What is the evolutionary advantage for a plant to have a spicy fruit? I thought the purpose of fruit was to use animals for better seed dispersion, but having a fruit that causes a burning sensation in the mouth would seem to be a disadvantage. The only thing I can think of is that peppers have either been cultivated by humans to be spicy, or some animals are not affected by whatever causes the burning sensation.
Capsaicin (the chemical in peppers that causes the “burn”) only affects mammals. Birds are unaffected. It’s reasonable to assume that, for some reason, it’s evolutionarily advantageous for peppers to have birds disperse their seeds and for mammals to leave them alone. (Perhaps mammals have too small a range, overgraze the plants, etc.)
Birds aren’t affected by the capsaicins in peppers, and are the primary disperser of the seeds.
Already answered, but SDSTAFF Colibri has covered this, as well.
I came at this thread from another direction. We humans and some others mammals have developed the ability to produce endorphins in response to capsaisin. That’s “darn good intelligence,” in my view. The capsaisin is wasted on the birds, not on us. The birds will never say, “Ahhyee!” in response to a splendid pepper, and they are much the poorer for it. They’ll never lose their car keys, either, but I think we came out ahead.