Early Agricultural Systems The stimuli for man's development of agricultuire in prehistoric times probably were encountered in open areas of grasslandl, in the steppes, the prairies and the savannas. How agriculture actually came about may never be determined, but surely there must have been a logical sequence of accidental discoveries. We may imagine incursions into the grasslands to hunt the plentiful game; the normal tendency persisting today in man to keep an occasional young wild animal when food was plentiful; and the early discovery of which could be domesticated anid even thrive attached to man. Perlbaps such aniimals were found to be useful as decoys to aid his nomadic hunting andl it is nlot difficult to imagine his earlydiscovery of the possibilities of milking and riding some of his domesticated beasts. The supplementing of his meat diet with fruits and wild grains would seem to have led normally to the development of specific routing of his wanderings during harvest seasons, subsequent settling in the vicinity of rich areas of game and wild plant crops and eventually on to actual tillage in combination with the herding of domesticated stock. Over the milleniia from some such tentative agricultural beginnings, man has refined his agricultural techniques, crops and animals, prospered and multiplied himselff manyfold and extended his domaini into the far corners of the globe with all their varied climates. The steppe-prairie type of agriculture was expanded early and successfully into the semi-arid and arid reg-ions with the development of irrigation. This was again a logical development since there they found high fertility of the soils and the low successional pressure of weed growth could readily be controlled with hand labor and primitive techniques. Salinization and siltation were the main problems, but high productivity was attained even in early times (1). At Girsu in Central Iraq, records show that wheat yields in 2400 B.C. averaged 2537 liters or 72 bushels of grain per hectare as compared with the USA average in 1958 of 67y2r bu. per hectare. The same steppe-prairie type of agriculture was brought long ago to the tropical regions and in the Americas revolved primarily around the production of maize. Again the centers developed in and around the grasslands: the Mayan Civilization, the savannas of Mexico and Guatemnala; the Chibchas, the savanna at Bogota, Colombia; and the Incas centered on the montane prairies and steppes of highland Peru. In the latter place, from the ecological point of view, we should look first of all for the natural ancestor or ancestors of maize. Conditions in such montane and lower montane belts of the tropics are quite similar in general climatic characteristics to the corresponding areas of the temperate regions. It is perhaps significant that of these civilizations in the Americas in prehistoric times, the one that succumbed first, even before the arrival of the Spaniards, was