Can you eat as many chili peppers as a Chinese tree shrew? Probably not. A recent study found that these tree shrews are the only mammal aside from humans known to deliberately seek out spicy foods.

Researchers in China found a mutation in the species’ ion channel receptor, TRPV1, that makes it less sensitive to capsaicin, the “hot” chemical in chili peppers.

This is the channel that acts as a pain receptor on the tongues and throats of mammals, alerting the brain when it comes in contact with harmful heat. (Read the history of spicy peppers in human cuisine.)

But thanks to the genetic mutation, tree shrews don’t feel as much pain from spicy food.

Field Observations

Yalan Han, of the University of Chinese Academy of Sciences, and colleagues knew that the Chinese tree shrew is closely related to primates and likes to eat spicy plants in its native habitat in the tropical rainforests of south east China.

For the study, the scientists captured five wild tree shrews and six wild mice—controls for the experiment—and collected samples of Piper boehmeriaefolium, a capsaicinoid-rich Chinese plant, from a local botanic garden.

The scientists then synthesized the capsaicins from the plant and injected both groups of mammals with the substance. The team measured the animals’ pain response by observing how much they licked the injection site. Not surprisingly, the mice licked the injection site more than the tree shrews. (Read how spice tickles your lips.)

All the animal subjects were then humanely euthanized and decapitated, and their brains were observed via microscope, according to the study, published July 12 in the journal PLOS Biology.

Between the tree shrews and mice, scientists found only a single amino acid allowed the tree shrews to eat spicy food without feeling intense pain.

Born With It

The researchers believe that the mutation that allows these shrews to munch on chili peppers is the same one responsible for their ability to eat P. boehmeriaefolium without feeling pain.

Many plants have evolved to contain pungent chemicals that dissuade animals from eating them, but in this case, the tree shrew evolved the upper hand.

“We propose that this mutation is an evolutionary adaptation that enabled the tree shrew to acquire tolerance for capsaicinoids, thus widening the range of its diet for better survival,” Han said in the study.