This leads to deterioration of agriculture and lessens the production.
This deterioration increases with the number of successive copyings.
In the i4th century there is a significant deterioration in the monastic chroniclers, and their place is taken by the works of secular clergy like Adam Murimuth, Geoffrey the Baker, Robert of Avesbury, Henry Knighton and the anonymous author of the Eulogium historictrum.
This was, however, more probably due to the deterioration of the country through desiccation, which has forced the settled population farther westward, where Sana became the centre of the later Himyaritic kingdom.
If, in these circumstances, the food supply be also insufficient, the combination of influences is sure, in course of time, to bring about a physical deterioration of the race.