(un)natural selection: THC?

Jacquelyn's story about the false positive drug test made me consider the chemicals in marijuanna. Out of the hundreds of different compounds in marijuanna (and the thousand plus that are created when combusted), almost a dozen are psychoactive (that we know of). As growers become aware of what seeds produce the most desired product, they repeatedly select the "strongest" strands. This results in a reinforcement process, and a human guided evolution of the plant.

But what does "strongest" actually mean? We are not taking them to the lab and having them tested for THC content, we are gauging by how hard the buds fuck us. While we are obviously increasing the potency of THC with each generation's "weeding out", we can't know for sure the DNA we select each time is not being reinforced for concentrations of chemicals other than THC. While THC is most signicantly psychoactive, extensive research has not been done on the others; much less, all the other chemicals we don't even know about yet, and their possible synergistic effects in combination with THC.

I'm not asserting that we have shaped the evolution of our plants so much so that they have anything but extremely high THC levels, but it is possible, that along the way, we are reinforcing (through consumer preferences) the increase in some other chemical as well.

Also, other confounding features of the plants that shape our (un)natural selection process, are taste, smell, color, shape, density, etc, and number of crystals on the buds (which by the way, keef is supposedly "pure THC crystals", but I have been unsuccessful in finding documentation to verify this). Who knows what chemical changes are held by the same genes which are selected according to these aesthetic preferrences?

(The surprise drug test results just made me consider how often we know very little about what we ingest, even when we grow it ourselves!)