its mother’s pelvis.
Women are not the only primates at risk when birthing. Marmosets have similar head-to-pelvis disproportionality and birth-related mortality. Yet marmosets and other mammals give birth rather painlessly. Ungulates birth large, long-limbed offspring with substantial chance of complications but little evident distress.
As other animals must often carry on by themselves, putting them in pain to deliver offspring would be insensible, whereas with women pain provokes altruism and social bonding at a critical period of life for both mother and child.