According to Jared Diamond's Guns, Germs and Steel (pp 125-126), the domestication of local grains (e.g. wheat, barley) and pulses (e.g. peas, lentils) lauched food production (farming) societies in many areas. Grain crops have the advantage of being fast-growning, high in carbohydrates and high yield per area cultivated. Their low protein is made up by pulses which are often >25% protein (e.g. soybeans has ~38%). This makes these two types a good combination. The author proceeded to list many parallel combination of grains (or cereals) and pulses in many early farming communities:
My question is, given their lack of knowledge about biochemistry, how did these societies learn about the advantage of pulses' protein contents and the importance of balanced carbohydrate-protein diet? Or did they unconsciously do it, for example were there some evolutionary/selection process that caused people who consumed balanced diet to survive and produce more offstring? If so, what made this combination invariably "win" in many areas?