Should we be surprised that the descendents of Vikings have a high pain tolerance? From Stoic Redheads:
Redheads have long been portrayed in literature and art as strong-willed and fiery. Now there may be a scientific explanation for these traits. The key, according to researchers at McGill University in Montreal, is a gene that is linked both to red hair coloring and to higher levels of pain tolerance. It has been known since the mid-1990′s that mutations of the MC1R gene are responsible for hair color — and fair skin and freckles — in about 70 percent of redheads.
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When animals and humans experience pain, their brains release natural opiates similar to morphine. In most cases, however, the MC1R gene produces a protein that interferes with the efficacy of those substances as well as of artificial painkillers. What Mogil found is that the variant of MC1R that causes red hair also appears to allow these opiates to work unimpeded. As a result, redheads can withstand up to 25 percent more pain than their blond and brunet peers do before saying ‘stop.’