Explorers throughout history employed similar techniques when foraging edibles in new environments."Considering how few plants are used by the great apes..food, in comparison with the very great number eaten by primitive peoples in recent times, the experimental consumption of an ever-increasing variety of food-stuffs may be regarded as one of the important conquests of human evolution.Your librarian will be happy to help you find a copy.] "Homo erecutus may have used fire to a very limited extent some 300,000 years ago, but the evidence is sparse and questionable.Fire's general use, according to both paleontological and archaeolgical records, began only about 40,000 to 50,000 years ago..."For hundreds of thousands of years the evolving human race had eaten its food raw, but at some time between the first deliberate use of fire--in Africa in 1,400,000BC or Asia in 500,000BC (depending on which theory happens to be the flavour of the month)-and the appearance of the Neanderthals on the prehistoric scene, cooking was discovered.
Based on this evidence, they presume foods were selected or rejected based on observation (they were avoided by the other animals in the area) in conjuction with basic trial and error (if it made the taster sick, it was unlikely others partook).
The use of fire, extended to food preparation, resulted in a great increas of plant food supply.
All of the major domesticated plant foods, such as wheat, barley, rice, millet, rye, and potatoes, require cooking before they are suitable for human consumption.
It is, of course, impossible to gauge with any certainty as what stage in the million of years of human evolution the quest for a much wider food horizon began.
Probably the utilization of new vegetable foodstuffs was a gradual development; it would obviously vary according to the plants available in a particular area.