New Statesman has a fascinating article on the ‘cultural history of pain’ that tracks how our ideas about pain and suffering have radically changed through the years.
One of the most interesting, and worrying, themes is how there have been lots of cultural beliefs about whether certain groups are more or less sensitive to pain.
Needless to say, these beliefs tended to justify existing prejudices rather than stem from any sound evidence.
Some speculated whether the availability of anaesthetics and analgesics had an effect on people’s ability (as well as willingness) to cope with acute affliction. Writing in the 1930s, the distinguished pain surgeon René Leriche argued fervently that Europeans had become more sensitive to pain. Unlike earlier in the century, he claimed, modern patients “would not have allowed us to cut even a centimetre . . . without administering an anaesthetic”. This was not due to any decline of moral fibre, Leriche added: rather, it was a sign of a “nervous system differently developed, and more sensitive”.
Other physicians and scientists of the 19th and early 20th centuries wanted to complicate the picture by making a distinction between pain perception and pain reaction. But this distinction was used to denigrate “outsider” groups even further. Their alleged insensitivity to pain was proof of their humble status – yet when they did exhibit pain reactions, their sensitivity was called “exaggerated” or “hysterical” and therefore seen as more evidence of their inferiority.
Link to New Statesman article (via @SarahRoseCrook)
Mind Hacks 
” But this distinction was used to denigrate “outsider” groups even further. “…yes, the category determines the destiny..and what group is defined and categorised more rigidly than most when it comes to treatment meted out than those in the “non-human animal” category? Bernard Rollin (“The Unheeded Cry”) describes how various outsider groups went through the (agonising) process of being admitted to a category where their pain mattered: the inclusion of neonates as candidates for major surgery with only muscle paralysants, not anaesthesia, until the ’60’s should not surprise us, given that we know perfectly well that pain is felt by all animals, vertebrate and invertebrate, but we still feel justified in doling it out for trivial reasons on the grounds of difference of category only.