Toxic substances in plants and the food habits of early man

Science. 1972 May 5;176(4034):512-4.
Toxic substances in plants and the food habits of early man.
Leopold AC, Ardrey R.
The widespread occurrence of toxic substances in plants must have greatly restricted their usefulness as food for primitive man. The development of cooking of plant products is suggested to have been a major evolutionary advance, making a major increase in the vegetable materials palatable to man; this technical advantage apparently occurred only in the most recent 2 percent of the anthropological record.