It also doesn't address the fact that we've been genetically modifying (read: breeding) plants to be eaten for around 10,000 years. Most of the plants we eat are nothing like their wild antecedents. Compare maize to teosinte, for instance. Or cultivated potatoes to the wild tubers they were bred from -- the wild ones will kill you, full stop.

(As an aside, I highly recommend Bill Bryson's "At Home," which discusses these topics and many more related to how we came to live the lives we do -- it's a great companion to A Short History of Nearly Everything.)