critical not restricted (add a comma)

David W. Anthony, in “The Horse, The Wheel, and Language”, on the peak of the Old Europe (lower Danube valley, end of the 5th millennium BCE):

The crafts of metallurgy, ceramics, and even flint working became so refined that they must have required master craft specialists who were patronized and supported by chiefs. In spite of this, power was not obviously centralized in any one village. Perhaps, as John Chapman observed, it was a time when the restricted resources (gold, copper, Spondylus shell) were not critical, and the critical resources (land, timber, labor, marriage partners) were not seriously restricted.