Humans are likely less adapted to plant defense chemicals than their primate ancestors.

“So, one way is a bitter taste. The second way is vomiting. A third way, which is interesting from a human environmental health standpoint, is we have evolved enzymes in our liver that rapidly remove these potentially toxic chemicals when we eat them. They're called cytochrome P450s. Okay. But the fourth way is that the individual cells in our body have evolved to respond to some of these chemicals by, for example, enhancing their antioxidant defenses or enhancing their ability to even extrude the chemicals.”