There's all kinds of varieties and spontaneous genetic variations in nature. That's why we have more than one sort of lettuce, sweet peppers, squash and so on. Its quite possible the current "potato" as we know it was selectively bred to have a higher amount of starches and sugars than it did originally.

The modern day turkey is selectively bred such that it has a breast that is so fat it can't reproduce on its own. A male turkey's breast is so big it can't mount the female. They used to drive turkeys to market, herding them along. They say nowadays you couldn't do that with a turkey, they're bred to become so fat they'd die of heart attacks before they ever got to the market.

Not all frankensteins come from a test tube, folks.