The Receptor Behind the Burn

Why do mammals feel chili heat while birds do not? Capsaicin works by triggering the TRPV1 receptor, the same sensor that fires when mammal tissue is exposed to real heat. Birds carry a version of this receptor that capsaicin barely activates, so the burn that drives mammals away is almost invisible to the plant's preferred seed carriers.

Capsaicin does double duty. Beyond steering seeds toward birds, it also acts as a fungicide that kills seed-attacking fungi during digestion and dispersal.

One molecule, two jobs, refined over millions of years: it picks the right carrier and protects the seed until it lands.