1980 (R. S. Corruccini and J. S. Handler) “Temporomandibular Joint Size Decrease in American Blacks: Evidence from Barbados.” Journal of Dental Research 59: 1528.
We assume that non-genetic, environmental factors have played the major role in TMJ size decrease; the most likely explanation is decreased chewing resistance (and growth stimulation) provided by the soft processed diets of modern urban individuals.