As the majority of chewers were children, this would seem to suggest that tar was a treat or a treatment - unless children were given the job of preparing tar for the tasks of the community. This is why harvest-time is so chancy for the farmer. If the weather is very wet, and he can't get his machinery on the fields when the grain is ripe, it does shed, and even germinates and grows up through the existing crops if the delay is prolonged. A genetic change has therefore taken place.
Wild cereals shatter more easily than cultivated cereals when ripe.
In modern farming, some cultivated grains may be lost during harvesting, but most remain attached to the ear. Gordon Hillman of the Institute of Archaeology in London has shown that sickle reaping of ripe wild plants would cause seed loss, except among the rare non-shattering mutants. If seeds collected this way were replanted and the process repeated, this would gradually select for nonshattering heads. Perhaps this is how the genetic change occurred. Two issues struck me.