These are very odd questions to be asking–especially for someone preparing to teach evolutionary biology. Before asking those questions, you need to ask this question: Are there mechanisms of evolution that guide evolution to produce traits other than those that improve reproductive success? These are the known mechanisms of evolution:
- mutation (a random process, does not occur to meet some desired end goal)
- gene flow (the movement of alleles/traits geographically)
- genetic drift (this increases frequency of certain traits randomly, not to meet some desired end goal)
- non-random mating (this just puts alleles together in certain combinations and doesn’t really increase or decrease frequency of traits over time)
- selection (this increases the frequency of traits that confer a reproductive advantage of the organisms as they function within their particular environment at the moment, not to meet some desired end goal)
There are no other evolutionary mechanisms that we know of, and none of these will create organisms with traits that serve some grander purpose. None are goal oriented. Organisms alive today have the traits that they do for no other reason than this: that those were the particular traits, of the many alternative traits produced by mutation, that happened to improve [or did not considerably hinder] the reproductive success of their ancestors within the context of their ancestor’s environment.
Plant toxins typically evolve probably to reduce herbivory. Those that are pyschedelic may just happen to be so just by coincidence. After all, snow can be used to create snowmen, but I doubt that is its purpose. It’s really difficult to know exactly why any particular trait happened to evolve and not another alternative trait. There are often multiple traits that are equally suited to solving a particular problem (for keeping warm for example: hair vs. feathers vs. behaviors that allow organisms to move to locations that are the best temperature all work equally well as we see many birds, mammals, and “cold-blooded” animals doing quite well). It’s just which particular series of mutations occurred along the ancestral lineage of an organism.
Related to this are what we call “just-so” stories. Rather than starting by asking “what is the purpose of this trait?” and then making up a story that sounds good, one always needs to first ask “does this trait have a purpose”?
There are several good articles about “just-so” stories. Here’s one and here’s another.