Science Figures Out Why the Tree Shrew Eats Red-hot Peppers

Send in e-mailSend in e-mail
Send in e-mailSend in e-mail
Go to comments
Tree shrew
Tree shrewCredit: MA Xiaofeng
Ruth Schuster
Ruth Schuster
Ruth Schuster
Ruth Schuster

Why anybody eats food that makes them cry is still heatedly argued among the scientific set. But now we know why the tree shrew eats hot peppers, thanks to the Chinese Academy of Sciences: it's a mutant.

How can the tree shrew eat this without cringing?Credit: Limor Laniado Tirosh

Most mammals are sensibly repelled by painful sensations. Give a monkey a chili pepper and he won't take another from you, or anything else probably. But the tree shrew happily gorges on the brightly colored fruit even though they don't live anywhere near where peppers grow.

"Researchers accidentally observed tree shrews directly and actively consuming chili peppers, despite the deep geographic isolation between the animal and the food," write Prof. Lai Ren from the Chinese Academy of Sciences along with researchers from Zhejiang University in PLOS Biology.

Tree shrews, also known as banxrings by them as can pronounce that word, are not shrews. They just look somewhat like shrews, hence the misleading nomenclature. In fact their closest relatives are primates, meaning they're a lot closer to you than your dog.

Tree shrews live in Southeast Asian forests and are best known for having giant brains, relative to their small bodies, that is. There are a lot of species of so-called tree shrew and not all live in trees. Now it has been observed that the ones known to science as Tupaia belangeri chinensis like to eat hot peppers, which don't grow in the trees where these nice animals hang.

Genetic sequencing of the Tupaia tree shrew was enlightening. The Chinese scientists concluded that the heat-happy proto-primate has a mutated version of the gene TRPV1, which stands for "transient receptor potential vanilloid type-1."

It's just one mutation at one point in one gene, but it may have done the trick, lowering the animal's sensitivity to capsaicinoids, the active chemical in chili peppers that you feel coming in, and going out.  Peppers cause no physical damage, by the way. It just feels like they're burning you to death.

Garnishing an avocado toast with hot pepper. Why??Credit: David Bachar

Morning glory

Given that chilis don’t grow where the tree shrews do, how would the mutation become prevalent through generations of tree shrew?

The scientists suspect it arose from proximity to Piper boehmeriaefolium, a spicy plant that geographically overlaps with the tree shrew and produces Cap2, a capsaicin analog, they explain.

They hypothesize that the tree shrew adapted to eat the spicy P. boehmeriaefolium by positive selection.

Where did red peppers originate, anyway? Scientists are still tracking the development of the Capsicum genus, which belong to a botanical family called the nightshades, or Solenales. This family encompasses a vast range of plants from the tomato to tobacco to petunia to the spicy red hot pepper that makes us weep.

Originally thought to have begun evolving in South America, this year a 57-million-year-old fossil looking very much like morning glory, a relative of the sweet potato was found in Meghalaya, northeast India. Now the thinking is that morning glories originated on the part of the crumbling Gondwana supercontinent that would become Asia.

And maybe, as mammals proliferated wildly following the demise of most of the dinosaurs, they ate freely of the fruit around them, and some mutated in order to eat that pretty bright-colored fruit, which is chock full of good things like vitamins.

Bats living in the Negev were discovered to feast on scorpions even though they would absolutely get bitten and it would totally hurt. But then what choice do they have.

We and tree shrews do have choices. So why do have people been eating hot pepper for at least 9,000 years? Jason Goldman writing in Scientific American delivers a remarkable list of synonyms for the peppers (from "Pain is good" to "mother pucker") and points out that the sane do not stab themselves in the eyeballs. So we don't know. The best guess is "benign masochism".