The human body is an extremely efficient consumer of food stuffs, but is a poor manufacturer of the basic ingredients necessary to sustain life. Most of the vitamins, trace minerals, and particularly the amino acids necessary to build body protein must come already prepackaged in the food stuffs consumed. None are manufactured in the process of digestion, but are indeed, broken out of the food stuffs in the digestion cycle. So long as societies depended on hunting and the consumption. of red meat, most of the necessary amino acids were available in sufficient quantity. The move to small grain culture was another matter.
Small grains are very low in lysine and wheat contains virtually no tryptophane.
The problem was that domesticated animals also ate the small grains. Consequently, early society tended to divide its labor at nearly the same time between cultivation and herdsmen. A biotic relationship developed between the two groups. The meeting grounds for the exchange of food stuffs were called cities. It is likely not simply a coincidence that Neolithic man is credited with the beginnings of settled agriculture and also the building of the first towns.