Questions about poison ivy and evolution?

I just got poison ivy and it got me thinking: what were the evolutionary pressures to make plants poisonous to the touch? As far as I can tell humans are effected more by poison ivy than other animals (I'm basing this pretty much on dogs and cats). Also the rash doesn't appear right away so the only animal smart enough to make the connection between poison ivy and its rash is probably humans. I don't think keeping humans from touching it would have been strong enough pressure alone to cause the evolution of its poison. I think that the plant must smell bad or taste bad to keep other animals from eating it. So that leads to a few other questions. What happens if you eat poison ivy? And does the plant have a specific smell to it? Also I've heard that if you burn poison ivy and inhale the smoke it's really bad. Is that true? What happens to you?





I'm bored and loaded with caffeine, hence the rambling.

Questions about poison ivy and evolution?
Why would animals eating poison ivy not make the connection? It is an evolved plant defense against being eaten.
Reply:Urushiol, the active compound in poison ivy can be carried in smoke.





The compound is not intrinsically toxic, but interacts with many tissue types to produce an allergic response.





Many people do not have responses. It appears to be an incidental reaction to the compound, and if it impacted survival, sensitive tissue types would fade from the population.
Reply:Yeah, that's a good question, and I've wondered that myself. I too wouldn't think that the negative connection with poison Ivy is immediate enough to help with the survival of the plant. Think of this too - maybe the Ivy we're familiar with now is not the final product, and is still developing in to something that will at some point provide a more rapid reaction to a threat. Anyway, I do know that all plants produce a byproduct of metabolism, which is an acid. Mammals (including humans) do too, which is discarded in urine. Most plants leach the acid out through roots, leaves, or needles. But the Poison Ivy and Poison Oak, and others secrete the acid onto the leaves where it dries into crystals. When the crystals get in our skin they create an allergic histamine reaction. The crystals can remain active for a year on seasonal clothing and other items.
Reply:evolution isnt real dumbssa

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