[agilob]

I don't think they are unlearning how to eat other things. It's humans who will have to find a new way to build cars, planes, boxes, bottles and electronics. Think how expensive it will be once car tire or fiber-optic cable eating bacteria hits a major city. Your access to fresh food will be limited and you don't even have a single apple tree.

[FarmerPotato]

It turns out there are a lot of microorganisms (and bigger) that attack your apple trees. Nothing is easy.