Expert: Walter Hintz - 9/17/2005

Question
Why don't humans (generally) eat leaves? You know, the kind that grow on trees and bushes, not the kind grown by agriculture. Why haven't our bodies adapted to something that seems to have always been plentiful?

Answer
An interesting question Neal and one that I have never had before. Actually we do use all kinds of leaves for nutrition.  The leaves from some trees are used for teas and spices. Groups of people around the world who do have supermarkets eat a lot of plants that grow wild.  There is a big problem with eating all kinds of leaves however.  The carbohydrate in leaves is mainly cellulose and our digestive system does not have digestive enzymes to break down cellulose.  We get no nutrition from such food.
As to your second question:  Adaptation does not come about merely because one kind of energy becomes more available than another.