Eli5: why do chilli plants turn red to attract animals to disperse seeds but also produce the spicy chemical to put them off?
In: 6541
Birds cannot taste spicy flavors, so they can eat hot peppers with no impact. Mammals and many other critters, on the other hand, don’t like the spice and will avoid them. This helps to disperse the seeds further since birds travel further.
This is also why adding spice to your bird feeder can help keep squirrels away!
Evolution doesn’t “do” things for any particular effect or reason. It just does things (mutations). Some of those things fail, and some work. Apparently both of those mutations happened to work and those variations survived. They didn’t “turn red to attract animals”… the red ones attracted some animals, and some of those animals were not bothered by the spicy chemicals so those plants lived to reproduce.
Spicy plants specifically want *birds* to spread their seeds, not mammals. The chemical that makes their fruit taste “hot” to mammals, has no effect on birds.
Their seeds are robust enough to pass through a bird’s digestive system and still germinate on the other side. But mammals’ digestive systems are too harsh for that. So the plant makes the pepper to attract the bird, with a taste that discourages the mammal.
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Actually the red doesn’t really attract mammals, who can’t distinguish red well, except some primates, like humans and a few others.
We evolved to distinguish red to find ripe fruit, whereas for other mammals its not really outstanding.
So the red is used because:
– birds see it
– irrelevant for mammals. Note: peppers are a bit small for big primates anyway
The hot is used to:
– punish inconvenient mammals
– neutral to birds
So its perfectly made to attract birds and avoid mammals.
Working as intended.
Until man came along, and both liked the color and the hot, so the plant got a really good and very unexpected boost to its spread.
##Short answer:
Because birds have eyes too, and they see red better than most mammals do.
##Long answer:
First Factor: The spice is only effective on mammals.
Birds can’t feel it. It’s bad for the plant to have its seeds eaten by mammals (who destroy the seeds as they digest them), but good for the plant to have its seeds eaten by birds (who will poop them out whole and still in working order, and spread them farther away, as they fly.) Birds lack the reaction to the capsaicin (the chemical that makes chili peppers spicy) that mammals have. It’s not a *real* danger to eat capsaicin, but it tricks the nervous system of mammals to send the same pain sensation that actual dangerous things would send.
Second Factor: Birds can see reds better than most mammals can.
i.e. your dog is red/green color blind:
Most mammals only have 2 kinds of cones: a sort of green/blue vision. It’s not that they can’t see red, just that red and green are pretty similar as red things only register as being “very very green, as opposed to a green with some blue in it.” (i.e. red is far enough away from blue that it doesn’t give a residual tickle on the blue receptor like actual green colors would. That’s the only real distinction so it isn’t as stunningly obvious as it is to us.)
Some of the bigger primates, like us humans, have 3-color vision where we see red/green/blue. But that’s an exception among mammals.
And most birds are even better at it than us. They tend to have 4-color vision, a sort of red/green/blue/ultraviolet vision that gives them even more distinction.
So, basically, using a red color to stand out means you’ll stand out to most birds more so than you will to most mammals.
Plants benefit from their seeds being eaten because it helps spread them further and the seed is deposited with it’s own pod manure. However, it is more beneficial for the chili to be eaten by birds because mammals chew their food and thus damage the seeds.
Birds can’t taste capsaicin. So the chili plants with red fruits and lots of capsaicin is more likely to attract birds and repel mammals and thus more likely to produce offspring.
Birds aren’t affected by capsaicin.
Peppers are meant for birds, who will eat the seeds whole, not digest em harshly, and poop em out elsewhere
Peppers are NOT for mammals, who will chew, and fully digest the seeds, destroying the plant’s babies.
Sadly, peppers weren’t prepared for the reality: A lot of humans are masochists to an extent, and get off to the thrill of surviving pain.
Tldr: They’re red so that birds can find em easy. They’re spicey because it hurts mammals who would destroy the seeds
Plants make fruit so that animals eat the fruit and then poop out the seed somewhere far away from the plant. Birds are much better at spreading seeds over large distances than mammals. So what the pepper plant does is make a substance, capsaicin, that makes mammals feel burny and not want to eat the fruit, but doesn’t affect birds at all. So mammals will skip eating the hot peppers, but birds will eat them just fine, and the plant gets maximum seed spread at the lowest cost.
Humans were an unexpected development, but it worked out extremely well for the species.
Because it has worked and theyve survived up to this point
Its not like they can just choose what color to be
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