No, Pot like every other plant known to man evolves and changes, especially when humans purposely breed it for certain things. In the case of Pot, it's been bread for potency, at any given time the less potent stuff is of course worth less money, so there is a drive to make it more and more potent. There are many strains of cannabis, just like most other types of consumable plant. Hence different colored and sized apples, etc.
In the case of foods, new strains have been genetically created. I honestly don't know much about the process, but you can definitely change things... the corn we grow now is nothing at all like what the natives originally grew here.
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