Canine/premolar transposition is rare in both historic and prehistoric Homo sapiens with a known occurrence of less than 0.10%. This report describes a prehistoric population sample from one site (SCrI-3) on Santa Cruz Island, California in which the rate of C/P3 transposition is greater than eight percent, based on nine of 106 adult crania which exhibit the anomaly either uni- or bilaterally. As a means of investigating the etiology of this anomaly, the location of the canine root in adult crania was studied. Root location should indicate tooth bud origin, a factor likely to be under genetic control. In crania with normally erupted canines, the superior portion of the root averages 4.43 mm from alare, while this distance is 8.96 mm for anomalous roots. This difference suggests that during ontogeny the tooth buds for the canine and premolar arose in the wrong (or reversed) places, causing the teeth to erupt anomalously. It is suggested that inbreeding in a small island community resulted in a short-lived appearance of this anomaly at a high frequency. © 1992 Wiley-Liss, Inc.