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The Pain of Altruism

All vertebrates feel pain. 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, females 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.

Human childbirth appears to be uniquely painful. Physiologists have accounted for this owing to a size mismatch between an infant's head the mother's pelvis; not because of social proclivities.

But humans 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 produce large, long-limbed offspring with substantial chance of complications, but little evident distress.

As other animals must often carry on by themselves, the evolutionary role of pain for them is more circumscribed than in humans, where altruism plays a regular motivational role.

Sources:

Barbara L. Finlay & Supriya Syal, "The pain of altruism," Trends in Cognitive Science 18(12): 615–617 (December 2014).

Charlotte Krahé et al, "The social modulation of pain: others as predictive signals of salience – a systematic review," Frontiers in Human Neuroscience (23 July 2013).

Barbara Finlay, "It hurts to be human: why pain is fundamentally different for us," New Scientist (11 May 2015).

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