The Somerton man was missing his top lateral incisors. I've done some googling on this and while the lateral incisors are the most common teeth to be genetically missing, the condition itself is not what would be called common. About 2% of the world population has genetically missing top lateral incisors. (In many of these cases, the missing teeth occur in people with Down's Syndrome and other syndromes which would have been obvious in the person's appearance. Somerton man didn't look like he had any obvious genetic syndromes.) I understand that "Jestyn's" son Robin also was missing these teeth. If only about 2% of the population has this anomaly, and if many of that 2% have Down's Syndrome and various other genetic syndromes, then if the Somerton man (who didn't appear to have any obvious syndromes) and Robin both had this same anomaly (Robin not being afflicted with any known genetic syndromes), then it seems quite likely that the theory is true that Robin was the Somerton man's son.