Chili pepper science

University of Washington ecologist Joshua Tewskbury spends much of his time on a quest for wild chili peppers. Fueled by coca leaves, he is seeking answers to questions about the evolution of the plants, specifically why wild chilis are hot. In central Bolivia, Tewksbury is exploring the natural function of capsaicin, the heat-generating chemical found in the plant. Smithsonian's Brendan Borrell recently went into the forest with him. From Smithsonian (Wikimedia Commons photo):
Bolivia is believed to be the chili's motherland, home to dozens of wild species that may be the ancestors of all the world's chili varieties–from the mild bell pepper to the medium jalapeño to the rough-skinned naga jolokia, the hottest pepper ever tested. The heat-generating compound in chilies, capsaicin, has long been known to affect taste buds, nerve cells and nasal membranes (it puts the sting in pepper spray). But its function in wild chili plants has been mysterious.

Which is why Tewksbury and his colleagues have made multiple trips to Bolivia over the past four years. They're most interested in mild chilies, especially those growing near hot ones of the same species–the idea being that a wild chili lacking capsaicin might serve as a kind of exception that proves the rule, betraying the secret purpose of this curiously beloved spice...

"Capsaicin demonstrates the incredible elegance of evolution," says Tewksbury. The specialized chemical deters microbes–humans harness this ability when they use chilies to preserve food–but capsaicin doesn't deter birds from eating chili fruits and spreading seeds. "Once in a while, the complex, often conflicting demands that natural selection places on complex traits results in a truly elegant solution. This is one of those times."
"What's So Hot About Chili Peppers?"


  1. The hot substance is capsaicin that binds to nerves (on the “C fiber receptor”). Birds lack this receptor and they also lack teeth, minimizing the risk of grinding the seeds.
    So: put chili in a fruit: the seeds will pass unharmed through the animal and will travel farther than in a rodent.

  2. #1: That’s certainly the evolutionary advantage I’ve always assumed.

    Humans are weird creatures who _like_ sublethal intoxication in some cases, and/or have learned to mix foods to bring the toxic/irritative component down to a tolreable level.

  3. It’s “Brendan Borrell” not “Brenan Borrell”. =) Sorry to nitpick, old classmate, can’t be helped.

  4. Doesn’t the fact that the very attribute that repels one kind of predator attracts another kind (humans), decreases the effectiveness of the chilis being hot?

    I am just wondering about ways in which humans start affecting evolution.

  5. I was going to chime in with #1 as well. Nature’s way of saying – no, this stuff is for the birds only.

  6. #4: Becoming tasty to humans is probably an asset, not a liability. At least, as long as you’re also easy to cultivate.

    Humans don’t like eating pepper seeds much (bonus for the plant), and we’ve gone out of our way to transport them across the planet and help them grow in all sorts of environments they’d never have reached from Bolivia, even with migratory birds helping.

  7. @4 – See M Night Shyamalan’s The Happening.
    @8 – Yeah that’s the first thing I caught too. Not that I’m judging him, he’s more than welcome to whatever substances he wants to ingest, I just find it funny they actually mentioned it specifically.

  8. @#8 XraySpecs: Yeah, I lol’d at how casually that was mentioned. No biggie… dude’s high as a kite, but chilies MUST be studied all the while. Sounds good in my book. Chilies are such an important cooking and pickling ingredient for me.

  9. What the fuck does anyone mean by “the exception that proves the rule”? By its very nature, an exception should completely derail a rule and send it hurdling into a flaming demise. Especially for describing natural phenomena. Sure, non-hot chilies invite further inquiry so that the current model of chili evolution can be appropriately modified, but they definitely don’t prove the current rule.

  10. Um… Chewing coca leaves as a mild stimulant would probably have nowhere near the same degree of psychoactiveness as refined cocaine…

  11. @#12 – It makes more sense if you use an older meaning of the word “prove”. It comes from the Latin “Probare”, meaning “to test”, as in probe, probity, probation, etc. So an exception will “prove” the rule, and find it wanting. Just don’t mention the pudding…

  12. now i am wondering if capsaicin acts the same way on birds’ digestion as in humans: specifically to speed digestion. it could be nature’s way of getting the seeds out the other end much faster.

  13. What the fuck does anyone mean by “the exception that proves the rule”?

    ♥ The premise: All duck species quack.
    ♥ The exception: I’ve found a duck species that doesn’t quack.
    ♥ The proven rule: Not all duck species quack.

  14. Manooshi: Cocoa leaves are more like a few cups of strong coffee. Cocaine is refined from the leaves. Lots of them. Sticking one in your mouth for half an hour yields a totally different effect.

    Assumptions. Ass. You. Leave me out of it.

Comments are closed.