You mean "reason" in the sense of "why" and he means reason in the sense of "logical conditions". The why is an interesting question, what environmental or other factors provided an advantage in a plant containing this chemical, or was it a non-important side effect of some other change. It is interesting, maybe not easily knowable.

Hope this clears it up. I may be wrong, but I get annoyed when I read comments that are negative without an explanation, so I thought I would attempt to shine some light.