In nature, there are various herbs and plants, which manufacture chemicals with theraupatic properties for humans and animals.
Did those plants evolve this ability to manufacture chemicals by themselves? Or were they artificially bred (or even genetically engineered) to do so by a long-lost civilization, which may have existed thousands of years ago?
This question suggests that a research be made about the metabolic pathways, which are used to create those chemicals. Two questions are of inerest:
- Do the metabolic pathways need the involvement of special genes? If yes, it is a hint about artificial genetic engineering.
- Do the chemicals have other uses in the plant’s lifecycle? If yes, then the metabolic pathways could have been created by evolution.
(No, creationism is not a valid answer.)
I already suggested to check if a chemical-producing herb needs the chemical also for its own uses.
A chemical, which shows up at different levels in different organisms, changes only partially the question. For it, the interesting question would be why would a particular herb bother to maintain it at high concentration levels.
The vitamin C example is not really representative. Vitamin C is a dietary supplement, which needs to be consumed all the time. So providing it does help pollinate the providing plant. Medications are needed only when one (human or animal) is sick. So they cannot be relied upon to attract pollination facilitators.
However, I suspect this is a case of “all the above answers are correct”. There are so many varieties of living organisms, and herbs in particular, that almost each possible variation would probably be seen in at least one variety of living organism.
Since I am not into creationism and Atlantians, I would bet that the answer is simpler. either the plant needs that chemical, or that plant has a benefit of other animals eating it because they need the chemical and thus help polinate it, or that the chemical is nothing special and shows up in different organisms at different levels. for instance, humans and other mammels lost the ability to produce enough vitamin C some few million years ago, hence are dependency on certain fruits in our diet. I would bet that citrus fruits got a lot of good seedings once they started producing higher vitamin C concentrations, so as usual, everybody wins.